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PERLFUNC(1)			 Perl Programmers Reference Guide		      PERLFUNC(1)

NAME
       perlfunc - Perl builtin functions

DESCRIPTION
       The functions in this section can serve as terms in an expression.  They fall into two
       major categories: list operators and named unary operators.  These differ in their
       precedence relationship with a following comma.	(See the precedence table in perlop.)
       List operators take more than one argument, while unary operators can never take more than
       one argument.  Thus, a comma terminates the argument of a unary operator, but merely
       separates the arguments of a list operator.  A unary operator generally provides scalar
       context to its argument, while a list operator may provide either scalar or list contexts
       for its arguments.  If it does both, scalar arguments come first and list argument follow,
       and there can only ever be one such list argument.  For instance, splice() has three
       scalar arguments followed by a list, whereas gethostbyname() has four scalar arguments.

       In the syntax descriptions that follow, list operators that expect a list (and provide
       list context for elements of the list) are shown with LIST as an argument.  Such a list
       may consist of any combination of scalar arguments or list values; the list values will be
       included in the list as if each individual element were interpolated at that point in the
       list, forming a longer single-dimensional list value.  Commas should separate literal
       elements of the LIST.

       Any function in the list below may be used either with or without parentheses around its
       arguments.  (The syntax descriptions omit the parentheses.)  If you use parentheses, the
       simple but occasionally surprising rule is this: It looks like a function, therefore it is
       a function, and precedence doesn't matter.  Otherwise it's a list operator or unary
       operator, and precedence does matter.  Whitespace between the function and left
       parenthesis doesn't count, so sometimes you need to be careful:

	   print 1+2+4;      # Prints 7.
	   print(1+2) + 4;   # Prints 3.
	   print (1+2)+4;    # Also prints 3!
	   print +(1+2)+4;   # Prints 7.
	   print ((1+2)+4);  # Prints 7.

       If you run Perl with the -w switch it can warn you about this.  For example, the third
       line above produces:

	   print (...) interpreted as function at - line 1.
	   Useless use of integer addition in void context at - line 1.

       A few functions take no arguments at all, and therefore work as neither unary nor list
       operators.  These include such functions as "time" and "endpwent".  For example,
       "time+86_400" always means "time() + 86_400".

       For functions that can be used in either a scalar or list context, nonabortive failure is
       generally indicated in scalar context by returning the undefined value, and in list
       context by returning the empty list.

       Remember the following important rule: There is no rule that relates the behavior of an
       expression in list context to its behavior in scalar context, or vice versa.  It might do
       two totally different things.  Each operator and function decides which sort of value
       would be most appropriate to return in scalar context.  Some operators return the length
       of the list that would have been returned in list context.  Some operators return the
       first value in the list.  Some operators return the last value in the list.  Some
       operators return a count of successful operations.  In general, they do what you want,
       unless you want consistency.

       A named array in scalar context is quite different from what would at first glance appear
       to be a list in scalar context.	You can't get a list like "(1,2,3)" into being in scalar
       context, because the compiler knows the context at compile time.  It would generate the
       scalar comma operator there, not the list construction version of the comma.  That means
       it was never a list to start with.

       In general, functions in Perl that serve as wrappers for system calls ("syscalls") of the
       same name (like chown(2), fork(2), closedir(2), etc.) return true when they succeed and
       "undef" otherwise, as is usually mentioned in the descriptions below.  This is different
       from the C interfaces, which return "-1" on failure.  Exceptions to this rule include
       "wait", "waitpid", and "syscall".  System calls also set the special $!	variable on
       failure.  Other functions do not, except accidentally.

       Extension modules can also hook into the Perl parser to define new kinds of keyword-headed
       expression.  These may look like functions, but may also look completely different.  The
       syntax following the keyword is defined entirely by the extension.  If you are an
       implementor, see "PL_keyword_plugin" in perlapi for the mechanism.  If you are using such
       a module, see the module's documentation for details of the syntax that it defines.

   Perl Functions by Category
       Here are Perl's functions (including things that look like functions, like some keywords
       and named operators) arranged by category.  Some functions appear in more than one place.

       Functions for SCALARs or strings
	   "chomp", "chop", "chr", "crypt", "fc", "hex", "index", "lc", "lcfirst", "length",
	   "oct", "ord", "pack", "q//", "qq//", "reverse", "rindex", "sprintf", "substr",
	   "tr///", "uc", "ucfirst", "y///"

	   "fc" is available only if the "fc" feature is enabled or if it is prefixed with
	   "CORE::".  The "fc" feature is enabled automatically with a "use v5.16" (or higher)
	   declaration in the current scope.

       Regular expressions and pattern matching
	   "m//", "pos", "qr//", "quotemeta", "s///", "split", "study"

       Numeric functions
	   "abs", "atan2", "cos", "exp", "hex", "int", "log", "oct", "rand", "sin", "sqrt",
	   "srand"

       Functions for real @ARRAYs
	   "each", "keys", "pop", "push", "shift", "splice", "unshift", "values"

       Functions for list data
	   "grep", "join", "map", "qw//", "reverse", "sort", "unpack"

       Functions for real %HASHes
	   "delete", "each", "exists", "keys", "values"

       Input and output functions
	   "binmode", "close", "closedir", "dbmclose", "dbmopen", "die", "eof", "fileno",
	   "flock", "format", "getc", "print", "printf", "read", "readdir", "readline"
	   "rewinddir", "say", "seek", "seekdir", "select", "syscall", "sysread", "sysseek",
	   "syswrite", "tell", "telldir", "truncate", "warn", "write"

	   "say" is available only if the "say" feature is enabled or if it is prefixed with
	   "CORE::".  The "say" feature is enabled automatically with a "use v5.10" (or higher)
	   declaration in the current scope.

       Functions for fixed-length data or records
	   "pack", "read", "syscall", "sysread", "sysseek", "syswrite", "unpack", "vec"

       Functions for filehandles, files, or directories
	   "-X", "chdir", "chmod", "chown", "chroot", "fcntl", "glob", "ioctl", "link", "lstat",
	   "mkdir", "open", "opendir", "readlink", "rename", "rmdir", "stat", "symlink",
	   "sysopen", "umask", "unlink", "utime"

       Keywords related to the control flow of your Perl program
	   "break", "caller", "continue", "die", "do", "dump", "eval", "evalbytes" "exit",
	   "__FILE__", "goto", "last", "__LINE__", "next", "__PACKAGE__", "redo", "return",
	   "sub", "__SUB__", "wantarray"

	   "break" is available only if you enable the experimental "switch" feature or use the
	   "CORE::" prefix. The "switch" feature also enables the "default", "given" and "when"
	   statements, which are documented in "Switch Statements" in perlsyn. The "switch"
	   feature is enabled automatically with a "use v5.10" (or higher) declaration in the
	   current scope. In Perl v5.14 and earlier, "continue" required the "switch" feature,
	   like the other keywords.

	   "evalbytes" is only available with with the "evalbytes" feature (see feature) or if
	   prefixed with "CORE::".  "__SUB__" is only available with with the "current_sub"
	   feature or if prefixed with "CORE::". Both the "evalbytes" and "current_sub" features
	   are enabled automatically with a "use v5.16" (or higher) declaration in the current
	   scope.

       Keywords related to scoping
	   "caller", "import", "local", "my", "our", "package", "state", "use"

	   "state" is available only if the "state" feature is enabled or if it is prefixed with
	   "CORE::".  The "state" feature is enabled automatically with a "use v5.10" (or higher)
	   declaration in the current scope.

       Miscellaneous functions
	   "defined", "formline", "lock", "prototype", "reset", "scalar", "undef"

       Functions for processes and process groups
	   "alarm", "exec", "fork", "getpgrp", "getppid", "getpriority", "kill", "pipe", "qx//",
	   "readpipe", "setpgrp", "setpriority", "sleep", "system", "times", "wait", "waitpid"

       Keywords related to Perl modules
	   "do", "import", "no", "package", "require", "use"

       Keywords related to classes and object-orientation
	   "bless", "dbmclose", "dbmopen", "package", "ref", "tie", "tied", "untie", "use"

       Low-level socket functions
	   "accept", "bind", "connect", "getpeername", "getsockname", "getsockopt", "listen",
	   "recv", "send", "setsockopt", "shutdown", "socket", "socketpair"

       System V interprocess communication functions
	   "msgctl", "msgget", "msgrcv", "msgsnd", "semctl", "semget", "semop", "shmctl",
	   "shmget", "shmread", "shmwrite"

       Fetching user and group info
	   "endgrent", "endhostent", "endnetent", "endpwent", "getgrent", "getgrgid", "getgrnam",
	   "getlogin", "getpwent", "getpwnam", "getpwuid", "setgrent", "setpwent"

       Fetching network info
	   "endprotoent", "endservent", "gethostbyaddr", "gethostbyname", "gethostent",
	   "getnetbyaddr", "getnetbyname", "getnetent", "getprotobyname", "getprotobynumber",
	   "getprotoent", "getservbyname", "getservbyport", "getservent", "sethostent",
	   "setnetent", "setprotoent", "setservent"

       Time-related functions
	   "gmtime", "localtime", "time", "times"

       Non-function keywords
	   "and", "AUTOLOAD", "BEGIN", "CHECK", "cmp", "CORE", "__DATA__", "default", "DESTROY",
	   "else", "elseif", "elsif", "END", "__END__", "eq", "for", "foreach", "ge", "given",
	   "gt", "if", "INIT", "le", "lt", "ne", "not", "or", "UNITCHECK", "unless", "until",
	   "when", "while", "x", "xor"

   Portability
       Perl was born in Unix and can therefore access all common Unix system calls.  In non-Unix
       environments, the functionality of some Unix system calls may not be available or details
       of the available functionality may differ slightly.  The Perl functions affected by this
       are:

       "-X", "binmode", "chmod", "chown", "chroot", "crypt", "dbmclose", "dbmopen", "dump",
       "endgrent", "endhostent", "endnetent", "endprotoent", "endpwent", "endservent", "exec",
       "fcntl", "flock", "fork", "getgrent", "getgrgid", "gethostbyname", "gethostent",
       "getlogin", "getnetbyaddr", "getnetbyname", "getnetent", "getppid", "getpgrp",
       "getpriority", "getprotobynumber", "getprotoent", "getpwent", "getpwnam", "getpwuid",
       "getservbyport", "getservent", "getsockopt", "glob", "ioctl", "kill", "link", "lstat",
       "msgctl", "msgget", "msgrcv", "msgsnd", "open", "pipe", "readlink", "rename", "select",
       "semctl", "semget", "semop", "setgrent", "sethostent", "setnetent", "setpgrp",
       "setpriority", "setprotoent", "setpwent", "setservent", "setsockopt", "shmctl", "shmget",
       "shmread", "shmwrite", "socket", "socketpair", "stat", "symlink", "syscall", "sysopen",
       "system", "times", "truncate", "umask", "unlink", "utime", "wait", "waitpid"

       For more information about the portability of these functions, see perlport and other
       available platform-specific documentation.

   Alphabetical Listing of Perl Functions
       -X FILEHANDLE
       -X EXPR
       -X DIRHANDLE
       -X  A file test, where X is one of the letters listed below.  This unary operator takes
	   one argument, either a filename, a filehandle, or a dirhandle, and tests the
	   associated file to see if something is true about it.  If the argument is omitted,
	   tests $_, except for "-t", which tests STDIN.  Unless otherwise documented, it returns
	   1 for true and '' for false, or the undefined value if the file doesn't exist.
	   Despite the funny names, precedence is the same as any other named unary operator.
	   The operator may be any of:

	       -r  File is readable by effective uid/gid.
	       -w  File is writable by effective uid/gid.
	       -x  File is executable by effective uid/gid.
	       -o  File is owned by effective uid.

	       -R  File is readable by real uid/gid.
	       -W  File is writable by real uid/gid.
	       -X  File is executable by real uid/gid.
	       -O  File is owned by real uid.

	       -e  File exists.
	       -z  File has zero size (is empty).
	       -s  File has nonzero size (returns size in bytes).

	       -f  File is a plain file.
	       -d  File is a directory.
	       -l  File is a symbolic link.
	       -p  File is a named pipe (FIFO), or Filehandle is a pipe.
	       -S  File is a socket.
	       -b  File is a block special file.
	       -c  File is a character special file.
	       -t  Filehandle is opened to a tty.

	       -u  File has setuid bit set.
	       -g  File has setgid bit set.
	       -k  File has sticky bit set.

	       -T  File is an ASCII text file (heuristic guess).
	       -B  File is a "binary" file (opposite of -T).

	       -M  Script start time minus file modification time, in days.
	       -A  Same for access time.
	       -C  Same for inode change time (Unix, may differ for other platforms)

	   Example:

	       while (<>) {
		   chomp;
		   next unless -f $_;  # ignore specials
		   #...
	       }

	   Note that "-s/a/b/" does not do a negated substitution.  Saying "-exp($foo)" still
	   works as expected, however: only single letters following a minus are interpreted as
	   file tests.

	   These operators are exempt from the "looks like a function rule" described above.
	   That is, an opening parenthesis after the operator does not affect how much of the
	   following code constitutes the argument.  Put the opening parentheses before the
	   operator to separate it from code that follows (this applies only to operators with
	   higher precedence than unary operators, of course):

	       -s($file) + 1024   # probably wrong; same as -s($file + 1024)
	       (-s $file) + 1024  # correct

	   The interpretation of the file permission operators "-r", "-R", "-w", "-W", "-x", and
	   "-X" is by default based solely on the mode of the file and the uids and gids of the
	   user.  There may be other reasons you can't actually read, write, or execute the file:
	   for example network filesystem access controls, ACLs (access control lists), read-only
	   filesystems, and unrecognized executable formats.  Note that the use of these six
	   specific operators to verify if some operation is possible is usually a mistake,
	   because it may be open to race conditions.

	   Also note that, for the superuser on the local filesystems, the "-r", "-R", "-w", and
	   "-W" tests always return 1, and "-x" and "-X" return 1 if any execute bit is set in
	   the mode.  Scripts run by the superuser may thus need to do a stat() to determine the
	   actual mode of the file, or temporarily set their effective uid to something else.

	   If you are using ACLs, there is a pragma called "filetest" that may produce more
	   accurate results than the bare stat() mode bits.  When under "use filetest 'access'"
	   the above-mentioned filetests test whether the permission can(not) be granted using
	   the access(2) family of system calls.  Also note that the "-x" and "-X" may under this
	   pragma return true even if there are no execute permission bits set (nor any extra
	   execute permission ACLs).  This strangeness is due to the underlying system calls'
	   definitions.  Note also that, due to the implementation of "use filetest 'access'",
	   the "_" special filehandle won't cache the results of the file tests when this pragma
	   is in effect.  Read the documentation for the "filetest" pragma for more information.

	   The "-T" and "-B" switches work as follows.	The first block or so of the file is
	   examined for odd characters such as strange control codes or characters with the high
	   bit set.  If too many strange characters (>30%) are found, it's a "-B" file; otherwise
	   it's a "-T" file.  Also, any file containing a zero byte in the first block is
	   considered a binary file.  If "-T" or "-B" is used on a filehandle, the current IO
	   buffer is examined rather than the first block.  Both "-T" and "-B" return true on an
	   empty file, or a file at EOF when testing a filehandle.  Because you have to read a
	   file to do the "-T" test, on most occasions you want to use a "-f" against the file
	   first, as in "next unless -f $file && -T $file".

	   If any of the file tests (or either the "stat" or "lstat" operator) is given the
	   special filehandle consisting of a solitary underline, then the stat structure of the
	   previous file test (or stat operator) is used, saving a system call.  (This doesn't
	   work with "-t", and you need to remember that lstat() and "-l" leave values in the
	   stat structure for the symbolic link, not the real file.)  (Also, if the stat buffer
	   was filled by an "lstat" call, "-T" and "-B" will reset it with the results of "stat
	   _").  Example:

	       print "Can do.\n" if -r $a || -w _ || -x _;

	       stat($filename);
	       print "Readable\n" if -r _;
	       print "Writable\n" if -w _;
	       print "Executable\n" if -x _;
	       print "Setuid\n" if -u _;
	       print "Setgid\n" if -g _;
	       print "Sticky\n" if -k _;
	       print "Text\n" if -T _;
	       print "Binary\n" if -B _;

	   As of Perl 5.9.1, as a form of purely syntactic sugar, you can stack file test
	   operators, in a way that "-f -w -x $file" is equivalent to "-x $file && -w _ && -f _".
	   (This is only fancy fancy: if you use the return value of "-f $file" as an argument to
	   another filetest operator, no special magic will happen.)

	   Portability issues: "-X" in perlport.

	   To avoid confusing would-be users of your code with mysterious syntax errors, put
	   something like this at the top of your script:

	       use 5.010;  # so filetest ops can stack

       abs VALUE
       abs Returns the absolute value of its argument.	If VALUE is omitted, uses $_.

       accept NEWSOCKET,GENERICSOCKET
	   Accepts an incoming socket connect, just as accept(2) does.	Returns the packed
	   address if it succeeded, false otherwise.  See the example in "Sockets: Client/Server
	   Communication" in perlipc.

	   On systems that support a close-on-exec flag on files, the flag will be set for the
	   newly opened file descriptor, as determined by the value of $^F.  See "$^F" in
	   perlvar.

       alarm SECONDS
       alarm
	   Arranges to have a SIGALRM delivered to this process after the specified number of
	   wallclock seconds has elapsed.  If SECONDS is not specified, the value stored in $_ is
	   used.  (On some machines, unfortunately, the elapsed time may be up to one second less
	   or more than you specified because of how seconds are counted, and process scheduling
	   may delay the delivery of the signal even further.)

	   Only one timer may be counting at once.  Each call disables the previous timer, and an
	   argument of 0 may be supplied to cancel the previous timer without starting a new one.
	   The returned value is the amount of time remaining on the previous timer.

	   For delays of finer granularity than one second, the Time::HiRes module (from CPAN,
	   and starting from Perl 5.8 part of the standard distribution) provides ualarm().  You
	   may also use Perl's four-argument version of select() leaving the first three
	   arguments undefined, or you might be able to use the "syscall" interface to access
	   setitimer(2) if your system supports it.  See perlfaq8 for details.

	   It is usually a mistake to intermix "alarm" and "sleep" calls, because "sleep" may be
	   internally implemented on your system with "alarm".

	   If you want to use "alarm" to time out a system call you need to use an "eval"/"die"
	   pair.  You can't rely on the alarm causing the system call to fail with $! set to
	   "EINTR" because Perl sets up signal handlers to restart system calls on some systems.
	   Using "eval"/"die" always works, modulo the caveats given in "Signals" in perlipc.

	       eval {
		   local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
		   alarm $timeout;
		   $nread = sysread SOCKET, $buffer, $size;
		   alarm 0;
	       };
	       if ($@) {
		   die unless $@ eq "alarm\n";	 # propagate unexpected errors
		   # timed out
	       }
	       else {
		   # didn't
	       }

	   For more information see perlipc.

	   Portability issues: "alarm" in perlport.

       atan2 Y,X
	   Returns the arctangent of Y/X in the range -PI to PI.

	   For the tangent operation, you may use the "Math::Trig::tan" function, or use the
	   familiar relation:

	       sub tan { sin($_[0]) / cos($_[0])  }

	   The return value for "atan2(0,0)" is implementation-defined; consult your atan2(3)
	   manpage for more information.

	   Portability issues: "atan2" in perlport.

       bind SOCKET,NAME
	   Binds a network address to a socket, just as bind(2) does.  Returns true if it
	   succeeded, false otherwise.	NAME should be a packed address of the appropriate type
	   for the socket.  See the examples in "Sockets: Client/Server Communication" in
	   perlipc.

       binmode FILEHANDLE, LAYER
       binmode FILEHANDLE
	   Arranges for FILEHANDLE to be read or written in "binary" or "text" mode on systems
	   where the run-time libraries distinguish between binary and text files.  If FILEHANDLE
	   is an expression, the value is taken as the name of the filehandle.	Returns true on
	   success, otherwise it returns "undef" and sets $! (errno).

	   On some systems (in general, DOS- and Windows-based systems) binmode() is necessary
	   when you're not working with a text file.  For the sake of portability it is a good
	   idea always to use it when appropriate, and never to use it when it isn't appropriate.
	   Also, people can set their I/O to be by default UTF8-encoded Unicode, not bytes.

	   In other words: regardless of platform, use binmode() on binary data, like images, for
	   example.

	   If LAYER is present it is a single string, but may contain multiple directives.  The
	   directives alter the behaviour of the filehandle.  When LAYER is present, using
	   binmode on a text file makes sense.

	   If LAYER is omitted or specified as ":raw" the filehandle is made suitable for passing
	   binary data.  This includes turning off possible CRLF translation and marking it as
	   bytes (as opposed to Unicode characters).  Note that, despite what may be implied in
	   "Programming Perl" (the Camel, 3rd edition) or elsewhere, ":raw" is not simply the
	   inverse of ":crlf".	Other layers that would affect the binary nature of the stream
	   are also disabled.  See PerlIO, perlrun, and the discussion about the PERLIO
	   environment variable.

	   The ":bytes", ":crlf", ":utf8", and any other directives of the form ":...", are
	   called I/O layers.  The "open" pragma can be used to establish default I/O layers.
	   See open.

	   The LAYER parameter of the binmode() function is described as "DISCIPLINE" in
	   "Programming Perl, 3rd Edition".  However, since the publishing of this book, by many
	   known as "Camel III", the consensus of the naming of this functionality has moved from
	   "discipline" to "layer".  All documentation of this version of Perl therefore refers
	   to "layers" rather than to "disciplines".  Now back to the regularly scheduled
	   documentation...

	   To mark FILEHANDLE as UTF-8, use ":utf8" or ":encoding(UTF-8)".  ":utf8" just marks
	   the data as UTF-8 without further checking, while ":encoding(UTF-8)" checks the data
	   for actually being valid UTF-8.  More details can be found in PerlIO::encoding.

	   In general, binmode() should be called after open() but before any I/O is done on the
	   filehandle.	Calling binmode() normally flushes any pending buffered output data (and
	   perhaps pending input data) on the handle.  An exception to this is the ":encoding"
	   layer that changes the default character encoding of the handle; see "open".  The
	   ":encoding" layer sometimes needs to be called in mid-stream, and it doesn't flush the
	   stream.  The ":encoding" also implicitly pushes on top of itself the ":utf8" layer
	   because internally Perl operates on UTF8-encoded Unicode characters.

	   The operating system, device drivers, C libraries, and Perl run-time system all
	   conspire to let the programmer treat a single character ("\n") as the line terminator,
	   irrespective of external representation.  On many operating systems, the native text
	   file representation matches the internal representation, but on some platforms the
	   external representation of "\n" is made up of more than one character.

	   All variants of Unix, Mac OS (old and new), and Stream_LF files on VMS use a single
	   character to end each line in the external representation of text (even though that
	   single character is CARRIAGE RETURN on old, pre-Darwin flavors of Mac OS, and is LINE
	   FEED on Unix and most VMS files).  In other systems like OS/2, DOS, and the various
	   flavors of MS-Windows, your program sees a "\n" as a simple "\cJ", but what's stored
	   in text files are the two characters "\cM\cJ".  That means that if you don't use
	   binmode() on these systems, "\cM\cJ" sequences on disk will be converted to "\n" on
	   input, and any "\n" in your program will be converted back to "\cM\cJ" on output.
	   This is what you want for text files, but it can be disastrous for binary files.

	   Another consequence of using binmode() (on some systems) is that special end-of-file
	   markers will be seen as part of the data stream.  For systems from the Microsoft
	   family this means that, if your binary data contain "\cZ", the I/O subsystem will
	   regard it as the end of the file, unless you use binmode().

	   binmode() is important not only for readline() and print() operations, but also when
	   using read(), seek(), sysread(), syswrite() and tell() (see perlport for more
	   details).  See the $/ and "$\" variables in perlvar for how to manually set your input
	   and output line-termination sequences.

	   Portability issues: "binmode" in perlport.

       bless REF,CLASSNAME
       bless REF
	   This function tells the thingy referenced by REF that it is now an object in the
	   CLASSNAME package.  If CLASSNAME is omitted, the current package is used.  Because a
	   "bless" is often the last thing in a constructor, it returns the reference for
	   convenience.  Always use the two-argument version if a derived class might inherit the
	   function doing the blessing.  Seeperlobj for more about the blessing (and blessings)
	   of objects.

	   Consider always blessing objects in CLASSNAMEs that are mixed case.	Namespaces with
	   all lowercase names are considered reserved for Perl pragmata.  Builtin types have all
	   uppercase names.  To prevent confusion, you may wish to avoid such package names as
	   well.  Make sure that CLASSNAME is a true value.

	   See "Perl Modules" in perlmod.

       break
	   Break out of a "given()" block.

	   This keyword is enabled by the "switch" feature: see feature for more information.
	   You can also access it by prefixing it with "CORE::".  Alternately, include a "use
	   v5.10" or later to the current scope.

       caller EXPR
       caller
	   Returns the context of the current subroutine call.	In scalar context, returns the
	   caller's package name if there is a caller (that is, if we're in a subroutine or
	   "eval" or "require") and the undefined value otherwise.  In list context, returns

	       # 0	   1	      2
	       ($package, $filename, $line) = caller;

	   With EXPR, it returns some extra information that the debugger uses to print a stack
	   trace.  The value of EXPR indicates how many call frames to go back before the current
	   one.

	       #  0	    1	       2      3 	   4
	       ($package, $filename, $line, $subroutine, $hasargs,

	       #  5	     6		7	     8	     9	       10
	       $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash)
		= caller($i);

	   Here $subroutine may be "(eval)" if the frame is not a subroutine call, but an "eval".
	   In such a case additional elements $evaltext and $is_require are set: $is_require is
	   true if the frame is created by a "require" or "use" statement, $evaltext contains the
	   text of the "eval EXPR" statement.  In particular, for an "eval BLOCK" statement,
	   $subroutine is "(eval)", but $evaltext is undefined.  (Note also that each "use"
	   statement creates a "require" frame inside an "eval EXPR" frame.)  $subroutine may
	   also be "(unknown)" if this particular subroutine happens to have been deleted from
	   the symbol table.  $hasargs is true if a new instance of @_ was set up for the frame.
	   $hints and $bitmask contain pragmatic hints that the caller was compiled with.  The
	   $hints and $bitmask values are subject to change between versions of Perl, and are not
	   meant for external use.

	   $hinthash is a reference to a hash containing the value of "%^H" when the caller was
	   compiled, or "undef" if "%^H" was empty.  Do not modify the values of this hash, as
	   they are the actual values stored in the optree.

	   Furthermore, when called from within the DB package in list context, and with an
	   argument, caller returns more detailed information: it sets the list variable
	   @DB::args to be the arguments with which the subroutine was invoked.

	   Be aware that the optimizer might have optimized call frames away before "caller" had
	   a chance to get the information.  That means that caller(N) might not return
	   information about the call frame you expect it to, for "N > 1".  In particular,
	   @DB::args might have information from the previous time "caller" was called.

	   Be aware that setting @DB::args is best effort, intended for debugging or generating
	   backtraces, and should not be relied upon.  In particular, as @_ contains aliases to
	   the caller's arguments, Perl does not take a copy of @_, so @DB::args will contain
	   modifications the subroutine makes to @_ or its contents, not the original values at
	   call time.  @DB::args, like @_, does not hold explicit references to its elements, so
	   under certain cases its elements may have become freed and reallocated for other
	   variables or temporary values.  Finally, a side effect of the current implementation
	   is that the effects of "shift @_" can normally be undone (but not "pop @_" or other
	   splicing, and not if a reference to @_ has been taken, and subject to the caveat about
	   reallocated elements), so @DB::args is actually a hybrid of the current state and
	   initial state of @_.  Buyer beware.

       chdir EXPR
       chdir FILEHANDLE
       chdir DIRHANDLE
       chdir
	   Changes the working directory to EXPR, if possible.	If EXPR is omitted, changes to
	   the directory specified by $ENV{HOME}, if set; if not, changes to the directory
	   specified by $ENV{LOGDIR}.  (Under VMS, the variable $ENV{SYS$LOGIN} is also checked,
	   and used if it is set.)  If neither is set, "chdir" does nothing.  It returns true on
	   success, false otherwise.  See the example under "die".

	   On systems that support fchdir(2), you may pass a filehandle or directory handle as
	   the argument.  On systems that don't support fchdir(2), passing handles raises an
	   exception.

       chmod LIST
	   Changes the permissions of a list of files.	The first element of the list must be the
	   numeric mode, which should probably be an octal number, and which definitely should
	   not be a string of octal digits: 0644 is okay, but "0644" is not.  Returns the number
	   of files successfully changed.  See also "oct" if all you have is a string.

	       $cnt = chmod 0755, "foo", "bar";
	       chmod 0755, @executables;
	       $mode = "0644"; chmod $mode, "foo";	# !!! sets mode to
							# --w----r-T
	       $mode = "0644"; chmod oct($mode), "foo"; # this is better
	       $mode = 0644;   chmod $mode, "foo";	# this is best

	   On systems that support fchmod(2), you may pass filehandles among the files.  On
	   systems that don't support fchmod(2), passing filehandles raises an exception.
	   Filehandles must be passed as globs or glob references to be recognized; barewords are
	   considered filenames.

	       open(my $fh, "<", "foo");
	       my $perm = (stat $fh)[2] & 07777;
	       chmod($perm | 0600, $fh);

	   You can also import the symbolic "S_I*" constants from the "Fcntl" module:

	       use Fcntl qw( :mode );
	       chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables;
	       # Identical to the chmod 0755 of the example above.

	   Portability issues: "chmod" in perlport.

       chomp VARIABLE
       chomp( LIST )
       chomp
	   This safer version of "chop" removes any trailing string that corresponds to the
	   current value of $/ (also known as $INPUT_RECORD_SEPARATOR in the "English" module).
	   It returns the total number of characters removed from all its arguments.  It's often
	   used to remove the newline from the end of an input record when you're worried that
	   the final record may be missing its newline.  When in paragraph mode ("$/ = """), it
	   removes all trailing newlines from the string.  When in slurp mode ("$/ = undef") or
	   fixed-length record mode ($/ is a reference to an integer or the like; see perlvar)
	   chomp() won't remove anything.  If VARIABLE is omitted, it chomps $_.  Example:

	       while (<>) {
		   chomp;  # avoid \n on last field
		   @array = split(/:/);
		   # ...
	       }

	   If VARIABLE is a hash, it chomps the hash's values, but not its keys.

	   You can actually chomp anything that's an lvalue, including an assignment:

	       chomp($cwd = `pwd`);
	       chomp($answer = <STDIN>);

	   If you chomp a list, each element is chomped, and the total number of characters
	   removed is returned.

	   Note that parentheses are necessary when you're chomping anything that is not a simple
	   variable.  This is because "chomp $cwd = `pwd`;" is interpreted as "(chomp $cwd) =
	   `pwd`;", rather than as "chomp( $cwd = `pwd` )" which you might expect.  Similarly,
	   "chomp $a, $b" is interpreted as "chomp($a), $b" rather than as "chomp($a, $b)".

       chop VARIABLE
       chop( LIST )
       chop
	   Chops off the last character of a string and returns the character chopped.	It is
	   much more efficient than "s/.$//s" because it neither scans nor copies the string.  If
	   VARIABLE is omitted, chops $_.  If VARIABLE is a hash, it chops the hash's values, but
	   not its keys.

	   You can actually chop anything that's an lvalue, including an assignment.

	   If you chop a list, each element is chopped.  Only the value of the last "chop" is
	   returned.

	   Note that "chop" returns the last character.  To return all but the last character,
	   use "substr($string, 0, -1)".

	   See also "chomp".

       chown LIST
	   Changes the owner (and group) of a list of files.  The first two elements of the list
	   must be the numeric uid and gid, in that order.  A value of -1 in either position is
	   interpreted by most systems to leave that value unchanged.  Returns the number of
	   files successfully changed.

	       $cnt = chown $uid, $gid, 'foo', 'bar';
	       chown $uid, $gid, @filenames;

	   On systems that support fchown(2), you may pass filehandles among the files.  On
	   systems that don't support fchown(2), passing filehandles raises an exception.
	   Filehandles must be passed as globs or glob references to be recognized; barewords are
	   considered filenames.

	   Here's an example that looks up nonnumeric uids in the passwd file:

	       print "User: ";
	       chomp($user = <STDIN>);
	       print "Files: ";
	       chomp($pattern = <STDIN>);

	       ($login,$pass,$uid,$gid) = getpwnam($user)
		   or die "$user not in passwd file";

	       @ary = glob($pattern);  # expand filenames
	       chown $uid, $gid, @ary;

	   On most systems, you are not allowed to change the ownership of the file unless you're
	   the superuser, although you should be able to change the group to any of your
	   secondary groups.  On insecure systems, these restrictions may be relaxed, but this is
	   not a portable assumption.  On POSIX systems, you can detect this condition this way:

	       use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
	       $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);

	   Portability issues: "chmod" in perlport.

       chr NUMBER
       chr Returns the character represented by that NUMBER in the character set.  For example,
	   "chr(65)" is "A" in either ASCII or Unicode, and chr(0x263a) is a Unicode smiley face.

	   Negative values give the Unicode replacement character (chr(0xfffd)), except under the
	   bytes pragma, where the low eight bits of the value (truncated to an integer) are
	   used.

	   If NUMBER is omitted, uses $_.

	   For the reverse, use "ord".

	   Note that characters from 128 to 255 (inclusive) are by default internally not encoded
	   as UTF-8 for backward compatibility reasons.

	   See perlunicode for more about Unicode.

       chroot FILENAME
       chroot
	   This function works like the system call by the same name: it makes the named
	   directory the new root directory for all further pathnames that begin with a "/" by
	   your process and all its children.  (It doesn't change your current working directory,
	   which is unaffected.)  For security reasons, this call is restricted to the superuser.
	   If FILENAME is omitted, does a "chroot" to $_.

	   Portability issues: "chroot" in perlport.

       close FILEHANDLE
       close
	   Closes the file or pipe associated with the filehandle, flushes the IO buffers, and
	   closes the system file descriptor.  Returns true if those operations succeed and if no
	   error was reported by any PerlIO layer.  Closes the currently selected filehandle if
	   the argument is omitted.

	   You don't have to close FILEHANDLE if you are immediately going to do another "open"
	   on it, because "open" closes it for you.  (See open.)  However, an explicit "close" on
	   an input file resets the line counter ($.), while the implicit close done by "open"
	   does not.

	   If the filehandle came from a piped open, "close" returns false if one of the other
	   syscalls involved fails or if its program exits with non-zero status.  If the only
	   problem was that the program exited non-zero, $!  will be set to 0.	Closing a pipe
	   also waits for the process executing on the pipe to exit--in case you wish to look at
	   the output of the pipe afterwards--and implicitly puts the exit status value of that
	   command into $? and "${^CHILD_ERROR_NATIVE}".

	   If there are multiple threads running, "close" on a filehandle from a piped open
	   returns true without waiting for the child process to terminate, if the filehandle is
	   still open in another thread.

	   Closing the read end of a pipe before the process writing to it at the other end is
	   done writing results in the writer receiving a SIGPIPE.  If the other end can't handle
	   that, be sure to read all the data before closing the pipe.

	   Example:

	       open(OUTPUT, '|sort >foo')  # pipe to sort
		   or die "Can't start sort: $!";
	       #...			   # print stuff to output
	       close OUTPUT		   # wait for sort to finish
		   or warn $! ? "Error closing sort pipe: $!"
			      : "Exit status $? from sort";
	       open(INPUT, 'foo')	   # get sort's results
		   or die "Can't open 'foo' for input: $!";

	   FILEHANDLE may be an expression whose value can be used as an indirect filehandle,
	   usually the real filehandle name or an autovivified handle.

       closedir DIRHANDLE
	   Closes a directory opened by "opendir" and returns the success of that system call.

       connect SOCKET,NAME
	   Attempts to connect to a remote socket, just like connect(2).  Returns true if it
	   succeeded, false otherwise.	NAME should be a packed address of the appropriate type
	   for the socket.  See the examples in "Sockets: Client/Server Communication" in
	   perlipc.

       continue BLOCK
       continue
	   When followed by a BLOCK, "continue" is actually a flow control statement rather than
	   a function.	If there is a "continue" BLOCK attached to a BLOCK (typically in a
	   "while" or "foreach"), it is always executed just before the conditional is about to
	   be evaluated again, just like the third part of a "for" loop in C.  Thus it can be
	   used to increment a loop variable, even when the loop has been continued via the
	   "next" statement (which is similar to the C "continue" statement).

	   "last", "next", or "redo" may appear within a "continue" block; "last" and "redo"
	   behave as if they had been executed within the main block.  So will "next", but since
	   it will execute a "continue" block, it may be more entertaining.

	       while (EXPR) {
		   ### redo always comes here
		   do_something;
	       } continue {
		   ### next always comes here
		   do_something_else;
		   # then back the top to re-check EXPR
	       }
	       ### last always comes here

	   Omitting the "continue" section is equivalent to using an empty one, logically enough,
	   so "next" goes directly back to check the condition at the top of the loop.

	   When there is no BLOCK, "continue" is a function that falls through the current "when"
	   or "default" block instead of iterating a dynamically enclosing "foreach" or exiting a
	   lexically enclosing "given".  In Perl 5.14 and earlier, this form of "continue" was
	   only available when the "switch" feature was enabled.  See feature and "Switch
	   Statements" in perlsyn for more information.

       cos EXPR
       cos Returns the cosine of EXPR (expressed in radians).  If EXPR is omitted, takes the
	   cosine of $_.

	   For the inverse cosine operation, you may use the "Math::Trig::acos()" function, or
	   use this relation:

	       sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }

       crypt PLAINTEXT,SALT
	   Creates a digest string exactly like the crypt(3) function in the C library (assuming
	   that you actually have a version there that has not been extirpated as a potential
	   munition).

	   crypt() is a one-way hash function.	The PLAINTEXT and SALT are turned into a short
	   string, called a digest, which is returned.	The same PLAINTEXT and SALT will always
	   return the same string, but there is no (known) way to get the original PLAINTEXT from
	   the hash.  Small changes in the PLAINTEXT or SALT will result in large changes in the
	   digest.

	   There is no decrypt function.  This function isn't all that useful for cryptography
	   (for that, look for Crypt modules on your nearby CPAN mirror) and the name "crypt" is
	   a bit of a misnomer.  Instead it is primarily used to check if two pieces of text are
	   the same without having to transmit or store the text itself.  An example is checking
	   if a correct password is given.  The digest of the password is stored, not the
	   password itself.  The user types in a password that is crypt()'d with the same salt as
	   the stored digest.  If the two digests match, the password is correct.

	   When verifying an existing digest string you should use the digest as the salt (like
	   "crypt($plain, $digest) eq $digest").  The SALT used to create the digest is visible
	   as part of the digest.  This ensures crypt() will hash the new string with the same
	   salt as the digest.	This allows your code to work with the standard crypt and with
	   more exotic implementations.  In other words, assume nothing about the returned string
	   itself nor about how many bytes of SALT may matter.

	   Traditionally the result is a string of 13 bytes: two first bytes of the salt,
	   followed by 11 bytes from the set "[./0-9A-Za-z]", and only the first eight bytes of
	   PLAINTEXT mattered.	But alternative hashing schemes (like MD5), higher level security
	   schemes (like C2), and implementations on non-Unix platforms may produce different
	   strings.

	   When choosing a new salt create a random two character string whose characters come
	   from the set "[./0-9A-Za-z]" (like "join '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand
	   64, rand 64]").  This set of characters is just a recommendation; the characters
	   allowed in the salt depend solely on your system's crypt library, and Perl can't
	   restrict what salts "crypt()" accepts.

	   Here's an example that makes sure that whoever runs this program knows their password:

	       $pwd = (getpwuid($<))[1];

	       system "stty -echo";
	       print "Password: ";
	       chomp($word = <STDIN>);
	       print "\n";
	       system "stty echo";

	       if (crypt($word, $pwd) ne $pwd) {
		   die "Sorry...\n";
	       } else {
		   print "ok\n";
	       }

	   Of course, typing in your own password to whoever asks you for it is unwise.

	   The crypt function is unsuitable for hashing large quantities of data, not least of
	   all because you can't get the information back.  Look at the Digest module for more
	   robust algorithms.

	   If using crypt() on a Unicode string (which potentially has characters with codepoints
	   above 255), Perl tries to make sense of the situation by trying to downgrade (a copy
	   of) the string back to an eight-bit byte string before calling crypt() (on that copy).
	   If that works, good.  If not, crypt() dies with "Wide character in crypt".

	   Portability issues: "crypt" in perlport.

       dbmclose HASH
	   [This function has been largely superseded by the "untie" function.]

	   Breaks the binding between a DBM file and a hash.

	   Portability issues: "dbmclose" in perlport.

       dbmopen HASH,DBNAME,MASK
	   [This function has been largely superseded by the tie function.]

	   This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a hash.  HASH
	   is the name of the hash.  (Unlike normal "open", the first argument is not a
	   filehandle, even though it looks like one).	DBNAME is the name of the database
	   (without the .dir or .pag extension if any).  If the database does not exist, it is
	   created with protection specified by MASK (as modified by the "umask").  To prevent
	   creation of the database if it doesn't exist, you may specify a MODE of 0, and the
	   function will return a false value if it can't find an existing database.  If your
	   system supports only the older DBM functions, you may make only one "dbmopen" call in
	   your program.  In older versions of Perl, if your system had neither DBM nor ndbm,
	   calling "dbmopen" produced a fatal error; it now falls back to sdbm(3).

	   If you don't have write access to the DBM file, you can only read hash variables, not
	   set them.  If you want to test whether you can write, either use file tests or try
	   setting a dummy hash entry inside an "eval" to trap the error.

	   Note that functions such as "keys" and "values" may return huge lists when used on
	   large DBM files.  You may prefer to use the "each" function to iterate over large DBM
	   files.  Example:

	       # print out history file offsets
	       dbmopen(%HIST,'/usr/lib/news/history',0666);
	       while (($key,$val) = each %HIST) {
		   print $key, ' = ', unpack('L',$val), "\n";
	       }
	       dbmclose(%HIST);

	   See also AnyDBM_File for a more general description of the pros and cons of the
	   various dbm approaches, as well as DB_File for a particularly rich implementation.

	   You can control which DBM library you use by loading that library before you call
	   dbmopen():

	       use DB_File;
	       dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
		   or die "Can't open netscape history file: $!";

	   Portability issues: "dbmopen" in perlport.

       defined EXPR
       defined
	   Returns a Boolean value telling whether EXPR has a value other than the undefined
	   value "undef".  If EXPR is not present, $_ is checked.

	   Many operations return "undef" to indicate failure, end of file, system error,
	   uninitialized variable, and other exceptional conditions.  This function allows you to
	   distinguish "undef" from other values.  (A simple Boolean test will not distinguish
	   among "undef", zero, the empty string, and "0", which are all equally false.)  Note
	   that since "undef" is a valid scalar, its presence doesn't necessarily indicate an
	   exceptional condition: "pop" returns "undef" when its argument is an empty array, or
	   when the element to return happens to be "undef".

	   You may also use "defined(&func)" to check whether subroutine &func has ever been
	   defined.  The return value is unaffected by any forward declarations of &func.  A
	   subroutine that is not defined may still be callable: its package may have an
	   "AUTOLOAD" method that makes it spring into existence the first time that it is
	   called; see perlsub.

	   Use of "defined" on aggregates (hashes and arrays) is deprecated.  It used to report
	   whether memory for that aggregate had ever been allocated.  This behavior may
	   disappear in future versions of Perl.  You should instead use a simple test for size:

	       if (@an_array) { print "has array elements\n" }
	       if (%a_hash)   { print "has hash members\n"   }

	   When used on a hash element, it tells you whether the value is defined, not whether
	   the key exists in the hash.	Use "exists" for the latter purpose.

	   Examples:

	       print if defined $switch{D};
	       print "$val\n" while defined($val = pop(@ary));
	       die "Can't readlink $sym: $!"
		   unless defined($value = readlink $sym);
	       sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
	       $debugging = 0 unless defined $debugging;

	   Note:  Many folks tend to overuse "defined" and are then surprised to discover that
	   the number 0 and "" (the zero-length string) are, in fact, defined values.  For
	   example, if you say

	       "ab" =~ /a(.*)b/;

	   The pattern match succeeds and $1 is defined, although it matched "nothing".  It
	   didn't really fail to match anything.  Rather, it matched something that happened to
	   be zero characters long.  This is all very above-board and honest.  When a function
	   returns an undefined value, it's an admission that it couldn't give you an honest
	   answer.  So you should use "defined" only when questioning the integrity of what
	   you're trying to do.  At other times, a simple comparison to 0 or "" is what you want.

	   See also "undef", "exists", "ref".

       delete EXPR
	   Given an expression that specifies an element or slice of a hash, "delete" deletes the
	   specified elements from that hash so that exists() on that element no longer returns
	   true.  Setting a hash element to the undefined value does not remove its key, but
	   deleting it does; see "exists".

	   In list context, returns the value or values deleted, or the last such element in
	   scalar context.  The return list's length always matches that of the argument list:
	   deleting non-existent elements returns the undefined value in their corresponding
	   positions.

	   delete() may also be used on arrays and array slices, but its behavior is less
	   straightforward.  Although exists() will return false for deleted entries, deleting
	   array elements never changes indices of existing values; use shift() or splice() for
	   that.  However, if all deleted elements fall at the end of an array, the array's size
	   shrinks to the position of the highest element that still tests true for exists(), or
	   to 0 if none do.

	   WARNING: Calling delete on array values is deprecated and likely to be removed in a
	   future version of Perl.

	   Deleting from %ENV modifies the environment.  Deleting from a hash tied to a DBM file
	   deletes the entry from the DBM file.  Deleting from a "tied" hash or array may not
	   necessarily return anything; it depends on the implementation of the "tied" package's
	   DELETE method, which may do whatever it pleases.

	   The "delete local EXPR" construct localizes the deletion to the current block at run
	   time.  Until the block exits, elements locally deleted temporarily no longer exist.
	   See "Localized deletion of elements of composite types" in perlsub.

	       %hash = (foo => 11, bar => 22, baz => 33);
	       $scalar = delete $hash{foo};		# $scalar is 11
	       $scalar = delete @hash{qw(foo bar)};	# $scalar is 22
	       @array  = delete @hash{qw(foo bar baz)}; # @array  is (undef,undef,33)

	   The following (inefficiently) deletes all the values of %HASH and @ARRAY:

	       foreach $key (keys %HASH) {
		   delete $HASH{$key};
	       }

	       foreach $index (0 .. $#ARRAY) {
		   delete $ARRAY[$index];
	       }

	   And so do these:

	       delete @HASH{keys %HASH};

	       delete @ARRAY[0 .. $#ARRAY];

	   But both are slower than assigning the empty list or undefining %HASH or @ARRAY, which
	   is the customary way to empty out an aggregate:

	       %HASH = ();     # completely empty %HASH
	       undef %HASH;    # forget %HASH ever existed

	       @ARRAY = ();    # completely empty @ARRAY
	       undef @ARRAY;   # forget @ARRAY ever existed

	   The EXPR can be arbitrarily complicated provided its final operation is an element or
	   slice of an aggregate:

	       delete $ref->[$x][$y]{$key};
	       delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};

	       delete $ref->[$x][$y][$index];
	       delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];

       die LIST
	   "die" raises an exception.  Inside an "eval" the error message is stuffed into $@ and
	   the "eval" is terminated with the undefined value.  If the exception is outside of all
	   enclosing "eval"s, then the uncaught exception prints LIST to "STDERR" and exits with
	   a non-zero value.  If you need to exit the process with a specific exit code, see
	   "exit".

	   Equivalent examples:

	       die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
	       chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"

	   If the last element of LIST does not end in a newline, the current script line number
	   and input line number (if any) are also printed, and a newline is supplied.	Note that
	   the "input line number" (also known as "chunk") is subject to whatever notion of
	   "line" happens to be currently in effect, and is also available as the special
	   variable $..  See "$/" in perlvar and "$." in perlvar.

	   Hint: sometimes appending ", stopped" to your message will cause it to make better
	   sense when the string "at foo line 123" is appended.  Suppose you are running script
	   "canasta".

	       die "/etc/games is no good";
	       die "/etc/games is no good, stopped";

	   produce, respectively

	       /etc/games is no good at canasta line 123.
	       /etc/games is no good, stopped at canasta line 123.

	   If the output is empty and $@ already contains a value (typically from a previous
	   eval) that value is reused after appending "\t...propagated".  This is useful for
	   propagating exceptions:

	       eval { ... };
	       die unless $@ =~ /Expected exception/;

	   If the output is empty and $@ contains an object reference that has a "PROPAGATE"
	   method, that method will be called with additional file and line number parameters.
	   The return value replaces the value in $@;  i.e., as if "$@ = eval {
	   $@->PROPAGATE(__FILE__, __LINE__) };" were called.

	   If $@ is empty then the string "Died" is used.

	   If an uncaught exception results in interpreter exit, the exit code is determined from
	   the values of $! and $? with this pseudocode:

	       exit $! if $!;		   # errno
	       exit $? >> 8 if $? >> 8;    # child exit status
	       exit 255;		   # last resort

	   The intent is to squeeze as much possible information about the likely cause into the
	   limited space of the system exit code.  However, as $! is the value of C's "errno",
	   which can be set by any system call, this means that the value of the exit code used
	   by "die" can be non-predictable, so should not be relied upon, other than to be non-
	   zero.

	   You can also call "die" with a reference argument, and if this is trapped within an
	   "eval", $@ contains that reference.	This permits more elaborate exception handling
	   using objects that maintain arbitrary state about the exception.  Such a scheme is
	   sometimes preferable to matching particular string values of $@ with regular
	   expressions.  Because $@ is a global variable and "eval" may be used within object
	   implementations, be careful that analyzing the error object doesn't replace the
	   reference in the global variable.  It's easiest to make a local copy of the reference
	   before any manipulations.  Here's an example:

	       use Scalar::Util "blessed";

	       eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
	       if (my $ev_err = $@) {
		   if (blessed($ev_err) && $ev_err->isa("Some::Module::Exception")) {
		       # handle Some::Module::Exception
		   }
		   else {
		       # handle all other possible exceptions
		   }
	       }

	   Because Perl stringifies uncaught exception messages before display, you'll probably
	   want to overload stringification operations on exception objects.  See overload for
	   details about that.

	   You can arrange for a callback to be run just before the "die" does its deed, by
	   setting the $SIG{__DIE__} hook.  The associated handler is called with the error text
	   and can change the error message, if it sees fit, by calling "die" again.  See "%SIG"
	   in perlvar for details on setting %SIG entries, and "eval BLOCK" for some examples.
	   Although this feature was to be run only right before your program was to exit, this
	   is not currently so: the $SIG{__DIE__} hook is currently called even inside eval()ed
	   blocks/strings!  If one wants the hook to do nothing in such situations, put

	       die @_ if $^S;

	   as the first line of the handler (see "$^S" in perlvar).  Because this promotes
	   strange action at a distance, this counterintuitive behavior may be fixed in a future
	   release.

	   See also exit(), warn(), and the Carp module.

       do BLOCK
	   Not really a function.  Returns the value of the last command in the sequence of
	   commands indicated by BLOCK.  When modified by the "while" or "until" loop modifier,
	   executes the BLOCK once before testing the loop condition.  (On other statements the
	   loop modifiers test the conditional first.)

	   "do BLOCK" does not count as a loop, so the loop control statements "next", "last", or
	   "redo" cannot be used to leave or restart the block.  See perlsyn for alternative
	   strategies.

       do SUBROUTINE(LIST)
	   This form of subroutine call is deprecated.	SUBROUTINE can be a bareword, a scalar
	   variable or a subroutine beginning with "&".

       do EXPR
	   Uses the value of EXPR as a filename and executes the contents of the file as a Perl
	   script.

	       do 'stat.pl';

	   is just like

	       eval `cat stat.pl`;

	   except that it's more efficient and concise, keeps track of the current filename for
	   error messages, searches the @INC directories, and updates %INC if the file is found.
	   See "@INC" in perlvar and "%INC" in perlvar for these variables.  It also differs in
	   that code evaluated with "do FILENAME" cannot see lexicals in the enclosing scope;
	   "eval STRING" does.	It's the same, however, in that it does reparse the file every
	   time you call it, so you probably don't want to do this inside a loop.

	   If "do" can read the file but cannot compile it, it returns "undef" and sets an error
	   message in $@.  If "do" cannot read the file, it returns undef and sets $! to the
	   error.  Always check $@ first, as compilation could fail in a way that also sets $!.
	   If the file is successfully compiled, "do" returns the value of the last expression
	   evaluated.

	   Inclusion of library modules is better done with the "use" and "require" operators,
	   which also do automatic error checking and raise an exception if there's a problem.

	   You might like to use "do" to read in a program configuration file.	Manual error
	   checking can be done this way:

	       # read in config files: system first, then user
	       for $file ("/share/prog/defaults.rc",
			  "$ENV{HOME}/.someprogrc")
	       {
		   unless ($return = do $file) {
		       warn "couldn't parse $file: $@" if $@;
		       warn "couldn't do $file: $!"    unless defined $return;
		       warn "couldn't run $file"       unless $return;
		   }
	       }

       dump LABEL
       dump
	   This function causes an immediate core dump.  See also the -u command-line switch in
	   perlrun, which does the same thing.	Primarily this is so that you can use the undump
	   program (not supplied) to turn your core dump into an executable binary after having
	   initialized all your variables at the beginning of the program.  When the new binary
	   is executed it will begin by executing a "goto LABEL" (with all the restrictions that
	   "goto" suffers).  Think of it as a goto with an intervening core dump and
	   reincarnation.  If "LABEL" is omitted, restarts the program from the top.

	   WARNING: Any files opened at the time of the dump will not be open any more when the
	   program is reincarnated, with possible resulting confusion by Perl.

	   This function is now largely obsolete, mostly because it's very hard to convert a core
	   file into an executable.  That's why you should now invoke it as "CORE::dump()", if
	   you don't want to be warned against a possible typo.

	   Portability issues: "dump" in perlport.

       each HASH
       each ARRAY
       each EXPR
	   When called on a hash in list context, returns a 2-element list consisting of the key
	   and value for the next element of a hash.  In Perl 5.12 and later only, it will also
	   return the index and value for the next element of an array so that you can iterate
	   over it; older Perls consider this a syntax error.  When called in scalar context,
	   returns only the key (not the value) in a hash, or the index in an array.

	   Hash entries are returned in an apparently random order.  The actual random order is
	   subject to change in future versions of Perl, but it is guaranteed to be in the same
	   order as either the "keys" or "values" function would produce on the same (unmodified)
	   hash.  Since Perl 5.8.2 the ordering can be different even between different runs of
	   Perl for security reasons (see "Algorithmic Complexity Attacks" in perlsec).

	   After "each" has returned all entries from the hash or array, the next call to "each"
	   returns the empty list in list context and "undef" in scalar context; the next call
	   following that one restarts iteration.  Each hash or array has its own internal
	   iterator, accessed by "each", "keys", and "values".	The iterator is implicitly reset
	   when "each" has reached the end as just described; it can be explicitly reset by
	   calling "keys" or "values" on the hash or array.  If you add or delete a hash's
	   elements while iterating over it, entries may be skipped or duplicated--so don't do
	   that.  Exception: In the current implementation, it is always safe to delete the item
	   most recently returned by "each()", so the following code works properly:

		   while (($key, $value) = each %hash) {
		     print $key, "\n";
		     delete $hash{$key};   # This is safe
		   }

	   This prints out your environment like the printenv(1) program, but in a different
	   order:

	       while (($key,$value) = each %ENV) {
		   print "$key=$value\n";
	       }

	   Starting with Perl 5.14, "each" can take a scalar EXPR, which must hold reference to
	   an unblessed hash or array.	The argument will be dereferenced automatically.  This
	   aspect of "each" is considered highly experimental.	The exact behaviour may change in
	   a future version of Perl.

	       while (($key,$value) = each $hashref) { ... }

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.012;  # so keys/values/each work on arrays
	       use 5.014;  # so keys/values/each work on scalars (experimental)

	   See also "keys", "values", and "sort".

       eof FILEHANDLE
       eof ()
       eof Returns 1 if the next read on FILEHANDLE will return end of file or if FILEHANDLE is
	   not open.  FILEHANDLE may be an expression whose value gives the real filehandle.
	   (Note that this function actually reads a character and then "ungetc"s it, so isn't
	   useful in an interactive context.)  Do not read from a terminal file (or call
	   "eof(FILEHANDLE)" on it) after end-of-file is reached.  File types such as terminals
	   may lose the end-of-file condition if you do.

	   An "eof" without an argument uses the last file read.  Using "eof()" with empty
	   parentheses is different.  It refers to the pseudo file formed from the files listed
	   on the command line and accessed via the "<>" operator.  Since "<>" isn't explicitly
	   opened, as a normal filehandle is, an "eof()" before "<>" has been used will cause
	   @ARGV to be examined to determine if input is available.   Similarly, an "eof()" after
	   "<>" has returned end-of-file will assume you are processing another @ARGV list, and
	   if you haven't set @ARGV, will read input from "STDIN"; see "I/O Operators" in perlop.

	   In a "while (<>)" loop, "eof" or "eof(ARGV)" can be used to detect the end of each
	   file, whereas "eof()" will detect the end of the very last file only.  Examples:

	       # reset line numbering on each input file
	       while (<>) {
		   next if /^\s*#/;  # skip comments
		   print "$.\t$_";
	       } continue {
		   close ARGV if eof;  # Not eof()!
	       }

	       # insert dashes just before last line of last file
	       while (<>) {
		   if (eof()) {  # check for end of last file
		       print "--------------\n";
		   }
		   print;
		   last if eof();      # needed if we're reading from a terminal
	       }

	   Practical hint: you almost never need to use "eof" in Perl, because the input
	   operators typically return "undef" when they run out of data or encounter an error.

       eval EXPR
       eval BLOCK
       eval
	   In the first form, the return value of EXPR is parsed and executed as if it were a
	   little Perl program.  The value of the expression (which is itself determined within
	   scalar context) is first parsed, and if there were no errors, executed as a block
	   within the lexical context of the current Perl program.  This means, that in
	   particular, any outer lexical variables are visible to it, and any package variable
	   settings or subroutine and format definitions remain afterwards.

	   Note that the value is parsed every time the "eval" executes.  If EXPR is omitted,
	   evaluates $_.  This form is typically used to delay parsing and subsequent execution
	   of the text of EXPR until run time.

	   If the "unicode_eval" feature is enabled (which is the default under a "use 5.16" or
	   higher declaration), EXPR or $_ is treated as a string of characters, so "use utf8"
	   declarations have no effect, and source filters are forbidden.  In the absence of the
	   "unicode_eval" feature, the string will sometimes be treated as characters and
	   sometimes as bytes, depending on the internal encoding, and source filters activated
	   within the "eval" exhibit the erratic, but historical, behaviour of affecting some
	   outer file scope that is still compiling.  See also the "evalbytes" keyword, which
	   always treats its input as a byte stream and works properly with source filters, and
	   the feature pragma.

	   In the second form, the code within the BLOCK is parsed only once--at the same time
	   the code surrounding the "eval" itself was parsed--and executed within the context of
	   the current Perl program.  This form is typically used to trap exceptions more
	   efficiently than the first (see below), while also providing the benefit of checking
	   the code within BLOCK at compile time.

	   The final semicolon, if any, may be omitted from the value of EXPR or within the
	   BLOCK.

	   In both forms, the value returned is the value of the last expression evaluated inside
	   the mini-program; a return statement may be also used, just as with subroutines.  The
	   expression providing the return value is evaluated in void, scalar, or list context,
	   depending on the context of the "eval" itself.  See "wantarray" for more on how the
	   evaluation context can be determined.

	   If there is a syntax error or runtime error, or a "die" statement is executed, "eval"
	   returns "undef" in scalar context or an empty list in list context, and $@ is set to
	   the error message.  (Prior to 5.16, a bug caused "undef" to be returned in list
	   context for syntax errors, but not for runtime errors.)  If there was no error, $@ is
	   set to the empty string.  A control flow operator like "last" or "goto" can bypass the
	   setting of $@.  Beware that using "eval" neither silences Perl from printing warnings
	   to STDERR, nor does it stuff the text of warning messages into $@.  To do either of
	   those, you have to use the $SIG{__WARN__} facility, or turn off warnings inside the
	   BLOCK or EXPR using "no warnings 'all'".  See "warn", perlvar, warnings and
	   perllexwarn.

	   Note that, because "eval" traps otherwise-fatal errors, it is useful for determining
	   whether a particular feature (such as "socket" or "symlink") is implemented.  It is
	   also Perl's exception-trapping mechanism, where the die operator is used to raise
	   exceptions.

	   If you want to trap errors when loading an XS module, some problems with the binary
	   interface (such as Perl version skew) may be fatal even with "eval" unless
	   $ENV{PERL_DL_NONLAZY} is set.  See perlrun.

	   If the code to be executed doesn't vary, you may use the eval-BLOCK form to trap run-
	   time errors without incurring the penalty of recompiling each time.	The error, if
	   any, is still returned in $@.  Examples:

	       # make divide-by-zero nonfatal
	       eval { $answer = $a / $b; }; warn $@ if $@;

	       # same thing, but less efficient
	       eval '$answer = $a / $b'; warn $@ if $@;

	       # a compile-time error
	       eval { $answer = }; # WRONG

	       # a run-time error
	       eval '$answer =';   # sets $@

	   Using the "eval{}" form as an exception trap in libraries does have some issues.  Due
	   to the current arguably broken state of "__DIE__" hooks, you may wish not to trigger
	   any "__DIE__" hooks that user code may have installed.  You can use the "local
	   $SIG{__DIE__}" construct for this purpose, as this example shows:

	       # a private exception trap for divide-by-zero
	       eval { local $SIG{'__DIE__'}; $answer = $a / $b; };
	       warn $@ if $@;

	   This is especially significant, given that "__DIE__" hooks can call "die" again, which
	   has the effect of changing their error messages:

	       # __DIE__ hooks may modify error messages
	       {
		  local $SIG{'__DIE__'} =
			 sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x };
		  eval { die "foo lives here" };
		  print $@ if $@;		 # prints "bar lives here"
	       }

	   Because this promotes action at a distance, this counterintuitive behavior may be
	   fixed in a future release.

	   With an "eval", you should be especially careful to remember what's being looked at
	   when:

	       eval $x;        # CASE 1
	       eval "$x";      # CASE 2

	       eval '$x';      # CASE 3
	       eval { $x };    # CASE 4

	       eval "\$$x++";  # CASE 5
	       $$x++;	       # CASE 6

	   Cases 1 and 2 above behave identically: they run the code contained in the variable
	   $x.	(Although case 2 has misleading double quotes making the reader wonder what else
	   might be happening (nothing is).)  Cases 3 and 4 likewise behave in the same way: they
	   run the code '$x', which does nothing but return the value of $x.  (Case 4 is
	   preferred for purely visual reasons, but it also has the advantage of compiling at
	   compile-time instead of at run-time.)  Case 5 is a place where normally you would like
	   to use double quotes, except that in this particular situation, you can just use
	   symbolic references instead, as in case 6.

	   Before Perl 5.14, the assignment to $@ occurred before restoration of localized
	   variables, which means that for your code to run on older versions, a temporary is
	   required if you want to mask some but not all errors:

	       # alter $@ on nefarious repugnancy only
	       {
		  my $e;
		  {
		     local $@; # protect existing $@
		     eval { test_repugnancy() };
		     # $@ =~ /nefarious/ and die $@; # Perl 5.14 and higher only
		     $@ =~ /nefarious/ and $e = $@;
		  }
		  die $e if defined $e
	       }

	   "eval BLOCK" does not count as a loop, so the loop control statements "next", "last",
	   or "redo" cannot be used to leave or restart the block.

	   An "eval ''" executed within the "DB" package doesn't see the usual surrounding
	   lexical scope, but rather the scope of the first non-DB piece of code that called it.
	   You don't normally need to worry about this unless you are writing a Perl debugger.

       evalbytes EXPR
       evalbytes
	   This function is like "eval" with a string argument, except it always parses its
	   argument, or $_ if EXPR is omitted, as a string of bytes.  A string containing
	   characters whose ordinal value exceeds 255 results in an error.  Source filters
	   activated within the evaluated code apply to the code itself.

	   This function is only available under the "evalbytes" feature, a "use v5.16" (or
	   higher) declaration, or with a "CORE::" prefix.  See feature for more information.

       exec LIST
       exec PROGRAM LIST
	   The "exec" function executes a system command and never returns; use "system" instead
	   of "exec" if you want it to return.	It fails and returns false only if the command
	   does not exist and it is executed directly instead of via your system's command shell
	   (see below).

	   Since it's a common mistake to use "exec" instead of "system", Perl warns you if
	   "exec" is called in void context and if there is a following statement that isn't
	   "die", "warn", or "exit" (if "-w" is set--but you always do that, right?).  If you
	   really want to follow an "exec" with some other statement, you can use one of these
	   styles to avoid the warning:

	       exec ('foo')   or print STDERR "couldn't exec foo: $!";
	       { exec ('foo') }; print STDERR "couldn't exec foo: $!";

	   If there is more than one argument in LIST, or if LIST is an array with more than one
	   value, calls execvp(3) with the arguments in LIST.  If there is only one scalar
	   argument or an array with one element in it, the argument is checked for shell
	   metacharacters, and if there are any, the entire argument is passed to the system's
	   command shell for parsing (this is "/bin/sh -c" on Unix platforms, but varies on other
	   platforms).	If there are no shell metacharacters in the argument, it is split into
	   words and passed directly to "execvp", which is more efficient.  Examples:

	       exec '/bin/echo', 'Your arguments are: ', @ARGV;
	       exec "sort $outfile | uniq";

	   If you don't really want to execute the first argument, but want to lie to the program
	   you are executing about its own name, you can specify the program you actually want to
	   run as an "indirect object" (without a comma) in front of the LIST.	(This always
	   forces interpretation of the LIST as a multivalued list, even if there is only a
	   single scalar in the list.)	Example:

	       $shell = '/bin/csh';
	       exec $shell '-sh';    # pretend it's a login shell

	   or, more directly,

	       exec {'/bin/csh'} '-sh';  # pretend it's a login shell

	   When the arguments get executed via the system shell, results are subject to its
	   quirks and capabilities.  See "`STRING`" in perlop for details.

	   Using an indirect object with "exec" or "system" is also more secure.  This usage
	   (which also works fine with system()) forces interpretation of the arguments as a
	   multivalued list, even if the list had just one argument.  That way you're safe from
	   the shell expanding wildcards or splitting up words with whitespace in them.

	       @args = ( "echo surprise" );

	       exec @args;		 # subject to shell escapes
					   # if @args == 1
	       exec { $args[0] } @args;  # safe even with one-arg list

	   The first version, the one without the indirect object, ran the echo program, passing
	   it "surprise" an argument.  The second version didn't; it tried to run a program named
	   "echo surprise", didn't find it, and set $? to a non-zero value indicating failure.

	   Beginning with v5.6.0, Perl attempts to flush all files opened for output before the
	   exec, but this may not be supported on some platforms (see perlport).  To be safe, you
	   may need to set $| ($AUTOFLUSH in English) or call the "autoflush()" method of
	   "IO::Handle" on any open handles to avoid lost output.

	   Note that "exec" will not call your "END" blocks, nor will it invoke "DESTROY" methods
	   on your objects.

	   Portability issues: "exec" in perlport.

       exists EXPR
	   Given an expression that specifies an element of a hash, returns true if the specified
	   element in the hash has ever been initialized, even if the corresponding value is
	   undefined.

	       print "Exists\n"    if exists $hash{$key};
	       print "Defined\n"   if defined $hash{$key};
	       print "True\n"	   if $hash{$key};

	   exists may also be called on array elements, but its behavior is much less obvious and
	   is strongly tied to the use of "delete" on arrays.  Be aware that calling exists on
	   array values is deprecated and likely to be removed in a future version of Perl.

	       print "Exists\n"    if exists $array[$index];
	       print "Defined\n"   if defined $array[$index];
	       print "True\n"	   if $array[$index];

	   A hash or array element can be true only if it's defined and defined only if it
	   exists, but the reverse doesn't necessarily hold true.

	   Given an expression that specifies the name of a subroutine, returns true if the
	   specified subroutine has ever been declared, even if it is undefined.  Mentioning a
	   subroutine name for exists or defined does not count as declaring it.  Note that a
	   subroutine that does not exist may still be callable: its package may have an
	   "AUTOLOAD" method that makes it spring into existence the first time that it is
	   called; see perlsub.

	       print "Exists\n"  if exists &subroutine;
	       print "Defined\n" if defined &subroutine;

	   Note that the EXPR can be arbitrarily complicated as long as the final operation is a
	   hash or array key lookup or subroutine name:

	       if (exists $ref->{A}->{B}->{$key})  { }
	       if (exists $hash{A}{B}{$key})	   { }

	       if (exists $ref->{A}->{B}->[$ix])   { }
	       if (exists $hash{A}{B}[$ix])	   { }

	       if (exists &{$ref->{A}{B}{$key}})   { }

	   Although the most deeply nested array or hash element will not spring into existence
	   just because its existence was tested, any intervening ones will.  Thus "$ref->{"A"}"
	   and "$ref->{"A"}->{"B"}" will spring into existence due to the existence test for the
	   $key element above.	This happens anywhere the arrow operator is used, including even
	   here:

	       undef $ref;
	       if (exists $ref->{"Some key"})	 { }
	       print $ref;  # prints HASH(0x80d3d5c)

	   This surprising autovivification in what does not at first--or even second--glance
	   appear to be an lvalue context may be fixed in a future release.

	   Use of a subroutine call, rather than a subroutine name, as an argument to exists() is
	   an error.

	       exists &sub;    # OK
	       exists &sub();  # Error

       exit EXPR
       exit
	   Evaluates EXPR and exits immediately with that value.    Example:

	       $ans = <STDIN>;
	       exit 0 if $ans =~ /^[Xx]/;

	   See also "die".  If EXPR is omitted, exits with 0 status.  The only universally
	   recognized values for EXPR are 0 for success and 1 for error; other values are subject
	   to interpretation depending on the environment in which the Perl program is running.
	   For example, exiting 69 (EX_UNAVAILABLE) from a sendmail incoming-mail filter will
	   cause the mailer to return the item undelivered, but that's not true everywhere.

	   Don't use "exit" to abort a subroutine if there's any chance that someone might want
	   to trap whatever error happened.  Use "die" instead, which can be trapped by an
	   "eval".

	   The exit() function does not always exit immediately.  It calls any defined "END"
	   routines first, but these "END" routines may not themselves abort the exit.	Likewise
	   any object destructors that need to be called are called before the real exit.  "END"
	   routines and destructors can change the exit status by modifying $?.  If this is a
	   problem, you can call "POSIX::_exit($status)" to avoid END and destructor processing.
	   See perlmod for details.

	   Portability issues: "exit" in perlport.

       exp EXPR
       exp Returns e (the natural logarithm base) to the power of EXPR.  If EXPR is omitted,
	   gives "exp($_)".

       fc EXPR
       fc  Returns the casefolded version of EXPR.  This is the internal function implementing
	   the "\F" escape in double-quoted strings.

	   Casefolding is the process of mapping strings to a form where case differences are
	   erased; comparing two strings in their casefolded form is effectively a way of asking
	   if two strings are equal, regardless of case.

	   Roughly, if you ever found yourself writing this

	       lc($this) eq lc($that)  # Wrong!
		   # or
	       uc($this) eq uc($that)  # Also wrong!
		   # or
	       $this =~ /\Q$that/i     # Right!

	   Now you can write

	       fc($this) eq fc($that)

	   And get the correct results.

	   Perl only implements the full form of casefolding.  For further information on
	   casefolding, refer to the Unicode Standard, specifically sections 3.13 "Default Case
	   Operations", 4.2 "Case-Normative", and 5.18 "Case Mappings", available at
	   <http://www.unicode.org/versions/latest/>, as well as the Case Charts available at
	   <http://www.unicode.org/charts/case/>.

	   If EXPR is omitted, uses $_.

	   This function behaves the same way under various pragma, such as in a locale, as "lc"
	   does.

	   While the Unicode Standard defines two additional forms of casefolding, one for Turkic
	   languages and one that never maps one character into multiple characters, these are
	   not provided by the Perl core; However, the CPAN module "Unicode::Casing" may be used
	   to provide an implementation.

	   This keyword is available only when the "fc" feature is enabled, or when prefixed with
	   "CORE::"; See feature. Alternately, include a "use v5.16" or later to the current
	   scope.

       fcntl FILEHANDLE,FUNCTION,SCALAR
	   Implements the fcntl(2) function.  You'll probably have to say

	       use Fcntl;

	   first to get the correct constant definitions.  Argument processing and value returned
	   work just like "ioctl" below.  For example:

	       use Fcntl;
	       fcntl($filehandle, F_GETFL, $packed_return_buffer)
		   or die "can't fcntl F_GETFL: $!";

	   You don't have to check for "defined" on the return from "fcntl".  Like "ioctl", it
	   maps a 0 return from the system call into "0 but true" in Perl.  This string is true
	   in boolean context and 0 in numeric context.  It is also exempt from the normal -w
	   warnings on improper numeric conversions.

	   Note that "fcntl" raises an exception if used on a machine that doesn't implement
	   fcntl(2).  See the Fcntl module or your fcntl(2) manpage to learn what functions are
	   available on your system.

	   Here's an example of setting a filehandle named "REMOTE" to be non-blocking at the
	   system level.  You'll have to negotiate $| on your own, though.

	       use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);

	       $flags = fcntl(REMOTE, F_GETFL, 0)
			   or die "Can't get flags for the socket: $!\n";

	       $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
			   or die "Can't set flags for the socket: $!\n";

	   Portability issues: "fcntl" in perlport.

       __FILE__
	   A special token that returns the name of the file in which it occurs.

       fileno FILEHANDLE
	   Returns the file descriptor for a filehandle, or undefined if the filehandle is not
	   open.  If there is no real file descriptor at the OS level, as can happen with
	   filehandles connected to memory objects via "open" with a reference for the third
	   argument, -1 is returned.

	   This is mainly useful for constructing bitmaps for "select" and low-level POSIX tty-
	   handling operations.  If FILEHANDLE is an expression, the value is taken as an
	   indirect filehandle, generally its name.

	   You can use this to find out whether two handles refer to the same underlying
	   descriptor:

	       if (fileno(THIS) == fileno(THAT)) {
		   print "THIS and THAT are dups\n";
	       }

       flock FILEHANDLE,OPERATION
	   Calls flock(2), or an emulation of it, on FILEHANDLE.  Returns true for success, false
	   on failure.	Produces a fatal error if used on a machine that doesn't implement
	   flock(2), fcntl(2) locking, or lockf(3).  "flock" is Perl's portable file-locking
	   interface, although it locks entire files only, not records.

	   Two potentially non-obvious but traditional "flock" semantics are that it waits
	   indefinitely until the lock is granted, and that its locks are merely advisory.  Such
	   discretionary locks are more flexible, but offer fewer guarantees.  This means that
	   programs that do not also use "flock" may modify files locked with "flock".	See
	   perlport, your port's specific documentation, and your system-specific local manpages
	   for details.  It's best to assume traditional behavior if you're writing portable
	   programs.  (But if you're not, you should as always feel perfectly free to write for
	   your own system's idiosyncrasies (sometimes called "features").  Slavish adherence to
	   portability concerns shouldn't get in the way of your getting your job done.)

	   OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with LOCK_NB.
	   These constants are traditionally valued 1, 2, 8 and 4, but you can use the symbolic
	   names if you import them from the Fcntl module, either individually, or as a group
	   using the ":flock" tag.  LOCK_SH requests a shared lock, LOCK_EX requests an exclusive
	   lock, and LOCK_UN releases a previously requested lock.  If LOCK_NB is bitwise-or'ed
	   with LOCK_SH or LOCK_EX, then "flock" returns immediately rather than blocking waiting
	   for the lock; check the return status to see if you got it.

	   To avoid the possibility of miscoordination, Perl now flushes FILEHANDLE before
	   locking or unlocking it.

	   Note that the emulation built with lockf(3) doesn't provide shared locks, and it
	   requires that FILEHANDLE be open with write intent.	These are the semantics that
	   lockf(3) implements.  Most if not all systems implement lockf(3) in terms of fcntl(2)
	   locking, though, so the differing semantics shouldn't bite too many people.

	   Note that the fcntl(2) emulation of flock(3) requires that FILEHANDLE be open with
	   read intent to use LOCK_SH and requires that it be open with write intent to use
	   LOCK_EX.

	   Note also that some versions of "flock" cannot lock things over the network; you would
	   need to use the more system-specific "fcntl" for that.  If you like you can force Perl
	   to ignore your system's flock(2) function, and so provide its own fcntl(2)-based
	   emulation, by passing the switch "-Ud_flock" to the Configure program when you
	   configure and build a new Perl.

	   Here's a mailbox appender for BSD systems.

	       use Fcntl qw(:flock SEEK_END); # import LOCK_* and SEEK_END constants

	       sub lock {
		   my ($fh) = @_;
		   flock($fh, LOCK_EX) or die "Cannot lock mailbox - $!\n";

		   # and, in case someone appended while we were waiting...
		   seek($fh, 0, SEEK_END) or die "Cannot seek - $!\n";
	       }

	       sub unlock {
		   my ($fh) = @_;
		   flock($fh, LOCK_UN) or die "Cannot unlock mailbox - $!\n";
	       }

	       open(my $mbox, ">>", "/usr/spool/mail/$ENV{'USER'}")
		   or die "Can't open mailbox: $!";

	       lock($mbox);
	       print $mbox $msg,"\n\n";
	       unlock($mbox);

	   On systems that support a real flock(2), locks are inherited across fork() calls,
	   whereas those that must resort to the more capricious fcntl(2) function lose their
	   locks, making it seriously harder to write servers.

	   See also DB_File for other flock() examples.

	   Portability issues: "flock" in perlport.

       fork
	   Does a fork(2) system call to create a new process running the same program at the
	   same point.	It returns the child pid to the parent process, 0 to the child process,
	   or "undef" if the fork is unsuccessful.  File descriptors (and sometimes locks on
	   those descriptors) are shared, while everything else is copied.  On most systems
	   supporting fork(), great care has gone into making it extremely efficient (for
	   example, using copy-on-write technology on data pages), making it the dominant
	   paradigm for multitasking over the last few decades.

	   Beginning with v5.6.0, Perl attempts to flush all files opened for output before
	   forking the child process, but this may not be supported on some platforms (see
	   perlport).  To be safe, you may need to set $| ($AUTOFLUSH in English) or call the
	   "autoflush()" method of "IO::Handle" on any open handles to avoid duplicate output.

	   If you "fork" without ever waiting on your children, you will accumulate zombies.  On
	   some systems, you can avoid this by setting $SIG{CHLD} to "IGNORE".	See also perlipc
	   for more examples of forking and reaping moribund children.

	   Note that if your forked child inherits system file descriptors like STDIN and STDOUT
	   that are actually connected by a pipe or socket, even if you exit, then the remote
	   server (such as, say, a CGI script or a backgrounded job launched from a remote shell)
	   won't think you're done.  You should reopen those to /dev/null if it's any issue.

	   On some platforms such as Windows, where the fork() system call is not available, Perl
	   can be built to emulate fork() in the Perl interpreter.  The emulation is designed, at
	   the level of the Perl program, to be as compatible as possible with the "Unix" fork().
	   However it has limitations that have to be considered in code intended to be portable.
	   See perlfork for more details.

	   Portability issues: "fork" in perlport.

       format
	   Declare a picture format for use by the "write" function.  For example:

	       format Something =
		   Test: @<<<<<<<< @||||| @>>>>>
			 $str,	   $%,	  '$' . int($num)
	       .

	       $str = "widget";
	       $num = $cost/$quantity;
	       $~ = 'Something';
	       write;

	   See perlform for many details and examples.

       formline PICTURE,LIST
	   This is an internal function used by "format"s, though you may call it, too.  It
	   formats (see perlform) a list of values according to the contents of PICTURE, placing
	   the output into the format output accumulator, $^A (or $ACCUMULATOR in English).
	   Eventually, when a "write" is done, the contents of $^A are written to some
	   filehandle.	You could also read $^A and then set $^A back to "".  Note that a format
	   typically does one "formline" per line of form, but the "formline" function itself
	   doesn't care how many newlines are embedded in the PICTURE.	This means that the "~"
	   and "~~" tokens treat the entire PICTURE as a single line.  You may therefore need to
	   use multiple formlines to implement a single record format, just like the "format"
	   compiler.

	   Be careful if you put double quotes around the picture, because an "@" character may
	   be taken to mean the beginning of an array name.  "formline" always returns true.  See
	   perlform for other examples.

	   If you are trying to use this instead of "write" to capture the output, you may find
	   it easier to open a filehandle to a scalar ("open $fh, ">", \$output") and write to
	   that instead.

       getc FILEHANDLE
       getc
	   Returns the next character from the input file attached to FILEHANDLE, or the
	   undefined value at end of file or if there was an error (in the latter case $! is
	   set).  If FILEHANDLE is omitted, reads from STDIN.  This is not particularly
	   efficient.  However, it cannot be used by itself to fetch single characters without
	   waiting for the user to hit enter.  For that, try something more like:

	       if ($BSD_STYLE) {
		   system "stty cbreak </dev/tty >/dev/tty 2>&1";
	       }
	       else {
		   system "stty", '-icanon', 'eol', "\001";
	       }

	       $key = getc(STDIN);

	       if ($BSD_STYLE) {
		   system "stty -cbreak </dev/tty >/dev/tty 2>&1";
	       }
	       else {
		   system 'stty', 'icanon', 'eol', '^@'; # ASCII NUL
	       }
	       print "\n";

	   Determination of whether $BSD_STYLE should be set is left as an exercise to the
	   reader.

	   The "POSIX::getattr" function can do this more portably on systems purporting POSIX
	   compliance.	See also the "Term::ReadKey" module from your nearest CPAN site; details
	   on CPAN can be found under "CPAN" in perlmodlib.

       getlogin
	   This implements the C library function of the same name, which on most systems returns
	   the current login from /etc/utmp, if any.  If it returns the empty string, use
	   "getpwuid".

	       $login = getlogin || getpwuid($<) || "Kilroy";

	   Do not consider "getlogin" for authentication: it is not as secure as "getpwuid".

	   Portability issues: "getlogin" in perlport.

       getpeername SOCKET
	   Returns the packed sockaddr address of the other end of the SOCKET connection.

	       use Socket;
	       $hersockaddr    = getpeername(SOCK);
	       ($port, $iaddr) = sockaddr_in($hersockaddr);
	       $herhostname    = gethostbyaddr($iaddr, AF_INET);
	       $herstraddr     = inet_ntoa($iaddr);

       getpgrp PID
	   Returns the current process group for the specified PID.  Use a PID of 0 to get the
	   current process group for the current process.  Will raise an exception if used on a
	   machine that doesn't implement getpgrp(2).  If PID is omitted, returns the process
	   group of the current process.  Note that the POSIX version of "getpgrp" does not
	   accept a PID argument, so only "PID==0" is truly portable.

	   Portability issues: "getpgrp" in perlport.

       getppid
	   Returns the process id of the parent process.

	   Note for Linux users: Between v5.8.1 and v5.16.0 Perl would work around non-POSIX
	   thread semantics the minority of Linux systems (and Debian GNU/kFreeBSD systems) that
	   used LinuxThreads, this emulation has since been removed. See the documentation for $$
	   for details.

	   Portability issues: "getppid" in perlport.

       getpriority WHICH,WHO
	   Returns the current priority for a process, a process group, or a user.  (See
	   getpriority(2).)  Will raise a fatal exception if used on a machine that doesn't
	   implement getpriority(2).

	   Portability issues: "getpriority" in perlport.

       getpwnam NAME
       getgrnam NAME
       gethostbyname NAME
       getnetbyname NAME
       getprotobyname NAME
       getpwuid UID
       getgrgid GID
       getservbyname NAME,PROTO
       gethostbyaddr ADDR,ADDRTYPE
       getnetbyaddr ADDR,ADDRTYPE
       getprotobynumber NUMBER
       getservbyport PORT,PROTO
       getpwent
       getgrent
       gethostent
       getnetent
       getprotoent
       getservent
       setpwent
       setgrent
       sethostent STAYOPEN
       setnetent STAYOPEN
       setprotoent STAYOPEN
       setservent STAYOPEN
       endpwent
       endgrent
       endhostent
       endnetent
       endprotoent
       endservent
	   These routines are the same as their counterparts in the system C library.  In list
	   context, the return values from the various get routines are as follows:

	       ($name,$passwd,$uid,$gid,
		  $quota,$comment,$gcos,$dir,$shell,$expire) = getpw*
	       ($name,$passwd,$gid,$members) = getgr*
	       ($name,$aliases,$addrtype,$length,@addrs) = gethost*
	       ($name,$aliases,$addrtype,$net) = getnet*
	       ($name,$aliases,$proto) = getproto*
	       ($name,$aliases,$port,$proto) = getserv*

	   (If the entry doesn't exist you get an empty list.)

	   The exact meaning of the $gcos field varies but it usually contains the real name of
	   the user (as opposed to the login name) and other information pertaining to the user.
	   Beware, however, that in many system users are able to change this information and
	   therefore it cannot be trusted and therefore the $gcos is tainted (see perlsec).  The
	   $passwd and $shell, user's encrypted password and login shell, are also tainted, for
	   the same reason.

	   In scalar context, you get the name, unless the function was a lookup by name, in
	   which case you get the other thing, whatever it is.	(If the entry doesn't exist you
	   get the undefined value.)  For example:

	       $uid   = getpwnam($name);
	       $name  = getpwuid($num);
	       $name  = getpwent();
	       $gid   = getgrnam($name);
	       $name  = getgrgid($num);
	       $name  = getgrent();
	       #etc.

	   In getpw*() the fields $quota, $comment, and $expire are special in that they are
	   unsupported on many systems.  If the $quota is unsupported, it is an empty scalar.  If
	   it is supported, it usually encodes the disk quota.	If the $comment field is
	   unsupported, it is an empty scalar.	If it is supported it usually encodes some
	   administrative comment about the user.  In some systems the $quota field may be
	   $change or $age, fields that have to do with password aging.  In some systems the
	   $comment field may be $class.  The $expire field, if present, encodes the expiration
	   period of the account or the password.  For the availability and the exact meaning of
	   these fields in your system, please consult getpwnam(3) and your system's pwd.h file.
	   You can also find out from within Perl what your $quota and $comment fields mean and
	   whether you have the $expire field by using the "Config" module and the values
	   "d_pwquota", "d_pwage", "d_pwchange", "d_pwcomment", and "d_pwexpire".  Shadow
	   password files are supported only if your vendor has implemented them in the intuitive
	   fashion that calling the regular C library routines gets the shadow versions if you're
	   running under privilege or if there exists the shadow(3) functions as found in System
	   V (this includes Solaris and Linux).  Those systems that implement a proprietary
	   shadow password facility are unlikely to be supported.

	   The $members value returned by getgr*() is a space-separated list of the login names
	   of the members of the group.

	   For the gethost*() functions, if the "h_errno" variable is supported in C, it will be
	   returned to you via $? if the function call fails.  The @addrs value returned by a
	   successful call is a list of raw addresses returned by the corresponding library call.
	   In the Internet domain, each address is four bytes long; you can unpack it by saying
	   something like:

	       ($a,$b,$c,$d) = unpack('W4',$addr[0]);

	   The Socket library makes this slightly easier:

	       use Socket;
	       $iaddr = inet_aton("127.1"); # or whatever address
	       $name  = gethostbyaddr($iaddr, AF_INET);

	       # or going the other way
	       $straddr = inet_ntoa($iaddr);

	   In the opposite way, to resolve a hostname to the IP address you can write this:

	       use Socket;
	       $packed_ip = gethostbyname("www.perl.org");
	       if (defined $packed_ip) {
		   $ip_address = inet_ntoa($packed_ip);
	       }

	   Make sure "gethostbyname()" is called in SCALAR context and that its return value is
	   checked for definedness.

	   The "getprotobynumber" function, even though it only takes one argument, has the
	   precedence of a list operator, so beware:

	       getprotobynumber $number eq 'icmp'   # WRONG
	       getprotobynumber($number eq 'icmp')  # actually means this
	       getprotobynumber($number) eq 'icmp'  # better this way

	   If you get tired of remembering which element of the return list contains which return
	   value, by-name interfaces are provided in standard modules: "File::stat",
	   "Net::hostent", "Net::netent", "Net::protoent", "Net::servent", "Time::gmtime",
	   "Time::localtime", and "User::grent".  These override the normal built-ins, supplying
	   versions that return objects with the appropriate names for each field.  For example:

	      use File::stat;
	      use User::pwent;
	      $is_his = (stat($filename)->uid == pwent($whoever)->uid);

	   Even though it looks as though they're the same method calls (uid), they aren't,
	   because a "File::stat" object is different from a "User::pwent" object.

	   Portability issues: "getpwnam" in perlport to "endservent" in perlport.

       getsockname SOCKET
	   Returns the packed sockaddr address of this end of the SOCKET connection, in case you
	   don't know the address because you have several different IPs that the connection
	   might have come in on.

	       use Socket;
	       $mysockaddr = getsockname(SOCK);
	       ($port, $myaddr) = sockaddr_in($mysockaddr);
	       printf "Connect to %s [%s]\n",
		  scalar gethostbyaddr($myaddr, AF_INET),
		  inet_ntoa($myaddr);

       getsockopt SOCKET,LEVEL,OPTNAME
	   Queries the option named OPTNAME associated with SOCKET at a given LEVEL.  Options may
	   exist at multiple protocol levels depending on the socket type, but at least the
	   uppermost socket level SOL_SOCKET (defined in the "Socket" module) will exist.  To
	   query options at another level the protocol number of the appropriate protocol
	   controlling the option should be supplied.  For example, to indicate that an option is
	   to be interpreted by the TCP protocol, LEVEL should be set to the protocol number of
	   TCP, which you can get using "getprotobyname".

	   The function returns a packed string representing the requested socket option, or
	   "undef" on error, with the reason for the error placed in $!.  Just what is in the
	   packed string depends on LEVEL and OPTNAME; consult getsockopt(2) for details.  A
	   common case is that the option is an integer, in which case the result is a packed
	   integer, which you can decode using "unpack" with the "i" (or "I") format.

	   Here's an example to test whether Nagle's algorithm is enabled on a socket:

	       use Socket qw(:all);

	       defined(my $tcp = getprotobyname("tcp"))
		   or die "Could not determine the protocol number for tcp";
	       # my $tcp = IPPROTO_TCP; # Alternative
	       my $packed = getsockopt($socket, $tcp, TCP_NODELAY)
		   or die "getsockopt TCP_NODELAY: $!";
	       my $nodelay = unpack("I", $packed);
	       print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n";

	   Portability issues: "getsockopt" in perlport.

       glob EXPR
       glob
	   In list context, returns a (possibly empty) list of filename expansions on the value
	   of EXPR such as the standard Unix shell /bin/csh would do.  In scalar context, glob
	   iterates through such filename expansions, returning undef when the list is exhausted.
	   This is the internal function implementing the "<*.c>" operator, but you can use it
	   directly.  If EXPR is omitted, $_ is used.  The "<*.c>" operator is discussed in more
	   detail in "I/O Operators" in perlop.

	   Note that "glob" splits its arguments on whitespace and treats each segment as
	   separate pattern.  As such, "glob("*.c *.h")" matches all files with a .c or .h
	   extension.  The expression "glob(".* *")" matches all files in the current working
	   directory.  If you want to glob filenames that might contain whitespace, you'll have
	   to use extra quotes around the spacey filename to protect it.  For example, to glob
	   filenames that have an "e" followed by a space followed by an "f", use either of:

	       @spacies = <"*e f*">;
	       @spacies = glob '"*e f*"';
	       @spacies = glob q("*e f*");

	   If you had to get a variable through, you could do this:

	       @spacies = glob "'*${var}e f*'";
	       @spacies = glob qq("*${var}e f*");

	   If non-empty braces are the only wildcard characters used in the "glob", no filenames
	   are matched, but potentially many strings are returned.  For example, this produces
	   nine strings, one for each pairing of fruits and colors:

	       @many =	glob "{apple,tomato,cherry}={green,yellow,red}";

	   Beginning with v5.6.0, this operator is implemented using the standard "File::Glob"
	   extension.  See File::Glob for details, including "bsd_glob" which does not treat
	   whitespace as a pattern separator.

	   Portability issues: "glob" in perlport.

       gmtime EXPR
       gmtime
	   Works just like "localtime" but the returned values are localized for the standard
	   Greenwich time zone.

	   Note: When called in list context, $isdst, the last value returned by gmtime, is
	   always 0.  There is no Daylight Saving Time in GMT.

	   Portability issues: "gmtime" in perlport.

       goto LABEL
       goto EXPR
       goto &NAME
	   The "goto-LABEL" form finds the statement labeled with LABEL and resumes execution
	   there.  It can't be used to get out of a block or subroutine given to "sort".  It can
	   be used to go almost anywhere else within the dynamic scope, including out of
	   subroutines, but it's usually better to use some other construct such as "last" or
	   "die".  The author of Perl has never felt the need to use this form of "goto" (in
	   Perl, that is; C is another matter).  (The difference is that C does not offer named
	   loops combined with loop control.  Perl does, and this replaces most structured uses
	   of "goto" in other languages.)

	   The "goto-EXPR" form expects a label name, whose scope will be resolved dynamically.
	   This allows for computed "goto"s per FORTRAN, but isn't necessarily recommended if
	   you're optimizing for maintainability:

	       goto ("FOO", "BAR", "GLARCH")[$i];

	   As shown in this example, "goto-EXPR" is exempt from the "looks like a function" rule.
	   A pair of parentheses following it does not (necessarily) delimit its argument.
	   "goto("NE")."XT"" is equivalent to "goto NEXT".

	   Use of "goto-LABEL" or "goto-EXPR" to jump into a construct is deprecated and will
	   issue a warning.  Even then, it may not be used to go into any construct that requires
	   initialization, such as a subroutine or a "foreach" loop.  It also can't be used to go
	   into a construct that is optimized away.

	   The "goto-&NAME" form is quite different from the other forms of "goto".  In fact, it
	   isn't a goto in the normal sense at all, and doesn't have the stigma associated with
	   other gotos.  Instead, it exits the current subroutine (losing any changes set by
	   local()) and immediately calls in its place the named subroutine using the current
	   value of @_.  This is used by "AUTOLOAD" subroutines that wish to load another
	   subroutine and then pretend that the other subroutine had been called in the first
	   place (except that any modifications to @_ in the current subroutine are propagated to
	   the other subroutine.)  After the "goto", not even "caller" will be able to tell that
	   this routine was called first.

	   NAME needn't be the name of a subroutine; it can be a scalar variable containing a
	   code reference or a block that evaluates to a code reference.

       grep BLOCK LIST
       grep EXPR,LIST
	   This is similar in spirit to, but not the same as, grep(1) and its relatives.  In
	   particular, it is not limited to using regular expressions.

	   Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each
	   element) and returns the list value consisting of those elements for which the
	   expression evaluated to true.  In scalar context, returns the number of times the
	   expression was true.

	       @foo = grep(!/^#/, @bar);    # weed out comments

	   or equivalently,

	       @foo = grep {!/^#/} @bar;    # weed out comments

	   Note that $_ is an alias to the list value, so it can be used to modify the elements
	   of the LIST.  While this is useful and supported, it can cause bizarre results if the
	   elements of LIST are not variables.	Similarly, grep returns aliases into the original
	   list, much as a for loop's index variable aliases the list elements.  That is,
	   modifying an element of a list returned by grep (for example, in a "foreach", "map" or
	   another "grep") actually modifies the element in the original list.	This is usually
	   something to be avoided when writing clear code.

	   If $_ is lexical in the scope where the "grep" appears (because it has been declared
	   with "my $_") then, in addition to being locally aliased to the list elements, $_
	   keeps being lexical inside the block; i.e., it can't be seen from the outside,
	   avoiding any potential side-effects.

	   See also "map" for a list composed of the results of the BLOCK or EXPR.

       hex EXPR
       hex Interprets EXPR as a hex string and returns the corresponding value.  (To convert
	   strings that might start with either 0, "0x", or "0b", see "oct".)  If EXPR is
	   omitted, uses $_.

	       print hex '0xAf'; # prints '175'
	       print hex 'aF';	 # same

	   Hex strings may only represent integers.  Strings that would cause integer overflow
	   trigger a warning.  Leading whitespace is not stripped, unlike oct().  To present
	   something as hex, look into "printf", "sprintf", and "unpack".

       import LIST
	   There is no builtin "import" function.  It is just an ordinary method (subroutine)
	   defined (or inherited) by modules that wish to export names to another module.  The
	   "use" function calls the "import" method for the package used.  See also "use",
	   perlmod, and Exporter.

       index STR,SUBSTR,POSITION
       index STR,SUBSTR
	   The index function searches for one string within another, but without the wildcard-
	   like behavior of a full regular-expression pattern match.  It returns the position of
	   the first occurrence of SUBSTR in STR at or after POSITION.	If POSITION is omitted,
	   starts searching from the beginning of the string.  POSITION before the beginning of
	   the string or after its end is treated as if it were the beginning or the end,
	   respectively.  POSITION and the return value are based at zero.  If the substring is
	   not found, "index" returns -1.

       int EXPR
       int Returns the integer portion of EXPR.  If EXPR is omitted, uses $_.  You should not use
	   this function for rounding: one because it truncates towards 0, and two because
	   machine representations of floating-point numbers can sometimes produce
	   counterintuitive results.  For example, "int(-6.725/0.025)" produces -268 rather than
	   the correct -269; that's because it's really more like -268.99999999999994315658
	   instead.  Usually, the "sprintf", "printf", or the "POSIX::floor" and "POSIX::ceil"
	   functions will serve you better than will int().

       ioctl FILEHANDLE,FUNCTION,SCALAR
	   Implements the ioctl(2) function.  You'll probably first have to say

	       require "sys/ioctl.ph";	# probably in $Config{archlib}/sys/ioctl.ph

	   to get the correct function definitions.  If sys/ioctl.ph doesn't exist or doesn't
	   have the correct definitions you'll have to roll your own, based on your C header
	   files such as <sys/ioctl.h>.  (There is a Perl script called h2ph that comes with the
	   Perl kit that may help you in this, but it's nontrivial.)  SCALAR will be read and/or
	   written depending on the FUNCTION; a C pointer to the string value of SCALAR will be
	   passed as the third argument of the actual "ioctl" call.  (If SCALAR has no string
	   value but does have a numeric value, that value will be passed rather than a pointer
	   to the string value.  To guarantee this to be true, add a 0 to the scalar before using
	   it.)  The "pack" and "unpack" functions may be needed to manipulate the values of
	   structures used by "ioctl".

	   The return value of "ioctl" (and "fcntl") is as follows:

	       if OS returns:	   then Perl returns:
		   -1		    undefined value
		    0		   string "0 but true"
	       anything else	       that number

	   Thus Perl returns true on success and false on failure, yet you can still easily
	   determine the actual value returned by the operating system:

	       $retval = ioctl(...) || -1;
	       printf "System returned %d\n", $retval;

	   The special string "0 but true" is exempt from -w complaints about improper numeric
	   conversions.

	   Portability issues: "ioctl" in perlport.

       join EXPR,LIST
	   Joins the separate strings of LIST into a single string with fields separated by the
	   value of EXPR, and returns that new string.	Example:

	       $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);

	   Beware that unlike "split", "join" doesn't take a pattern as its first argument.
	   Compare "split".

       keys HASH
       keys ARRAY
       keys EXPR
	   Called in list context, returns a list consisting of all the keys of the named hash,
	   or in Perl 5.12 or later only, the indices of an array.  Perl releases prior to 5.12
	   will produce a syntax error if you try to use an array argument.  In scalar context,
	   returns the number of keys or indices.

	   The keys of a hash are returned in an apparently random order.  The actual random
	   order is subject to change in future versions of Perl, but it is guaranteed to be the
	   same order as either the "values" or "each" function produces (given that the hash has
	   not been modified).	Since Perl 5.8.1 the ordering can be different even between
	   different runs of Perl for security reasons (see "Algorithmic Complexity Attacks" in
	   perlsec).

	   As a side effect, calling keys() resets the internal interator of the HASH or ARRAY
	   (see "each").  In particular, calling keys() in void context resets the iterator with
	   no other overhead.

	   Here is yet another way to print your environment:

	       @keys = keys %ENV;
	       @values = values %ENV;
	       while (@keys) {
		   print pop(@keys), '=', pop(@values), "\n";
	       }

	   or how about sorted by key:

	       foreach $key (sort(keys %ENV)) {
		   print $key, '=', $ENV{$key}, "\n";
	       }

	   The returned values are copies of the original keys in the hash, so modifying them
	   will not affect the original hash.  Compare "values".

	   To sort a hash by value, you'll need to use a "sort" function.  Here's a descending
	   numeric sort of a hash by its values:

	       foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
		   printf "%4d %s\n", $hash{$key}, $key;
	       }

	   Used as an lvalue, "keys" allows you to increase the number of hash buckets allocated
	   for the given hash.	This can gain you a measure of efficiency if you know the hash is
	   going to get big.  (This is similar to pre-extending an array by assigning a larger
	   number to $#array.)	If you say

	       keys %hash = 200;

	   then %hash will have at least 200 buckets allocated for it--256 of them, in fact,
	   since it rounds up to the next power of two.  These buckets will be retained even if
	   you do "%hash = ()", use "undef %hash" if you want to free the storage while %hash is
	   still in scope.  You can't shrink the number of buckets allocated for the hash using
	   "keys" in this way (but you needn't worry about doing this by accident, as trying has
	   no effect).	"keys @array" in an lvalue context is a syntax error.

	   Starting with Perl 5.14, "keys" can take a scalar EXPR, which must contain a reference
	   to an unblessed hash or array.  The argument will be dereferenced automatically.  This
	   aspect of "keys" is considered highly experimental.	The exact behaviour may change in
	   a future version of Perl.

	       for (keys $hashref) { ... }
	       for (keys $obj->get_arrayref) { ... }

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.012;  # so keys/values/each work on arrays
	       use 5.014;  # so keys/values/each work on scalars (experimental)

	   See also "each", "values", and "sort".

       kill SIGNAL, LIST
       kill SIGNAL
	   Sends a signal to a list of processes.  Returns the number of processes successfully
	   signaled (which is not necessarily the same as the number actually killed).

	       $cnt = kill 1, $child1, $child2;
	       kill 9, @goners;

	   If SIGNAL is zero, no signal is sent to the process, but "kill" checks whether it's
	   possible to send a signal to it (that means, to be brief, that the process is owned by
	   the same user, or we are the super-user).  This is useful to check that a child
	   process is still alive (even if only as a zombie) and hasn't changed its UID.  See
	   perlport for notes on the portability of this construct.

	   Unlike in the shell, if SIGNAL is negative, it kills process groups instead of
	   processes.  That means you usually want to use positive not negative signals.  You may
	   also use a signal name in quotes.

	   The behavior of kill when a PROCESS number is zero or negative depends on the
	   operating system.  For example, on POSIX-conforming systems, zero will signal the
	   current process group and -1 will signal all processes.

	   See "Signals" in perlipc for more details.

	   On some platforms such as Windows where the fork() system call is not available.  Perl
	   can be built to emulate fork() at the interpreter level.  This emulation has
	   limitations related to kill that have to be considered, for code running on Windows
	   and in code intended to be portable.

	   See perlfork for more details.

	   If there is no LIST of processes, no signal is sent, and the return value is 0.  This
	   form is sometimes used, however, because it causes tainting checks to be run.  But see
	   "Laundering and Detecting Tainted Data" in perlsec.

	   Portability issues: "kill" in perlport.

       last LABEL
       last
	   The "last" command is like the "break" statement in C (as used in loops); it
	   immediately exits the loop in question.  If the LABEL is omitted, the command refers
	   to the innermost enclosing loop.  The "continue" block, if any, is not executed:

	       LINE: while (<STDIN>) {
		   last LINE if /^$/;  # exit when done with header
		   #...
	       }

	   "last" cannot be used to exit a block that returns a value such as "eval {}", "sub
	   {}", or "do {}", and should not be used to exit a grep() or map() operation.

	   Note that a block by itself is semantically identical to a loop that executes once.
	   Thus "last" can be used to effect an early exit out of such a block.

	   See also "continue" for an illustration of how "last", "next", and "redo" work.

       lc EXPR
       lc  Returns a lowercased version of EXPR.  This is the internal function implementing the
	   "\L" escape in double-quoted strings.

	   If EXPR is omitted, uses $_.

	   What gets returned depends on several factors:

	   If "use bytes" is in effect:
	       On EBCDIC platforms
		   The results are what the C language system call "tolower()" returns.

	       On ASCII platforms
		   The results follow ASCII semantics.	Only characters "A-Z" change, to "a-z"
		   respectively.

	   Otherwise, if "use locale" (but not "use locale ':not_characters'") is in effect:
	       Respects current LC_CTYPE locale for code points < 256; and uses Unicode semantics
	       for the remaining code points (this last can only happen if the UTF8 flag is also
	       set).  See perllocale.

	       A deficiency in this is that case changes that cross the 255/256 boundary are not
	       well-defined.  For example, the lower case of LATIN CAPITAL LETTER SHARP S
	       (U+1E9E) in Unicode semantics is U+00DF (on ASCII platforms).   But under "use
	       locale", the lower case of U+1E9E is itself, because 0xDF may not be LATIN SMALL
	       LETTER SHARP S in the current locale, and Perl has no way of knowing if that
	       character even exists in the locale, much less what code point it is.  Perl
	       returns the input character unchanged, for all instances (and there aren't many)
	       where the 255/256 boundary would otherwise be crossed.

	   Otherwise, If EXPR has the UTF8 flag set:
	       Unicode semantics are used for the case change.

	   Otherwise, if "use feature 'unicode_strings'" or "use locale ':not_characters'") is in
	   effect:
	       Unicode semantics are used for the case change.

	   Otherwise:
	       On EBCDIC platforms
		   The results are what the C language system call "tolower()" returns.

	       On ASCII platforms
		   ASCII semantics are used for the case change.  The lowercase of any character
		   outside the ASCII range is the character itself.

       lcfirst EXPR
       lcfirst
	   Returns the value of EXPR with the first character lowercased.  This is the internal
	   function implementing the "\l" escape in double-quoted strings.

	   If EXPR is omitted, uses $_.

	   This function behaves the same way under various pragmata, such as in a locale, as
	   "lc" does.

       length EXPR
       length
	   Returns the length in characters of the value of EXPR.  If EXPR is omitted, returns
	   the length of $_.  If EXPR is undefined, returns "undef".

	   This function cannot be used on an entire array or hash to find out how many elements
	   these have.	For that, use "scalar @array" and "scalar keys %hash", respectively.

	   Like all Perl character operations, length() normally deals in logical characters, not
	   physical bytes.  For how many bytes a string encoded as UTF-8 would take up, use
	   "length(Encode::encode_utf8(EXPR))" (you'll have to "use Encode" first).  See Encode
	   and perlunicode.

       __LINE__
	   A special token that compiles to the current line number.

       link OLDFILE,NEWFILE
	   Creates a new filename linked to the old filename.  Returns true for success, false
	   otherwise.

	   Portability issues: "link" in perlport.

       listen SOCKET,QUEUESIZE
	   Does the same thing that the listen(2) system call does.  Returns true if it
	   succeeded, false otherwise.	See the example in "Sockets: Client/Server Communication"
	   in perlipc.

       local EXPR
	   You really probably want to be using "my" instead, because "local" isn't what most
	   people think of as "local".	See "Private Variables via my()" in perlsub for details.

	   A local modifies the listed variables to be local to the enclosing block, file, or
	   eval.  If more than one value is listed, the list must be placed in parentheses.  See
	   "Temporary Values via local()" in perlsub for details, including issues with tied
	   arrays and hashes.

	   The "delete local EXPR" construct can also be used to localize the deletion of
	   array/hash elements to the current block.  See "Localized deletion of elements of
	   composite types" in perlsub.

       localtime EXPR
       localtime
	   Converts a time as returned by the time function to a 9-element list with the time
	   analyzed for the local time zone.  Typically used as follows:

	       #  0    1    2	  3	4    5	   6	 7     8
	       ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
							   localtime(time);

	   All list elements are numeric and come straight out of the C `struct tm'.  $sec, $min,
	   and $hour are the seconds, minutes, and hours of the specified time.

	   $mday is the day of the month and $mon the month in the range 0..11, with 0 indicating
	   January and 11 indicating December.	This makes it easy to get a month name from a
	   list:

	       my @abbr = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
	       print "$abbr[$mon] $mday";
	       # $mon=9, $mday=18 gives "Oct 18"

	   $year contains the number of years since 1900.  To get a 4-digit year write:

	       $year += 1900;

	   To get the last two digits of the year (e.g., "01" in 2001) do:

	       $year = sprintf("%02d", $year % 100);

	   $wday is the day of the week, with 0 indicating Sunday and 3 indicating Wednesday.
	   $yday is the day of the year, in the range 0..364 (or 0..365 in leap years.)

	   $isdst is true if the specified time occurs during Daylight Saving Time, false
	   otherwise.

	   If EXPR is omitted, "localtime()" uses the current time (as returned by time(3)).

	   In scalar context, "localtime()" returns the ctime(3) value:

	       $now_string = localtime;  # e.g., "Thu Oct 13 04:54:34 1994"

	   The format of this scalar value is not locale-dependent but built into Perl.  For GMT
	   instead of local time use the "gmtime" builtin.  See also the "Time::Local" module
	   (for converting seconds, minutes, hours, and such back to the integer value returned
	   by time()), and the POSIX module's strftime(3) and mktime(3) functions.

	   To get somewhat similar but locale-dependent date strings, set up your locale
	   environment variables appropriately (please see perllocale) and try for example:

	       use POSIX qw(strftime);
	       $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;
	       # or for GMT formatted appropriately for your locale:
	       $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;

	   Note that the %a and %b, the short forms of the day of the week and the month of the
	   year, may not necessarily be three characters wide.

	   The Time::gmtime and Time::localtime modules provide a convenient, by-name access
	   mechanism to the gmtime() and localtime() functions, respectively.

	   For a comprehensive date and time representation look at the DateTime module on CPAN.

	   Portability issues: "localtime" in perlport.

       lock THING
	   This function places an advisory lock on a shared variable or referenced object
	   contained in THING until the lock goes out of scope.

	   The value returned is the scalar itself, if the argument is a scalar, or a reference,
	   if the argument is a hash, array or subroutine.

	   lock() is a "weak keyword" : this means that if you've defined a function by this name
	   (before any calls to it), that function will be called instead.  If you are not under
	   "use threads::shared" this does nothing.  See threads::shared.

       log EXPR
       log Returns the natural logarithm (base e) of EXPR.  If EXPR is omitted, returns the log
	   of $_.  To get the log of another base, use basic algebra: The base-N log of a number
	   is equal to the natural log of that number divided by the natural log of N.	For
	   example:

	       sub log10 {
		   my $n = shift;
		   return log($n)/log(10);
	       }

	   See also "exp" for the inverse operation.

       lstat FILEHANDLE
       lstat EXPR
       lstat DIRHANDLE
       lstat
	   Does the same thing as the "stat" function (including setting the special "_"
	   filehandle) but stats a symbolic link instead of the file the symbolic link points to.
	   If symbolic links are unimplemented on your system, a normal "stat" is done.  For much
	   more detailed information, please see the documentation for "stat".

	   If EXPR is omitted, stats $_.

	   Portability issues: "lstat" in perlport.

       m// The match operator.	See "Regexp Quote-Like Operators" in perlop.

       map BLOCK LIST
       map EXPR,LIST
	   Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each
	   element) and returns the list value composed of the results of each such evaluation.
	   In scalar context, returns the total number of elements so generated.  Evaluates BLOCK
	   or EXPR in list context, so each element of LIST may produce zero, one, or more
	   elements in the returned value.

	       @chars = map(chr, @numbers);

	   translates a list of numbers to the corresponding characters.

	       my @squares = map { $_ * $_ } @numbers;

	   translates a list of numbers to their squared values.

	       my @squares = map { $_ > 5 ? ($_ * $_) : () } @numbers;

	   shows that number of returned elements can differ from the number of input elements.
	   To omit an element, return an empty list ().  This could also be achieved by writing

	       my @squares = map { $_ * $_ } grep { $_ > 5 } @numbers;

	   which makes the intention more clear.

	   Map always returns a list, which can be assigned to a hash such that the elements
	   become key/value pairs.  See perldata for more details.

	       %hash = map { get_a_key_for($_) => $_ } @array;

	   is just a funny way to write

	       %hash = ();
	       foreach (@array) {
		   $hash{get_a_key_for($_)} = $_;
	       }

	   Note that $_ is an alias to the list value, so it can be used to modify the elements
	   of the LIST.  While this is useful and supported, it can cause bizarre results if the
	   elements of LIST are not variables.	Using a regular "foreach" loop for this purpose
	   would be clearer in most cases.  See also "grep" for an array composed of those items
	   of the original list for which the BLOCK or EXPR evaluates to true.

	   If $_ is lexical in the scope where the "map" appears (because it has been declared
	   with "my $_"), then, in addition to being locally aliased to the list elements, $_
	   keeps being lexical inside the block; that is, it can't be seen from the outside,
	   avoiding any potential side-effects.

	   "{" starts both hash references and blocks, so "map { ..." could be either the start
	   of map BLOCK LIST or map EXPR, LIST.  Because Perl doesn't look ahead for the closing
	   "}" it has to take a guess at which it's dealing with based on what it finds just
	   after the "{".  Usually it gets it right, but if it doesn't it won't realize something
	   is wrong until it gets to the "}" and encounters the missing (or unexpected) comma.
	   The syntax error will be reported close to the "}", but you'll need to change
	   something near the "{" such as using a unary "+" to give Perl some help:

	       %hash = map {  "\L$_" => 1  } @array  # perl guesses EXPR.  wrong
	       %hash = map { +"\L$_" => 1  } @array  # perl guesses BLOCK. right
	       %hash = map { ("\L$_" => 1) } @array  # this also works
	       %hash = map {  lc($_) => 1  } @array  # as does this.
	       %hash = map +( lc($_) => 1 ), @array  # this is EXPR and works!

	       %hash = map  ( lc($_), 1 ),   @array  # evaluates to (1, @array)

	   or to force an anon hash constructor use "+{":

	      @hashes = map +{ lc($_) => 1 }, @array # EXPR, so needs comma at end

	   to get a list of anonymous hashes each with only one entry apiece.

       mkdir FILENAME,MASK
       mkdir FILENAME
       mkdir
	   Creates the directory specified by FILENAME, with permissions specified by MASK (as
	   modified by "umask").  If it succeeds it returns true; otherwise it returns false and
	   sets $! (errno).  MASK defaults to 0777 if omitted, and FILENAME defaults to $_ if
	   omitted.

	   In general, it is better to create directories with a permissive MASK and let the user
	   modify that with their "umask" than it is to supply a restrictive MASK and give the
	   user no way to be more permissive.  The exceptions to this rule are when the file or
	   directory should be kept private (mail files, for instance).  The perlfunc(1) entry on
	   "umask" discusses the choice of MASK in more detail.

	   Note that according to the POSIX 1003.1-1996 the FILENAME may have any number of
	   trailing slashes.  Some operating and filesystems do not get this right, so Perl
	   automatically removes all trailing slashes to keep everyone happy.

	   To recursively create a directory structure, look at the "mkpath" function of the
	   File::Path module.

       msgctl ID,CMD,ARG
	   Calls the System V IPC function msgctl(2).  You'll probably have to say

	       use IPC::SysV;

	   first to get the correct constant definitions.  If CMD is "IPC_STAT", then ARG must be
	   a variable that will hold the returned "msqid_ds" structure.  Returns like "ioctl":
	   the undefined value for error, "0 but true" for zero, or the actual return value
	   otherwise.  See also "SysV IPC" in perlipc and the documentation for "IPC::SysV" and
	   "IPC::Semaphore".

	   Portability issues: "msgctl" in perlport.

       msgget KEY,FLAGS
	   Calls the System V IPC function msgget(2).  Returns the message queue id, or "undef"
	   on error.  See also "SysV IPC" in perlipc and the documentation for "IPC::SysV" and
	   "IPC::Msg".

	   Portability issues: "msgget" in perlport.

       msgrcv ID,VAR,SIZE,TYPE,FLAGS
	   Calls the System V IPC function msgrcv to receive a message from message queue ID into
	   variable VAR with a maximum message size of SIZE.  Note that when a message is
	   received, the message type as a native long integer will be the first thing in VAR,
	   followed by the actual message.  This packing may be opened with "unpack("l! a*")".
	   Taints the variable.  Returns true if successful, false on error.  See also "SysV IPC"
	   in perlipc and the documentation for "IPC::SysV" and "IPC::SysV::Msg".

	   Portability issues: "msgrcv" in perlport.

       msgsnd ID,MSG,FLAGS
	   Calls the System V IPC function msgsnd to send the message MSG to the message queue
	   ID.	MSG must begin with the native long integer message type, be followed by the
	   length of the actual message, and then finally the message itself.  This kind of
	   packing can be achieved with "pack("l! a*", $type, $message)".  Returns true if
	   successful, false on error.	See also the "IPC::SysV" and "IPC::SysV::Msg"
	   documentation.

	   Portability issues: "msgsnd" in perlport.

       my EXPR
       my TYPE EXPR
       my EXPR : ATTRS
       my TYPE EXPR : ATTRS
	   A "my" declares the listed variables to be local (lexically) to the enclosing block,
	   file, or "eval".  If more than one value is listed, the list must be placed in
	   parentheses.

	   The exact semantics and interface of TYPE and ATTRS are still evolving.  TYPE is
	   currently bound to the use of the "fields" pragma, and attributes are handled using
	   the "attributes" pragma, or starting from Perl 5.8.0 also via the
	   "Attribute::Handlers" module.  See "Private Variables via my()" in perlsub for
	   details, and fields, attributes, and Attribute::Handlers.

       next LABEL
       next
	   The "next" command is like the "continue" statement in C; it starts the next iteration
	   of the loop:

	       LINE: while (<STDIN>) {
		   next LINE if /^#/;  # discard comments
		   #...
	       }

	   Note that if there were a "continue" block on the above, it would get executed even on
	   discarded lines.  If LABEL is omitted, the command refers to the innermost enclosing
	   loop.

	   "next" cannot be used to exit a block which returns a value such as "eval {}", "sub
	   {}", or "do {}", and should not be used to exit a grep() or map() operation.

	   Note that a block by itself is semantically identical to a loop that executes once.
	   Thus "next" will exit such a block early.

	   See also "continue" for an illustration of how "last", "next", and "redo" work.

       no MODULE VERSION LIST
       no MODULE VERSION
       no MODULE LIST
       no MODULE
       no VERSION
	   See the "use" function, of which "no" is the opposite.

       oct EXPR
       oct Interprets EXPR as an octal string and returns the corresponding value.  (If EXPR
	   happens to start off with "0x", interprets it as a hex string.  If EXPR starts off
	   with "0b", it is interpreted as a binary string.  Leading whitespace is ignored in all
	   three cases.)  The following will handle decimal, binary, octal, and hex in standard
	   Perl notation:

	       $val = oct($val) if $val =~ /^0/;

	   If EXPR is omitted, uses $_.   To go the other way (produce a number in octal), use
	   sprintf() or printf():

	       $dec_perms = (stat("filename"))[2] & 07777;
	       $oct_perm_str = sprintf "%o", $perms;

	   The oct() function is commonly used when a string such as 644 needs to be converted
	   into a file mode, for example.  Although Perl automatically converts strings into
	   numbers as needed, this automatic conversion assumes base 10.

	   Leading white space is ignored without warning, as too are any trailing non-digits,
	   such as a decimal point ("oct" only handles non-negative integers, not negative
	   integers or floating point).

       open FILEHANDLE,EXPR
       open FILEHANDLE,MODE,EXPR
       open FILEHANDLE,MODE,EXPR,LIST
       open FILEHANDLE,MODE,REFERENCE
       open FILEHANDLE
	   Opens the file whose filename is given by EXPR, and associates it with FILEHANDLE.

	   Simple examples to open a file for reading:

	       open(my $fh, "<", "input.txt")
		   or die "cannot open < input.txt: $!";

	   and for writing:

	       open(my $fh, ">", "output.txt")
		   or die "cannot open > output.txt: $!";

	   (The following is a comprehensive reference to open(): for a gentler introduction you
	   may consider perlopentut.)

	   If FILEHANDLE is an undefined scalar variable (or array or hash element), a new
	   filehandle is autovivified, meaning that the variable is assigned a reference to a
	   newly allocated anonymous filehandle.  Otherwise if FILEHANDLE is an expression, its
	   value is the real filehandle.  (This is considered a symbolic reference, so "use
	   strict "refs"" should not be in effect.)

	   If EXPR is omitted, the global (package) scalar variable of the same name as the
	   FILEHANDLE contains the filename.  (Note that lexical variables--those declared with
	   "my" or "state"--will not work for this purpose; so if you're using "my" or "state",
	   specify EXPR in your call to open.)

	   If three (or more) arguments are specified, the open mode (including optional
	   encoding) in the second argument are distinct from the filename in the third.  If MODE
	   is "<" or nothing, the file is opened for input.  If MODE is ">", the file is opened
	   for output, with existing files first being truncated ("clobbered") and nonexisting
	   files newly created.  If MODE is ">>", the file is opened for appending, again being
	   created if necessary.

	   You can put a "+" in front of the ">" or "<" to indicate that you want both read and
	   write access to the file; thus "+<" is almost always preferred for read/write
	   updates--the "+>" mode would clobber the file first.  You can't usually use either
	   read-write mode for updating textfiles, since they have variable-length records.  See
	   the -i switch in perlrun for a better approach.  The file is created with permissions
	   of 0666 modified by the process's "umask" value.

	   These various prefixes correspond to the fopen(3) modes of "r", "r+", "w", "w+", "a",
	   and "a+".

	   In the one- and two-argument forms of the call, the mode and filename should be
	   concatenated (in that order), preferably separated by white space.  You can--but
	   shouldn't--omit the mode in these forms when that mode is "<".  It is always safe to
	   use the two-argument form of "open" if the filename argument is a known literal.

	   For three or more arguments if MODE is "|-", the filename is interpreted as a command
	   to which output is to be piped, and if MODE is "-|", the filename is interpreted as a
	   command that pipes output to us.  In the two-argument (and one-argument) form, one
	   should replace dash ("-") with the command.	See "Using open() for IPC" in perlipc for
	   more examples of this.  (You are not allowed to "open" to a command that pipes both in
	   and out, but see IPC::Open2, IPC::Open3, and "Bidirectional Communication with Another
	   Process" in perlipc for alternatives.)

	   In the form of pipe opens taking three or more arguments, if LIST is specified (extra
	   arguments after the command name) then LIST becomes arguments to the command invoked
	   if the platform supports it.  The meaning of "open" with more than three arguments for
	   non-pipe modes is not yet defined, but experimental "layers" may give extra LIST
	   arguments meaning.

	   In the two-argument (and one-argument) form, opening "<-" or "-" opens STDIN and
	   opening ">-" opens STDOUT.

	   You may (and usually should) use the three-argument form of open to specify I/O layers
	   (sometimes referred to as "disciplines") to apply to the handle that affect how the
	   input and output are processed (see open and PerlIO for more details).  For example:

	     open(my $fh, "<:encoding(UTF-8)", "filename")
	       || die "can't open UTF-8 encoded filename: $!";

	   opens the UTF8-encoded file containing Unicode characters; see perluniintro.  Note
	   that if layers are specified in the three-argument form, then default layers stored in
	   ${^OPEN} (see perlvar; usually set by the open pragma or the switch -CioD) are
	   ignored.  Those layers will also be ignored if you specifying a colon with no name
	   following it.  In that case the default layer for the operating system (:raw on Unix,
	   :crlf on Windows) is used.

	   Open returns nonzero on success, the undefined value otherwise.  If the "open"
	   involved a pipe, the return value happens to be the pid of the subprocess.

	   If you're running Perl on a system that distinguishes between text files and binary
	   files, then you should check out "binmode" for tips for dealing with this.  The key
	   distinction between systems that need "binmode" and those that don't is their text
	   file formats.  Systems like Unix, Mac OS, and Plan 9, that end lines with a single
	   character and encode that character in C as "\n" do not need "binmode".  The rest need
	   it.

	   When opening a file, it's seldom a good idea to continue if the request failed, so
	   "open" is frequently used with "die".  Even if "die" won't do what you want (say, in a
	   CGI script, where you want to format a suitable error message (but there are modules
	   that can help with that problem)) always check the return value from opening a file.

	   As a special case the three-argument form with a read/write mode and the third
	   argument being "undef":

	       open(my $tmp, "+>", undef) or die ...

	   opens a filehandle to an anonymous temporary file.  Also using "+<" works for
	   symmetry, but you really should consider writing something to the temporary file
	   first.  You will need to seek() to do the reading.

	   Since v5.8.0, Perl has built using PerlIO by default.  Unless you've changed this
	   (such as building Perl with "Configure -Uuseperlio"), you can open filehandles
	   directly to Perl scalars via:

	       open($fh, ">", \$variable) || ..

	   To (re)open "STDOUT" or "STDERR" as an in-memory file, close it first:

	       close STDOUT;
	       open(STDOUT, ">", \$variable)
		   or die "Can't open STDOUT: $!";

	   General examples:

	       $ARTICLE = 100;
	       open(ARTICLE) or die "Can't find article $ARTICLE: $!\n";
	       while (<ARTICLE>) {...

	       open(LOG, ">>/usr/spool/news/twitlog");	# (log is reserved)
	       # if the open fails, output is discarded

	       open(my $dbase, "+<", "dbase.mine")	# open for update
		   or die "Can't open 'dbase.mine' for update: $!";

	       open(my $dbase, "+<dbase.mine")		# ditto
		   or die "Can't open 'dbase.mine' for update: $!";

	       open(ARTICLE, "-|", "caesar <$article")	# decrypt article
		   or die "Can't start caesar: $!";

	       open(ARTICLE, "caesar <$article |")	# ditto
		   or die "Can't start caesar: $!";

	       open(EXTRACT, "|sort >Tmp$$")		# $$ is our process id
		   or die "Can't start sort: $!";

	       # in-memory files
	       open(MEMORY, ">", \$var)
		   or die "Can't open memory file: $!";
	       print MEMORY "foo!\n";			# output will appear in $var

	       # process argument list of files along with any includes

	       foreach $file (@ARGV) {
		   process($file, "fh00");
	       }

	       sub process {
		   my($filename, $input) = @_;
		   $input++;	# this is a string increment
		   unless (open($input, "<", $filename)) {
		       print STDERR "Can't open $filename: $!\n";
		       return;
		   }

		   local $_;
		   while (<$input>) {	 # note use of indirection
		       if (/^#include "(.*)"/) {
			   process($1, $input);
			   next;
		       }
		       #...	     # whatever
		   }
	       }

	   See perliol for detailed info on PerlIO.

	   You may also, in the Bourne shell tradition, specify an EXPR beginning with ">&", in
	   which case the rest of the string is interpreted as the name of a filehandle (or file
	   descriptor, if numeric) to be duped (as dup(2)) and opened.	You may use "&" after
	   ">", ">>", "<", "+>", "+>>", and "+<".  The mode you specify should match the mode of
	   the original filehandle.  (Duping a filehandle does not take into account any existing
	   contents of IO buffers.)  If you use the three-argument form, then you can pass either
	   a number, the name of a filehandle, or the normal "reference to a glob".

	   Here is a script that saves, redirects, and restores "STDOUT" and "STDERR" using
	   various methods:

	       #!/usr/bin/perl
	       open(my $oldout, ">&STDOUT")	or die "Can't dup STDOUT: $!";
	       open(OLDERR,	">&", \*STDERR) or die "Can't dup STDERR: $!";

	       open(STDOUT, '>', "foo.out") or die "Can't redirect STDOUT: $!";
	       open(STDERR, ">&STDOUT")     or die "Can't dup STDOUT: $!";

	       select STDERR; $| = 1;  # make unbuffered
	       select STDOUT; $| = 1;  # make unbuffered

	       print STDOUT "stdout 1\n";  # this works for
	       print STDERR "stderr 1\n";  # subprocesses too

	       open(STDOUT, ">&", $oldout) or die "Can't dup \$oldout: $!";
	       open(STDERR, ">&OLDERR")    or die "Can't dup OLDERR: $!";

	       print STDOUT "stdout 2\n";
	       print STDERR "stderr 2\n";

	   If you specify '<&=X', where "X" is a file descriptor number or a filehandle, then
	   Perl will do an equivalent of C's "fdopen" of that file descriptor (and not call
	   dup(2)); this is more parsimonious of file descriptors.  For example:

	       # open for input, reusing the fileno of $fd
	       open(FILEHANDLE, "<&=$fd")

	   or

	       open(FILEHANDLE, "<&=", $fd)

	   or

	       # open for append, using the fileno of OLDFH
	       open(FH, ">>&=", OLDFH)

	   or

	       open(FH, ">>&=OLDFH")

	   Being parsimonious on filehandles is also useful (besides being parsimonious) for
	   example when something is dependent on file descriptors, like for example locking
	   using flock().  If you do just "open(A, ">>&B")", the filehandle A will not have the
	   same file descriptor as B, and therefore flock(A) will not flock(B) nor vice versa.
	   But with "open(A, ">>&=B")", the filehandles will share the same underlying system
	   file descriptor.

	   Note that under Perls older than 5.8.0, Perl uses the standard C library's' fdopen()
	   to implement the "=" functionality.	On many Unix systems, fdopen() fails when file
	   descriptors exceed a certain value, typically 255.  For Perls 5.8.0 and later, PerlIO
	   is (most often) the default.

	   You can see whether your Perl was built with PerlIO by running "perl -V" and looking
	   for the "useperlio=" line.  If "useperlio" is "define", you have PerlIO; otherwise you
	   don't.

	   If you open a pipe on the command "-" (that is, specify either "|-" or "-|" with the
	   one- or two-argument forms of "open"), an implicit "fork" is done, so "open" returns
	   twice: in the parent process it returns the pid of the child process, and in the child
	   process it returns (a defined) 0.  Use "defined($pid)" or "//" to determine whether
	   the open was successful.

	   For example, use either

	       $child_pid = open(FROM_KID, "-|")   // die "can't fork: $!";

	   or
	       $child_pid = open(TO_KID,   "|-")   // die "can't fork: $!";

	   followed by

	       if ($child_pid) {
		   # am the parent:
		   # either write TO_KID or else read FROM_KID
		   ...
		   wait $child_pid;
	       } else {
		   # am the child; use STDIN/STDOUT normally
		   ...
		   exit;
	       }

	   The filehandle behaves normally for the parent, but I/O to that filehandle is piped
	   from/to the STDOUT/STDIN of the child process.  In the child process, the filehandle
	   isn't opened--I/O happens from/to the new STDOUT/STDIN.  Typically this is used like
	   the normal piped open when you want to exercise more control over just how the pipe
	   command gets executed, such as when running setuid and you don't want to have to scan
	   shell commands for metacharacters.

	   The following blocks are more or less equivalent:

	       open(FOO, "|tr '[a-z]' '[A-Z]'");
	       open(FOO, "|-", "tr '[a-z]' '[A-Z]'");
	       open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';
	       open(FOO, "|-", "tr", '[a-z]', '[A-Z]');

	       open(FOO, "cat -n '$file'|");
	       open(FOO, "-|", "cat -n '$file'");
	       open(FOO, "-|") || exec "cat", "-n", $file;
	       open(FOO, "-|", "cat", "-n", $file);

	   The last two examples in each block show the pipe as "list form", which is not yet
	   supported on all platforms.	A good rule of thumb is that if your platform has a real
	   "fork()" (in other words, if your platform is Unix, including Linux and MacOS X), you
	   can use the list form.  You would want to use the list form of the pipe so you can
	   pass literal arguments to the command without risk of the shell interpreting any shell
	   metacharacters in them.  However, this also bars you from opening pipes to commands
	   that intentionally contain shell metacharacters, such as:

	       open(FOO, "|cat -n | expand -4 | lpr")
		   // die "Can't open pipeline to lpr: $!";

	   See "Safe Pipe Opens" in perlipc for more examples of this.

	   Beginning with v5.6.0, Perl will attempt to flush all files opened for output before
	   any operation that may do a fork, but this may not be supported on some platforms (see
	   perlport).  To be safe, you may need to set $| ($AUTOFLUSH in English) or call the
	   "autoflush()" method of "IO::Handle" on any open handles.

	   On systems that support a close-on-exec flag on files, the flag will be set for the
	   newly opened file descriptor as determined by the value of $^F.  See "$^F" in perlvar.

	   Closing any piped filehandle causes the parent process to wait for the child to
	   finish, then returns the status value in $? and "${^CHILD_ERROR_NATIVE}".

	   The filename passed to the one- and two-argument forms of open() will have leading and
	   trailing whitespace deleted and normal redirection characters honored.  This property,
	   known as "magic open", can often be used to good effect.  A user could specify a
	   filename of "rsh cat file |", or you could change certain filenames as needed:

	       $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/;
	       open(FH, $filename) or die "Can't open $filename: $!";

	   Use the three-argument form to open a file with arbitrary weird characters in it,

	       open(FOO, "<", $file)
		   || die "can't open < $file: $!";

	   otherwise it's necessary to protect any leading and trailing whitespace:

	       $file =~ s#^(\s)#./$1#;
	       open(FOO, "< $file\0")
		   || die "open failed: $!";

	   (this may not work on some bizarre filesystems).  One should conscientiously choose
	   between the magic and three-argument form of open():

	       open(IN, $ARGV[0]) || die "can't open $ARGV[0]: $!";

	   will allow the user to specify an argument of the form "rsh cat file |", but will not
	   work on a filename that happens to have a trailing space, while

	       open(IN, "<", $ARGV[0])
		   || die "can't open < $ARGV[0]: $!";

	   will have exactly the opposite restrictions.

	   If you want a "real" C "open" (see open(2) on your system), then you should use the
	   "sysopen" function, which involves no such magic (but may use subtly different
	   filemodes than Perl open(), which is mapped to C fopen()).  This is another way to
	   protect your filenames from interpretation.	For example:

	       use IO::Handle;
	       sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL)
		   or die "sysopen $path: $!";
	       $oldfh = select(HANDLE); $| = 1; select($oldfh);
	       print HANDLE "stuff $$\n";
	       seek(HANDLE, 0, 0);
	       print "File contains: ", <HANDLE>;

	   Using the constructor from the "IO::Handle" package (or one of its subclasses, such as
	   "IO::File" or "IO::Socket"), you can generate anonymous filehandles that have the
	   scope of the variables used to hold them, then automatically (but silently) close once
	   their reference counts become zero, typically at scope exit:

	       use IO::File;
	       #...
	       sub read_myfile_munged {
		   my $ALL = shift;
		   # or just leave it undef to autoviv
		   my $handle = IO::File->new;
		   open($handle, "<", "myfile") or die "myfile: $!";
		   $first = <$handle>
		       or return ();	 # Automatically closed here.
		   mung($first) or die "mung failed";  # Or here.
		   return (first, <$handle>) if $ALL;  # Or here.
		   return $first;		       # Or here.
	       }

	   WARNING: The previous example has a bug because the automatic close that happens when
	   the refcount on "handle" does not properly detect and report failures.  Always close
	   the handle yourself and inspect the return value.

	       close($handle)
		   || warn "close failed: $!";

	   See "seek" for some details about mixing reading and writing.

	   Portability issues: "open" in perlport.

       opendir DIRHANDLE,EXPR
	   Opens a directory named EXPR for processing by "readdir", "telldir", "seekdir",
	   "rewinddir", and "closedir".  Returns true if successful.  DIRHANDLE may be an
	   expression whose value can be used as an indirect dirhandle, usually the real
	   dirhandle name.  If DIRHANDLE is an undefined scalar variable (or array or hash
	   element), the variable is assigned a reference to a new anonymous dirhandle; that is,
	   it's autovivified.  DIRHANDLEs have their own namespace separate from FILEHANDLEs.

	   See the example at "readdir".

       ord EXPR
       ord Returns the numeric value of the first character of EXPR.  If EXPR is an empty string,
	   returns 0.  If EXPR is omitted, uses $_.  (Note character, not byte.)

	   For the reverse, see "chr".	See perlunicode for more about Unicode.

       our EXPR
       our TYPE EXPR
       our EXPR : ATTRS
       our TYPE EXPR : ATTRS
	   "our" associates a simple name with a package variable in the current package for use
	   within the current scope.  When "use strict 'vars'" is in effect, "our" lets you use
	   declared global variables without qualifying them with package names, within the
	   lexical scope of the "our" declaration.  In this way "our" differs from "use vars",
	   which is package-scoped.

	   Unlike "my" or "state", which allocates storage for a variable and associates a simple
	   name with that storage for use within the current scope, "our" associates a simple
	   name with a package (read: global) variable in the current package, for use within the
	   current lexical scope.  In other words, "our" has the same scoping rules as "my" or
	   "state", but does not necessarily create a variable.

	   If more than one value is listed, the list must be placed in parentheses.

	       our $foo;
	       our($bar, $baz);

	   An "our" declaration declares a global variable that will be visible across its entire
	   lexical scope, even across package boundaries.  The package in which the variable is
	   entered is determined at the point of the declaration, not at the point of use.  This
	   means the following behavior holds:

	       package Foo;
	       our $bar;      # declares $Foo::bar for rest of lexical scope
	       $bar = 20;

	       package Bar;
	       print $bar;    # prints 20, as it refers to $Foo::bar

	   Multiple "our" declarations with the same name in the same lexical scope are allowed
	   if they are in different packages.  If they happen to be in the same package, Perl
	   will emit warnings if you have asked for them, just like multiple "my" declarations.
	   Unlike a second "my" declaration, which will bind the name to a fresh variable, a
	   second "our" declaration in the same package, in the same scope, is merely redundant.

	       use warnings;
	       package Foo;
	       our $bar;      # declares $Foo::bar for rest of lexical scope
	       $bar = 20;

	       package Bar;
	       our $bar = 30; # declares $Bar::bar for rest of lexical scope
	       print $bar;    # prints 30

	       our $bar;      # emits warning but has no other effect
	       print $bar;    # still prints 30

	   An "our" declaration may also have a list of attributes associated with it.

	   The exact semantics and interface of TYPE and ATTRS are still evolving.  TYPE is
	   currently bound to the use of the "fields" pragma, and attributes are handled using
	   the "attributes" pragma, or, starting from Perl 5.8.0, also via the
	   "Attribute::Handlers" module.  See "Private Variables via my()" in perlsub for
	   details, and fields, attributes, and Attribute::Handlers.

       pack TEMPLATE,LIST
	   Takes a LIST of values and converts it into a string using the rules given by the
	   TEMPLATE.  The resulting string is the concatenation of the converted values.
	   Typically, each converted value looks like its machine-level representation.  For
	   example, on 32-bit machines an integer may be represented by a sequence of 4 bytes,
	   which  will in Perl be presented as a string that's 4 characters long.

	   See perlpacktut for an introduction to this function.

	   The TEMPLATE is a sequence of characters that give the order and type of values, as
	   follows:

	       a  A string with arbitrary binary data, will be null padded.
	       A  A text (ASCII) string, will be space padded.
	       Z  A null-terminated (ASCIZ) string, will be null padded.

	       b  A bit string (ascending bit order inside each byte,
		  like vec()).
	       B  A bit string (descending bit order inside each byte).
	       h  A hex string (low nybble first).
	       H  A hex string (high nybble first).

	       c  A signed char (8-bit) value.
	       C  An unsigned char (octet) value.
	       W  An unsigned char value (can be greater than 255).

	       s  A signed short (16-bit) value.
	       S  An unsigned short value.

	       l  A signed long (32-bit) value.
	       L  An unsigned long value.

	       q  A signed quad (64-bit) value.
	       Q  An unsigned quad value.
		    (Quads are available only if your system supports 64-bit
		     integer values _and_ if Perl has been compiled to support
		     those.  Raises an exception otherwise.)

	       i  A signed integer value.
	       I  A unsigned integer value.
		    (This 'integer' is _at_least_ 32 bits wide.  Its exact
		     size depends on what a local C compiler calls 'int'.)

	       n  An unsigned short (16-bit) in "network" (big-endian) order.
	       N  An unsigned long (32-bit) in "network" (big-endian) order.
	       v  An unsigned short (16-bit) in "VAX" (little-endian) order.
	       V  An unsigned long (32-bit) in "VAX" (little-endian) order.

	       j  A Perl internal signed integer value (IV).
	       J  A Perl internal unsigned integer value (UV).

	       f  A single-precision float in native format.
	       d  A double-precision float in native format.

	       F  A Perl internal floating-point value (NV) in native format
	       D  A float of long-double precision in native format.
		    (Long doubles are available only if your system supports
		     long double values _and_ if Perl has been compiled to
		     support those.  Raises an exception otherwise.)

	       p  A pointer to a null-terminated string.
	       P  A pointer to a structure (fixed-length string).

	       u  A uuencoded string.
	       U  A Unicode character number.  Encodes to a character in char-
		  acter mode and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in
		  byte mode.

	       w  A BER compressed integer (not an ASN.1 BER, see perlpacktut
		  for details).  Its bytes represent an unsigned integer in
		  base 128, most significant digit first, with as few digits
		  as possible.	Bit eight (the high bit) is set on each byte
		  except the last.

	       x  A null byte (a.k.a ASCII NUL, "\000", chr(0))
	       X  Back up a byte.
	       @  Null-fill or truncate to absolute position, counted from the
		  start of the innermost ()-group.
	       .  Null-fill or truncate to absolute position specified by
		  the value.
	       (  Start of a ()-group.

	   One or more modifiers below may optionally follow certain letters in the TEMPLATE (the
	   second column lists letters for which the modifier is valid):

	       !   sSlLiI     Forces native (short, long, int) sizes instead
			      of fixed (16-/32-bit) sizes.

		   xX	      Make x and X act as alignment commands.

		   nNvV       Treat integers as signed instead of unsigned.

		   @.	      Specify position as byte offset in the internal
			      representation of the packed string.  Efficient
			      but dangerous.

	       >   sSiIlLqQ   Force big-endian byte-order on the type.
		   jJfFdDpP   (The "big end" touches the construct.)

	       <   sSiIlLqQ   Force little-endian byte-order on the type.
		   jJfFdDpP   (The "little end" touches the construct.)

	   The ">" and "<" modifiers can also be used on "()" groups to force a particular byte-
	   order on all components in that group, including all its subgroups.

	   The following rules apply:

	   o   Each letter may optionally be followed by a number indicating the repeat count.	A
	       numeric repeat count may optionally be enclosed in brackets, as in "pack("C[80]",
	       @arr)".	The repeat count gobbles that many values from the LIST when used with
	       all format types other than "a", "A", "Z", "b", "B", "h", "H", "@", ".", "x", "X",
	       and "P", where it means something else, described below.  Supplying a "*" for the
	       repeat count instead of a number means to use however many items are left, except
	       for:

	       o   "@", "x", and "X", where it is equivalent to 0.

	       o   <.>, where it means relative to the start of the string.

	       o   "u", where it is equivalent to 1 (or 45, which here is equivalent).

	       One can replace a numeric repeat count with a template letter enclosed in brackets
	       to use the packed byte length of the bracketed template for the repeat count.

	       For example, the template "x[L]" skips as many bytes as in a packed long, and the
	       template "$t X[$t] $t" unpacks twice whatever $t (when variable-expanded) unpacks.
	       If the template in brackets contains alignment commands (such as "x![d]"), its
	       packed length is calculated as if the start of the template had the maximal
	       possible alignment.

	       When used with "Z", a "*" as the repeat count is guaranteed to add a trailing null
	       byte, so the resulting string is always one byte longer than the byte length of
	       the item itself.

	       When used with "@", the repeat count represents an offset from the start of the
	       innermost "()" group.

	       When used with ".", the repeat count determines the starting position to calculate
	       the value offset as follows:

	       o   If the repeat count is 0, it's relative to the current position.

	       o   If the repeat count is "*", the offset is relative to the start of the packed
		   string.

	       o   And if it's an integer n, the offset is relative to the start of the nth
		   innermost "( )" group, or to the start of the string if n is bigger then the
		   group level.

	       The repeat count for "u" is interpreted as the maximal number of bytes to encode
	       per line of output, with 0, 1 and 2 replaced by 45.  The repeat count should not
	       be more than 65.

	   o   The "a", "A", and "Z" types gobble just one value, but pack it as a string of
	       length count, padding with nulls or spaces as needed.  When unpacking, "A" strips
	       trailing whitespace and nulls, "Z" strips everything after the first null, and "a"
	       returns data with no stripping at all.

	       If the value to pack is too long, the result is truncated.  If it's too long and
	       an explicit count is provided, "Z" packs only "$count-1" bytes, followed by a null
	       byte.  Thus "Z" always packs a trailing null, except when the count is 0.

	   o   Likewise, the "b" and "B" formats pack a string that's that many bits long.  Each
	       such format generates 1 bit of the result.  These are typically followed by a
	       repeat count like "B8" or "B64".

	       Each result bit is based on the least-significant bit of the corresponding input
	       character, i.e., on "ord($char)%2".  In particular, characters "0" and "1"
	       generate bits 0 and 1, as do characters "\000" and "\001".

	       Starting from the beginning of the input string, each 8-tuple of characters is
	       converted to 1 character of output.  With format "b", the first character of the
	       8-tuple determines the least-significant bit of a character; with format "B", it
	       determines the most-significant bit of a character.

	       If the length of the input string is not evenly divisible by 8, the remainder is
	       packed as if the input string were padded by null characters at the end.
	       Similarly during unpacking, "extra" bits are ignored.

	       If the input string is longer than needed, remaining characters are ignored.

	       A "*" for the repeat count uses all characters of the input field.  On unpacking,
	       bits are converted to a string of 0s and 1s.

	   o   The "h" and "H" formats pack a string that many nybbles (4-bit groups,
	       representable as hexadecimal digits, "0".."9" "a".."f") long.

	       For each such format, pack() generates 4 bits of result.  With non-alphabetical
	       characters, the result is based on the 4 least-significant bits of the input
	       character, i.e., on "ord($char)%16".  In particular, characters "0" and "1"
	       generate nybbles 0 and 1, as do bytes "\000" and "\001".  For characters "a".."f"
	       and "A".."F", the result is compatible with the usual hexadecimal digits, so that
	       "a" and "A" both generate the nybble "0xA==10".	Use only these specific hex
	       characters with this format.

	       Starting from the beginning of the template to pack(), each pair of characters is
	       converted to 1 character of output.  With format "h", the first character of the
	       pair determines the least-significant nybble of the output character; with format
	       "H", it determines the most-significant nybble.

	       If the length of the input string is not even, it behaves as if padded by a null
	       character at the end.  Similarly, "extra" nybbles are ignored during unpacking.

	       If the input string is longer than needed, extra characters are ignored.

	       A "*" for the repeat count uses all characters of the input field.  For unpack(),
	       nybbles are converted to a string of hexadecimal digits.

	   o   The "p" format packs a pointer to a null-terminated string.  You are responsible
	       for ensuring that the string is not a temporary value, as that could potentially
	       get deallocated before you got around to using the packed result.  The "P" format
	       packs a pointer to a structure of the size indicated by the length.  A null
	       pointer is created if the corresponding value for "p" or "P" is "undef"; similarly
	       with unpack(), where a null pointer unpacks into "undef".

	       If your system has a strange pointer size--meaning a pointer is neither as big as
	       an int nor as big as a long--it may not be possible to pack or unpack pointers in
	       big- or little-endian byte order.  Attempting to do so raises an exception.

	   o   The "/" template character allows packing and unpacking of a sequence of items
	       where the packed structure contains a packed item count followed by the packed
	       items themselves.  This is useful when the structure you're unpacking has encoded
	       the sizes or repeat counts for some of its fields within the structure itself as
	       separate fields.

	       For "pack", you write length-item"/"sequence-item, and the length-item describes
	       how the length value is packed.	Formats likely to be of most use are integer-
	       packing ones like "n" for Java strings, "w" for ASN.1 or SNMP, and "N" for Sun
	       XDR.

	       For "pack", sequence-item may have a repeat count, in which case the minimum of
	       that and the number of available items is used as the argument for length-item.
	       If it has no repeat count or uses a '*', the number of available items is used.

	       For "unpack", an internal stack of integer arguments unpacked so far is used.  You
	       write "/"sequence-item and the repeat count is obtained by popping off the last
	       element from the stack.	The sequence-item must not have a repeat count.

	       If sequence-item refers to a string type ("A", "a", or "Z"), the length-item is
	       the string length, not the number of strings.  With an explicit repeat count for
	       pack, the packed string is adjusted to that length.  For example:

		This code:				gives this result:

		 unpack("W/a", "\004Gurusamy")		("Guru")
		 unpack("a3/A A*", "007 Bond  J ")	(" Bond", "J")
		 unpack("a3 x2 /A A*", "007: Bond, J.") ("Bond, J", ".")

		 pack("n/a* w/a","hello,","world")     "\000\006hello,\005world"
		 pack("a/W2", ord("a") .. ord("z"))    "2ab"

	       The length-item is not returned explicitly from "unpack".

	       Supplying a count to the length-item format letter is only useful with "A", "a",
	       or "Z".	Packing with a length-item of "a" or "Z" may introduce "\000" characters,
	       which Perl does not regard as legal in numeric strings.

	   o   The integer types "s", "S", "l", and "L" may be followed by a "!" modifier to
	       specify native shorts or longs.	As shown in the example above, a bare "l" means
	       exactly 32 bits, although the native "long" as seen by the local C compiler may be
	       larger.	This is mainly an issue on 64-bit platforms.  You can see whether using
	       "!" makes any difference this way:

		   printf "format s is %d, s! is %d\n",
		       length pack("s"), length pack("s!");

		   printf "format l is %d, l! is %d\n",
		       length pack("l"), length pack("l!");

	       "i!" and "I!" are also allowed, but only for completeness' sake: they are
	       identical to "i" and "I".

	       The actual sizes (in bytes) of native shorts, ints, longs, and long longs on the
	       platform where Perl was built are also available from the command line:

		   $ perl -V:{short,int,long{,long}}size
		   shortsize='2';
		   intsize='4';
		   longsize='4';
		   longlongsize='8';

	       or programmatically via the "Config" module:

		      use Config;
		      print $Config{shortsize},    "\n";
		      print $Config{intsize},	   "\n";
		      print $Config{longsize},	   "\n";
		      print $Config{longlongsize}, "\n";

	       $Config{longlongsize} is undefined on systems without long long support.

	   o   The integer formats "s", "S", "i", "I", "l", "L", "j", and "J" are inherently non-
	       portable between processors and operating systems because they obey native
	       byteorder and endianness.  For example, a 4-byte integer 0x12345678 (305419896
	       decimal) would be ordered natively (arranged in and handled by the CPU registers)
	       into bytes as

		   0x12 0x34 0x56 0x78	# big-endian
		   0x78 0x56 0x34 0x12	# little-endian

	       Basically, Intel and VAX CPUs are little-endian, while everybody else, including
	       Motorola m68k/88k, PPC, Sparc, HP PA, Power, and Cray, are big-endian.  Alpha and
	       MIPS can be either: Digital/Compaq uses (well, used) them in little-endian mode,
	       but SGI/Cray uses them in big-endian mode.

	       The names big-endian and little-endian are comic references to the egg-eating
	       habits of the little-endian Lilliputians and the big-endian Blefuscudians from the
	       classic Jonathan Swift satire, Gulliver's Travels.  This entered computer lingo
	       via the paper "On Holy Wars and a Plea for Peace" by Danny Cohen, USC/ISI IEN 137,
	       April 1, 1980.

	       Some systems may have even weirder byte orders such as

		  0x56 0x78 0x12 0x34
		  0x34 0x12 0x78 0x56

	       You can determine your system endianness with this incantation:

		  printf("%#02x ", $_) for unpack("W*", pack L=>0x12345678);

	       The byteorder on the platform where Perl was built is also available via Config:

		   use Config;
		   print "$Config{byteorder}\n";

	       or from the command line:

		   $ perl -V:byteorder

	       Byteorders "1234" and "12345678" are little-endian; "4321" and "87654321" are big-
	       endian.

	       For portably packed integers, either use the formats "n", "N", "v", and "V" or
	       else use the ">" and "<" modifiers described immediately below.	See also
	       perlport.

	   o   Starting with Perl 5.9.2, integer and floating-point formats, along with the "p"
	       and "P" formats and "()" groups, may all be followed by the ">" or "<" endianness
	       modifiers to respectively enforce big- or little-endian byte-order.  These
	       modifiers are especially useful given how "n", "N", "v", and "V" don't cover
	       signed integers, 64-bit integers, or floating-point values.

	       Here are some concerns to keep in mind when using an endianness modifier:

	       o   Exchanging signed integers between different platforms works only when all
		   platforms store them in the same format.  Most platforms store signed integers
		   in two's-complement notation, so usually this is not an issue.

	       o   The ">" or "<" modifiers can only be used on floating-point formats on big- or
		   little-endian machines.  Otherwise, attempting to use them raises an
		   exception.

	       o   Forcing big- or little-endian byte-order on floating-point values for data
		   exchange can work only if all platforms use the same binary representation
		   such as IEEE floating-point.  Even if all platforms are using IEEE, there may
		   still be subtle differences.  Being able to use ">" or "<" on floating-point
		   values can be useful, but also dangerous if you don't know exactly what you're
		   doing.  It is not a general way to portably store floating-point values.

	       o   When using ">" or "<" on a "()" group, this affects all types inside the group
		   that accept byte-order modifiers, including all subgroups.  It is silently
		   ignored for all other types.  You are not allowed to override the byte-order
		   within a group that already has a byte-order modifier suffix.

	   o   Real numbers (floats and doubles) are in native machine format only.  Due to the
	       multiplicity of floating-point formats and the lack of a standard "network"
	       representation for them, no facility for interchange has been made.  This means
	       that packed floating-point data written on one machine may not be readable on
	       another, even if both use IEEE floating-point arithmetic (because the endianness
	       of the memory representation is not part of the IEEE spec).  See also perlport.

	       If you know exactly what you're doing, you can use the ">" or "<" modifiers to
	       force big- or little-endian byte-order on floating-point values.

	       Because Perl uses doubles (or long doubles, if configured) internally for all
	       numeric calculation, converting from double into float and thence to double again
	       loses precision, so "unpack("f", pack("f", $foo)") will not in general equal $foo.

	   o   Pack and unpack can operate in two modes: character mode ("C0" mode) where the
	       packed string is processed per character, and UTF-8 mode ("U0" mode) where the
	       packed string is processed in its UTF-8-encoded Unicode form on a byte-by-byte
	       basis.  Character mode is the default unless the format string starts with "U".
	       You can always switch mode mid-format with an explicit "C0" or "U0" in the format.
	       This mode remains in effect until the next mode change, or until the end of the
	       "()" group it (directly) applies to.

	       Using "C0" to get Unicode characters while using "U0" to get non-Unicode bytes is
	       not necessarily obvious.   Probably only the first of these is what you want:

		   $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
		     perl -CS -ne 'printf "%v04X\n", $_ for unpack("C0A*", $_)'
		   03B1.03C9
		   $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
		     perl -CS -ne 'printf "%v02X\n", $_ for unpack("U0A*", $_)'
		   CE.B1.CF.89
		   $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
		     perl -C0 -ne 'printf "%v02X\n", $_ for unpack("C0A*", $_)'
		   CE.B1.CF.89
		   $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
		     perl -C0 -ne 'printf "%v02X\n", $_ for unpack("U0A*", $_)'
		   C3.8E.C2.B1.C3.8F.C2.89

	       Those examples also illustrate that you should not try to use "pack"/"unpack" as a
	       substitute for the Encode module.

	   o   You must yourself do any alignment or padding by inserting, for example, enough
	       "x"es while packing.  There is no way for pack() and unpack() to know where
	       characters are going to or coming from, so they handle their output and input as
	       flat sequences of characters.

	   o   A "()" group is a sub-TEMPLATE enclosed in parentheses.	A group may take a repeat
	       count either as postfix, or for unpack(), also via the "/" template character.
	       Within each repetition of a group, positioning with "@" starts over at 0.
	       Therefore, the result of

		   pack("@1A((@2A)@3A)", qw[X Y Z])

	       is the string "\0X\0\0YZ".

	   o   "x" and "X" accept the "!" modifier to act as alignment commands: they jump
	       forward or back to the closest position aligned at a multiple of "count"
	       characters.  For example, to pack() or unpack() a C structure like

		   struct {
		       char   c;    /* one signed, 8-bit character */
		       double d;
		       char   cc[2];
		   }

	       one may need to use the template "c x![d] d c[2]".  This assumes that doubles must
	       be aligned to the size of double.

	       For alignment commands, a "count" of 0 is equivalent to a "count" of 1; both are
	       no-ops.

	   o   "n", "N", "v" and "V" accept the "!" modifier to represent signed 16-/32-bit
	       integers in big-/little-endian order.  This is portable only when all platforms
	       sharing packed data use the same binary representation for signed integers; for
	       example, when all platforms use two's-complement representation.

	   o   Comments can be embedded in a TEMPLATE using "#" through the end of line.  White
	       space can separate pack codes from each other, but modifiers and repeat counts
	       must follow immediately.  Breaking complex templates into individual line-by-line
	       components, suitably annotated, can do as much to improve legibility and
	       maintainability of pack/unpack formats as "/x" can for complicated pattern
	       matches.

	   o   If TEMPLATE requires more arguments than pack() is given, pack() assumes
	       additional "" arguments.  If TEMPLATE requires fewer arguments than given, extra
	       arguments are ignored.

	   Examples:

	       $foo = pack("WWWW",65,66,67,68);
	       # foo eq "ABCD"
	       $foo = pack("W4",65,66,67,68);
	       # same thing
	       $foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9);
	       # same thing with Unicode circled letters.
	       $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
	       # same thing with Unicode circled letters.  You don't get the
	       # UTF-8 bytes because the U at the start of the format caused
	       # a switch to U0-mode, so the UTF-8 bytes get joined into
	       # characters
	       $foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9);
	       # foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9"
	       # This is the UTF-8 encoding of the string in the
	       # previous example

	       $foo = pack("ccxxcc",65,66,67,68);
	       # foo eq "AB\0\0CD"

	       # NOTE: The examples above featuring "W" and "c" are true
	       # only on ASCII and ASCII-derived systems such as ISO Latin 1
	       # and UTF-8.  On EBCDIC systems, the first example would be
	       #      $foo = pack("WWWW",193,194,195,196);

	       $foo = pack("s2",1,2);
	       # "\001\000\002\000" on little-endian
	       # "\000\001\000\002" on big-endian

	       $foo = pack("a4","abcd","x","y","z");
	       # "abcd"

	       $foo = pack("aaaa","abcd","x","y","z");
	       # "axyz"

	       $foo = pack("a14","abcdefg");
	       # "abcdefg\0\0\0\0\0\0\0"

	       $foo = pack("i9pl", gmtime);
	       # a real struct tm (on my system anyway)

	       $utmp_template = "Z8 Z8 Z16 L";
	       $utmp = pack($utmp_template, @utmp1);
	       # a struct utmp (BSDish)

	       @utmp2 = unpack($utmp_template, $utmp);
	       # "@utmp1" eq "@utmp2"

	       sub bintodec {
		   unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
	       }

	       $foo = pack('sx2l', 12, 34);
	       # short 12, two zero bytes padding, long 34
	       $bar = pack('s@4l', 12, 34);
	       # short 12, zero fill to position 4, long 34
	       # $foo eq $bar
	       $baz = pack('s.l', 12, 4, 34);
	       # short 12, zero fill to position 4, long 34

	       $foo = pack('nN', 42, 4711);
	       # pack big-endian 16- and 32-bit unsigned integers
	       $foo = pack('S>L>', 42, 4711);
	       # exactly the same
	       $foo = pack('s<l<', -42, 4711);
	       # pack little-endian 16- and 32-bit signed integers
	       $foo = pack('(sl)<', -42, 4711);
	       # exactly the same

	   The same template may generally also be used in unpack().

       package NAMESPACE
       package NAMESPACE VERSION
       package NAMESPACE BLOCK
       package NAMESPACE VERSION BLOCK
	   Declares the BLOCK or the rest of the compilation unit as being in the given
	   namespace.  The scope of the package declaration is either the supplied code BLOCK or,
	   in the absence of a BLOCK, from the declaration itself through the end of current
	   scope (the enclosing block, file, or "eval").  That is, the forms without a BLOCK are
	   operative through the end of the current scope, just like the "my", "state", and "our"
	   operators.  All unqualified dynamic identifiers in this scope will be in the given
	   namespace, except where overridden by another "package" declaration or when they're
	   one of the special identifiers that qualify into "main::", like "STDOUT", "ARGV",
	   "ENV", and the punctuation variables.

	   A package statement affects dynamic variables only, including those you've used
	   "local" on, but not lexical variables, which are created with "my", "state", or "our".
	   Typically it would be the first declaration in a file included by "require" or "use".
	   You can switch into a package in more than one place, since this only determines which
	   default symbol table the compiler uses for the rest of that block.  You can refer to
	   identifiers in other packages than the current one by prefixing the identifier with
	   the package name and a double colon, as in $SomePack::var or "ThatPack::INPUT_HANDLE".
	   If package name is omitted, the "main" package as assumed.  That is, $::sail is
	   equivalent to $main::sail (as well as to "$main'sail", still seen in ancient code,
	   mostly from Perl 4).

	   If VERSION is provided, "package" sets the $VERSION variable in the given namespace to
	   a version object with the VERSION provided.	VERSION must be a "strict" style version
	   number as defined by the version module: a positive decimal number (integer or
	   decimal-fraction) without exponentiation or else a dotted-decimal v-string with a
	   leading 'v' character and at least three components.  You should set $VERSION only
	   once per package.

	   See "Packages" in perlmod for more information about packages, modules, and classes.
	   See perlsub for other scoping issues.

       __PACKAGE__
	   A special token that returns the name of the package in which it occurs.

       pipe READHANDLE,WRITEHANDLE
	   Opens a pair of connected pipes like the corresponding system call.	Note that if you
	   set up a loop of piped processes, deadlock can occur unless you are very careful.  In
	   addition, note that Perl's pipes use IO buffering, so you may need to set $| to flush
	   your WRITEHANDLE after each command, depending on the application.

	   See IPC::Open2, IPC::Open3, and "Bidirectional Communication with Another Process" in
	   perlipc for examples of such things.

	   On systems that support a close-on-exec flag on files, that flag is set on all newly
	   opened file descriptors whose "fileno"s are higher than the current value of $^F (by
	   default 2 for "STDERR").  See "$^F" in perlvar.

       pop ARRAY
       pop EXPR
       pop Pops and returns the last value of the array, shortening the array by one element.

	   Returns the undefined value if the array is empty, although this may also happen at
	   other times.  If ARRAY is omitted, pops the @ARGV array in the main program, but the
	   @_ array in subroutines, just like "shift".

	   Starting with Perl 5.14, "pop" can take a scalar EXPR, which must hold a reference to
	   an unblessed array.	The argument will be dereferenced automatically.  This aspect of
	   "pop" is considered highly experimental.  The exact behaviour may change in a future
	   version of Perl.

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.014;  # so push/pop/etc work on scalars (experimental)

       pos SCALAR
       pos Returns the offset of where the last "m//g" search left off for the variable in
	   question ($_ is used when the variable is not specified).  Note that 0 is a valid
	   match offset.  "undef" indicates that the search position is reset (usually due to
	   match failure, but can also be because no match has yet been run on the scalar).

	   "pos" directly accesses the location used by the regexp engine to store the offset, so
	   assigning to "pos" will change that offset, and so will also influence the "\G" zero-
	   width assertion in regular expressions.  Both of these effects take place for the next
	   match, so you can't affect the position with "pos" during the current match, such as
	   in "(?{pos() = 5})" or "s//pos() = 5/e".

	   Setting "pos" also resets the matched with zero-length flag, described under "Repeated
	   Patterns Matching a Zero-length Substring" in perlre.

	   Because a failed "m//gc" match doesn't reset the offset, the return from "pos" won't
	   change either in this case.	See perlre and perlop.

       print FILEHANDLE LIST
       print FILEHANDLE
       print LIST
       print
	   Prints a string or a list of strings.  Returns true if successful.  FILEHANDLE may be
	   a scalar variable containing the name of or a reference to the filehandle, thus
	   introducing one level of indirection.  (NOTE: If FILEHANDLE is a variable and the next
	   token is a term, it may be misinterpreted as an operator unless you interpose a "+" or
	   put parentheses around the arguments.)  If FILEHANDLE is omitted, prints to the last
	   selected (see "select") output handle.  If LIST is omitted, prints $_ to the currently
	   selected output handle.  To use FILEHANDLE alone to print the content of $_ to it, you
	   must use a real filehandle like "FH", not an indirect one like $fh.	To set the
	   default output handle to something other than STDOUT, use the select operation.

	   The current value of $, (if any) is printed between each LIST item.	The current value
	   of "$\" (if any) is printed after the entire LIST has been printed.	Because print
	   takes a LIST, anything in the LIST is evaluated in list context, including any
	   subroutines whose return lists you pass to "print".	Be careful not to follow the
	   print keyword with a left parenthesis unless you want the corresponding right
	   parenthesis to terminate the arguments to the print; put parentheses around all
	   arguments (or interpose a "+", but that doesn't look as good).

	   If you're storing handles in an array or hash, or in general whenever you're using any
	   expression more complex than a bareword handle or a plain, unsubscripted scalar
	   variable to retrieve it, you will have to use a block returning the filehandle value
	   instead, in which case the LIST may not be omitted:

	       print { $files[$i] } "stuff\n";
	       print { $OK ? STDOUT : STDERR } "stuff\n";

	   Printing to a closed pipe or socket will generate a SIGPIPE signal.	See perlipc for
	   more on signal handling.

       printf FILEHANDLE FORMAT, LIST
       printf FILEHANDLE
       printf FORMAT, LIST
       printf
	   Equivalent to "print FILEHANDLE sprintf(FORMAT, LIST)", except that "$\" (the output
	   record separator) is not appended.  The first argument of the list will be interpreted
	   as the "printf" format.  See sprintf for an explanation of the format argument.  If
	   you omit the LIST, $_ is used; to use FILEHANDLE without a LIST, you must use a real
	   filehandle like "FH", not an indirect one like $fh.	If "use locale" (including "use
	   locale ':not_characters'") is in effect and POSIX::setlocale() has been called, the
	   character used for the decimal separator in formatted floating-point numbers is
	   affected by the LC_NUMERIC locale setting.  See perllocale and POSIX.

	   Don't fall into the trap of using a "printf" when a simple "print" would do.  The
	   "print" is more efficient and less error prone.

       prototype FUNCTION
	   Returns the prototype of a function as a string (or "undef" if the function has no
	   prototype).	FUNCTION is a reference to, or the name of, the function whose prototype
	   you want to retrieve.

	   If FUNCTION is a string starting with "CORE::", the rest is taken as a name for a Perl
	   builtin.  If the builtin is not overridable (such as "qw//") or if its arguments
	   cannot be adequately expressed by a prototype (such as "system"), prototype() returns
	   "undef", because the builtin does not really behave like a Perl function.  Otherwise,
	   the string describing the equivalent prototype is returned.

       push ARRAY,LIST
       push EXPR,LIST
	   Treats ARRAY as a stack by appending the values of LIST to the end of ARRAY.  The
	   length of ARRAY increases by the length of LIST.  Has the same effect as

	       for $value (LIST) {
		   $ARRAY[++$#ARRAY] = $value;
	       }

	   but is more efficient.  Returns the number of elements in the array following the
	   completed "push".

	   Starting with Perl 5.14, "push" can take a scalar EXPR, which must hold a reference to
	   an unblessed array.	The argument will be dereferenced automatically.  This aspect of
	   "push" is considered highly experimental.  The exact behaviour may change in a future
	   version of Perl.

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.014;  # so push/pop/etc work on scalars (experimental)

       q/STRING/
       qq/STRING/
       qw/STRING/
       qx/STRING/
	   Generalized quotes.	See "Quote-Like Operators" in perlop.

       qr/STRING/
	   Regexp-like quote.  See "Regexp Quote-Like Operators" in perlop.

       quotemeta EXPR
       quotemeta
	   Returns the value of EXPR with all the ASCII non-"word" characters backslashed.  (That
	   is, all ASCII characters not matching "/[A-Za-z_0-9]/" will be preceded by a backslash
	   in the returned string, regardless of any locale settings.)	This is the internal
	   function implementing the "\Q" escape in double-quoted strings.  (See below for the
	   behavior on non-ASCII code points.)

	   If EXPR is omitted, uses $_.

	   quotemeta (and "\Q" ... "\E") are useful when interpolating strings into regular
	   expressions, because by default an interpolated variable will be considered a mini-
	   regular expression.	For example:

	       my $sentence = 'The quick brown fox jumped over the lazy dog';
	       my $substring = 'quick.*?fox';
	       $sentence =~ s{$substring}{big bad wolf};

	   Will cause $sentence to become 'The big bad wolf jumped over...'.

	   On the other hand:

	       my $sentence = 'The quick brown fox jumped over the lazy dog';
	       my $substring = 'quick.*?fox';
	       $sentence =~ s{\Q$substring\E}{big bad wolf};

	   Or:

	       my $sentence = 'The quick brown fox jumped over the lazy dog';
	       my $substring = 'quick.*?fox';
	       my $quoted_substring = quotemeta($substring);
	       $sentence =~ s{$quoted_substring}{big bad wolf};

	   Will both leave the sentence as is.	Normally, when accepting literal string input
	   from the user, quotemeta() or "\Q" must be used.

	   In Perl v5.14, all non-ASCII characters are quoted in non-UTF-8-encoded strings, but
	   not quoted in UTF-8 strings.

	   Starting in Perl v5.16, Perl adopted a Unicode-defined strategy for quoting non-ASCII
	   characters; the quoting of ASCII characters is unchanged.

	   Also unchanged is the quoting of non-UTF-8 strings when outside the scope of a "use
	   feature 'unicode_strings'", which is to quote all characters in the upper Latin1
	   range.  This provides complete backwards compatibility for old programs which do not
	   use Unicode.  (Note that "unicode_strings" is automatically enabled within the scope
	   of a "use v5.12" or greater.)

	   Within the scope of "use locale", all non-ASCII Latin1 code points are quoted whether
	   the string is encoded as UTF-8 or not.  As mentioned above, locale does not affect the
	   quoting of ASCII-range characters.  This protects against those locales where
	   characters such as "|" are considered to be word characters.

	   Otherwise, Perl quotes non-ASCII characters using an adaptation from Unicode (see
	   <http://www.unicode.org/reports/tr31/>.)  The only code points that are quoted are
	   those that have any of the Unicode properties:  Pattern_Syntax, Pattern_White_Space,
	   White_Space, Default_Ignorable_Code_Point, or General_Category=Control.

	   Of these properties, the two important ones are Pattern_Syntax and
	   Pattern_White_Space.  They have been set up by Unicode for exactly this purpose of
	   deciding which characters in a regular expression pattern should be quoted.	No
	   character that can be in an identifier has these properties.

	   Perl promises, that if we ever add regular expression pattern metacharacters to the
	   dozen already defined ("\ | ( ) [ { ^ $ * + ? ."), that we will only use ones that
	   have the Pattern_Syntax property.  Perl also promises, that if we ever add characters
	   that are considered to be white space in regular expressions (currently mostly
	   affected by "/x"), they will all have the Pattern_White_Space property.

	   Unicode promises that the set of code points that have these two properties will never
	   change, so something that is not quoted in v5.16 will never need to be quoted in any
	   future Perl release.  (Not all the code points that match Pattern_Syntax have actually
	   had characters assigned to them; so there is room to grow, but they are quoted whether
	   assigned or not.  Perl, of course, would never use an unassigned code point as an
	   actual metacharacter.)

	   Quoting characters that have the other 3 properties is done to enhance the readability
	   of the regular expression and not because they actually need to be quoted for regular
	   expression purposes (characters with the White_Space property are likely to be
	   indistinguishable on the page or screen from those with the Pattern_White_Space
	   property; and the other two properties contain non-printing characters).

       rand EXPR
       rand
	   Returns a random fractional number greater than or equal to 0 and less than the value
	   of EXPR.  (EXPR should be positive.)  If EXPR is omitted, the value 1 is used.
	   Currently EXPR with the value 0 is also special-cased as 1 (this was undocumented
	   before Perl 5.8.0 and is subject to change in future versions of Perl).  Automatically
	   calls "srand" unless "srand" has already been called.  See also "srand".

	   Apply "int()" to the value returned by "rand()" if you want random integers instead of
	   random fractional numbers.  For example,

	       int(rand(10))

	   returns a random integer between 0 and 9, inclusive.

	   (Note: If your rand function consistently returns numbers that are too large or too
	   small, then your version of Perl was probably compiled with the wrong number of
	   RANDBITS.)

	   "rand()" is not cryptographically secure.  You should not rely on it in security-
	   sensitive situations.  As of this writing, a number of third-party CPAN modules offer
	   random number generators intended by their authors to be cryptographically secure,
	   including: Data::Entropy, Crypt::Random, Math::Random::Secure, and Math::TrulyRandom.

       read FILEHANDLE,SCALAR,LENGTH,OFFSET
       read FILEHANDLE,SCALAR,LENGTH
	   Attempts to read LENGTH characters of data into variable SCALAR from the specified
	   FILEHANDLE.	Returns the number of characters actually read, 0 at end of file, or
	   undef if there was an error (in the latter case $! is also set).  SCALAR will be grown
	   or shrunk so that the last character actually read is the last character of the scalar
	   after the read.

	   An OFFSET may be specified to place the read data at some place in the string other
	   than the beginning.	A negative OFFSET specifies placement at that many characters
	   counting backwards from the end of the string.  A positive OFFSET greater than the
	   length of SCALAR results in the string being padded to the required size with "\0"
	   bytes before the result of the read is appended.

	   The call is implemented in terms of either Perl's or your system's native fread(3)
	   library function.  To get a true read(2) system call, see sysread.

	   Note the characters: depending on the status of the filehandle, either (8-bit) bytes
	   or characters are read.  By default, all filehandles operate on bytes, but for example
	   if the filehandle has been opened with the ":utf8" I/O layer (see "open", and the
	   "open" pragma, open), the I/O will operate on UTF8-encoded Unicode characters, not
	   bytes.  Similarly for the ":encoding" pragma: in that case pretty much any characters
	   can be read.

       readdir DIRHANDLE
	   Returns the next directory entry for a directory opened by "opendir".  If used in list
	   context, returns all the rest of the entries in the directory.  If there are no more
	   entries, returns the undefined value in scalar context and the empty list in list
	   context.

	   If you're planning to filetest the return values out of a "readdir", you'd better
	   prepend the directory in question.  Otherwise, because we didn't "chdir" there, it
	   would have been testing the wrong file.

	       opendir(my $dh, $some_dir) || die "can't opendir $some_dir: $!";
	       @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh);
	       closedir $dh;

	   As of Perl 5.11.2 you can use a bare "readdir" in a "while" loop, which will set $_ on
	   every iteration.

	       opendir(my $dh, $some_dir) || die;
	       while(readdir $dh) {
		   print "$some_dir/$_\n";
	       }
	       closedir $dh;

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious failures, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.012; # so readdir assigns to $_ in a lone while test

       readline EXPR
       readline
	   Reads from the filehandle whose typeglob is contained in EXPR (or from *ARGV if EXPR
	   is not provided).  In scalar context, each call reads and returns the next line until
	   end-of-file is reached, whereupon the subsequent call returns "undef".  In list
	   context, reads until end-of-file is reached and returns a list of lines.  Note that
	   the notion of "line" used here is whatever you may have defined with $/ or
	   $INPUT_RECORD_SEPARATOR).  See "$/" in perlvar.

	   When $/ is set to "undef", when "readline" is in scalar context (i.e., file slurp
	   mode), and when an empty file is read, it returns '' the first time, followed by
	   "undef" subsequently.

	   This is the internal function implementing the "<EXPR>" operator, but you can use it
	   directly.  The "<EXPR>" operator is discussed in more detail in "I/O Operators" in
	   perlop.

	       $line = <STDIN>;
	       $line = readline(*STDIN);    # same thing

	   If "readline" encounters an operating system error, $! will be set with the
	   corresponding error message.  It can be helpful to check $! when you are reading from
	   filehandles you don't trust, such as a tty or a socket.  The following example uses
	   the operator form of "readline" and dies if the result is not defined.

	       while ( ! eof($fh) ) {
		   defined( $_ = <$fh> ) or die "readline failed: $!";
		   ...
	       }

	   Note that you have can't handle "readline" errors that way with the "ARGV" filehandle.
	   In that case, you have to open each element of @ARGV yourself since "eof" handles
	   "ARGV" differently.

	       foreach my $arg (@ARGV) {
		   open(my $fh, $arg) or warn "Can't open $arg: $!";

		   while ( ! eof($fh) ) {
		       defined( $_ = <$fh> )
			   or die "readline failed for $arg: $!";
		       ...
		   }
	       }

       readlink EXPR
       readlink
	   Returns the value of a symbolic link, if symbolic links are implemented.  If not,
	   raises an exception.  If there is a system error, returns the undefined value and sets
	   $! (errno).	If EXPR is omitted, uses $_.

	   Portability issues: "readlink" in perlport.

       readpipe EXPR
       readpipe
	   EXPR is executed as a system command.  The collected standard output of the command is
	   returned.  In scalar context, it comes back as a single (potentially multi-line)
	   string.  In list context, returns a list of lines (however you've defined lines with
	   $/ or $INPUT_RECORD_SEPARATOR).  This is the internal function implementing the
	   "qx/EXPR/" operator, but you can use it directly.  The "qx/EXPR/" operator is
	   discussed in more detail in "I/O Operators" in perlop.  If EXPR is omitted, uses $_.

       recv SOCKET,SCALAR,LENGTH,FLAGS
	   Receives a message on a socket.  Attempts to receive LENGTH characters of data into
	   variable SCALAR from the specified SOCKET filehandle.  SCALAR will be grown or shrunk
	   to the length actually read.  Takes the same flags as the system call of the same
	   name.  Returns the address of the sender if SOCKET's protocol supports this; returns
	   an empty string otherwise.  If there's an error, returns the undefined value.  This
	   call is actually implemented in terms of recvfrom(2) system call.  See "UDP: Message
	   Passing" in perlipc for examples.

	   Note the characters: depending on the status of the socket, either (8-bit) bytes or
	   characters are received.  By default all sockets operate on bytes, but for example if
	   the socket has been changed using binmode() to operate with the ":encoding(utf8)" I/O
	   layer (see the "open" pragma, open), the I/O will operate on UTF8-encoded Unicode
	   characters, not bytes.  Similarly for the ":encoding" pragma: in that case pretty much
	   any characters can be read.

       redo LABEL
       redo
	   The "redo" command restarts the loop block without evaluating the conditional again.
	   The "continue" block, if any, is not executed.  If the LABEL is omitted, the command
	   refers to the innermost enclosing loop.  Programs that want to lie to themselves about
	   what was just input normally use this command:

	       # a simpleminded Pascal comment stripper
	       # (warning: assumes no { or } in strings)
	       LINE: while (<STDIN>) {
		   while (s|({.*}.*){.*}|$1 |) {}
		   s|{.*}| |;
		   if (s|{.*| |) {
		       $front = $_;
		       while (<STDIN>) {
			   if (/}/) {  # end of comment?
			       s|^|$front\{|;
			       redo LINE;
			   }
		       }
		   }
		   print;
	       }

	   "redo" cannot be used to retry a block that returns a value such as "eval {}", "sub
	   {}", or "do {}", and should not be used to exit a grep() or map() operation.

	   Note that a block by itself is semantically identical to a loop that executes once.
	   Thus "redo" inside such a block will effectively turn it into a looping construct.

	   See also "continue" for an illustration of how "last", "next", and "redo" work.

       ref EXPR
       ref Returns a non-empty string if EXPR is a reference, the empty string otherwise.  If
	   EXPR is not specified, $_ will be used.  The value returned depends on the type of
	   thing the reference is a reference to.  Builtin types include:

	       SCALAR
	       ARRAY
	       HASH
	       CODE
	       REF
	       GLOB
	       LVALUE
	       FORMAT
	       IO
	       VSTRING
	       Regexp

	   If the referenced object has been blessed into a package, then that package name is
	   returned instead.  You can think of "ref" as a "typeof" operator.

	       if (ref($r) eq "HASH") {
		   print "r is a reference to a hash.\n";
	       }
	       unless (ref($r)) {
		   print "r is not a reference at all.\n";
	       }

	   The return value "LVALUE" indicates a reference to an lvalue that is not a variable.
	   You get this from taking the reference of function calls like "pos()" or "substr()".
	   "VSTRING" is returned if the reference points to a version string.

	   The result "Regexp" indicates that the argument is a regular expression resulting from
	   "qr//".

	   See also perlref.

       rename OLDNAME,NEWNAME
	   Changes the name of a file; an existing file NEWNAME will be clobbered.  Returns true
	   for success, false otherwise.

	   Behavior of this function varies wildly depending on your system implementation.  For
	   example, it will usually not work across file system boundaries, even though the
	   system mv command sometimes compensates for this.  Other restrictions include whether
	   it works on directories, open files, or pre-existing files.	Check perlport and either
	   the rename(2) manpage or equivalent system documentation for details.

	   For a platform independent "move" function look at the File::Copy module.

	   Portability issues: "rename" in perlport.

       require VERSION
       require EXPR
       require
	   Demands a version of Perl specified by VERSION, or demands some semantics specified by
	   EXPR or by $_ if EXPR is not supplied.

	   VERSION may be either a numeric argument such as 5.006, which will be compared to $],
	   or a literal of the form v5.6.1, which will be compared to $^V (aka $PERL_VERSION).
	   An exception is raised if VERSION is greater than the version of the current Perl
	   interpreter.  Compare with "use", which can do a similar check at compile time.

	   Specifying VERSION as a literal of the form v5.6.1 should generally be avoided,
	   because it leads to misleading error messages under earlier versions of Perl that do
	   not support this syntax.  The equivalent numeric version should be used instead.

	       require v5.6.1;	   # run time version check
	       require 5.6.1;	   # ditto
	       require 5.006_001;  # ditto; preferred for backwards compatibility

	   Otherwise, "require" demands that a library file be included if it hasn't already been
	   included.  The file is included via the do-FILE mechanism, which is essentially just a
	   variety of "eval" with the caveat that lexical variables in the invoking script will
	   be invisible to the included code.  Has semantics similar to the following subroutine:

	       sub require {
		  my ($filename) = @_;
		  if (exists $INC{$filename}) {
		      return 1 if $INC{$filename};
		      die "Compilation failed in require";
		  }
		  my ($realfilename,$result);
		  ITER: {
		      foreach $prefix (@INC) {
			  $realfilename = "$prefix/$filename";
			  if (-f $realfilename) {
			      $INC{$filename} = $realfilename;
			      $result = do $realfilename;
			      last ITER;
			  }
		      }
		      die "Can't find $filename in \@INC";
		  }
		  if ($@) {
		      $INC{$filename} = undef;
		      die $@;
		  } elsif (!$result) {
		      delete $INC{$filename};
		      die "$filename did not return true value";
		  } else {
		      return $result;
		  }
	       }

	   Note that the file will not be included twice under the same specified name.

	   The file must return true as the last statement to indicate successful execution of
	   any initialization code, so it's customary to end such a file with "1;" unless you're
	   sure it'll return true otherwise.  But it's better just to put the "1;", in case you
	   add more statements.

	   If EXPR is a bareword, the require assumes a ".pm" extension and replaces "::" with
	   "/" in the filename for you, to make it easy to load standard modules.  This form of
	   loading of modules does not risk altering your namespace.

	   In other words, if you try this:

		   require Foo::Bar;	 # a splendid bareword

	   The require function will actually look for the "Foo/Bar.pm" file in the directories
	   specified in the @INC array.

	   But if you try this:

		   $class = 'Foo::Bar';
		   require $class;	 # $class is not a bareword
	       #or
		   require "Foo::Bar";	 # not a bareword because of the ""

	   The require function will look for the "Foo::Bar" file in the @INC array and will
	   complain about not finding "Foo::Bar" there.  In this case you can do:

		   eval "require $class";

	   Now that you understand how "require" looks for files with a bareword argument, there
	   is a little extra functionality going on behind the scenes.	Before "require" looks
	   for a ".pm" extension, it will first look for a similar filename with a ".pmc"
	   extension.  If this file is found, it will be loaded in place of any file ending in a
	   ".pm" extension.

	   You can also insert hooks into the import facility by putting Perl code directly into
	   the @INC array.  There are three forms of hooks: subroutine references, array
	   references, and blessed objects.

	   Subroutine references are the simplest case.  When the inclusion system walks through
	   @INC and encounters a subroutine, this subroutine gets called with two parameters, the
	   first a reference to itself, and the second the name of the file to be included (e.g.,
	   "Foo/Bar.pm").  The subroutine should return either nothing or else a list of up to
	   three values in the following order:

	   1.  A filehandle, from which the file will be read.

	   2.  A reference to a subroutine.  If there is no filehandle (previous item), then this
	       subroutine is expected to generate one line of source code per call, writing the
	       line into $_ and returning 1, then finally at end of file returning 0.  If there
	       is a filehandle, then the subroutine will be called to act as a simple source
	       filter, with the line as read in $_.  Again, return 1 for each valid line, and 0
	       after all lines have been returned.

	   3.  Optional state for the subroutine.  The state is passed in as $_[1].  A reference
	       to the subroutine itself is passed in as $_[0].

	   If an empty list, "undef", or nothing that matches the first 3 values above is
	   returned, then "require" looks at the remaining elements of @INC.  Note that this
	   filehandle must be a real filehandle (strictly a typeglob or reference to a typeglob,
	   whether blessed or unblessed); tied filehandles will be ignored and processing will
	   stop there.

	   If the hook is an array reference, its first element must be a subroutine reference.
	   This subroutine is called as above, but the first parameter is the array reference.
	   This lets you indirectly pass arguments to the subroutine.

	   In other words, you can write:

	       push @INC, \&my_sub;
	       sub my_sub {
		   my ($coderef, $filename) = @_;  # $coderef is \&my_sub
		   ...
	       }

	   or:

	       push @INC, [ \&my_sub, $x, $y, ... ];
	       sub my_sub {
		   my ($arrayref, $filename) = @_;
		   # Retrieve $x, $y, ...
		   my @parameters = @$arrayref[1..$#$arrayref];
		   ...
	       }

	   If the hook is an object, it must provide an INC method that will be called as above,
	   the first parameter being the object itself.  (Note that you must fully qualify the
	   sub's name, as unqualified "INC" is always forced into package "main".)  Here is a
	   typical code layout:

	       # In Foo.pm
	       package Foo;
	       sub new { ... }
	       sub Foo::INC {
		   my ($self, $filename) = @_;
		   ...
	       }

	       # In the main program
	       push @INC, Foo->new(...);

	   These hooks are also permitted to set the %INC entry corresponding to the files they
	   have loaded.  See "%INC" in perlvar.

	   For a yet-more-powerful import facility, see "use" and perlmod.

       reset EXPR
       reset
	   Generally used in a "continue" block at the end of a loop to clear variables and reset
	   "??" searches so that they work again.  The expression is interpreted as a list of
	   single characters (hyphens allowed for ranges).  All variables and arrays beginning
	   with one of those letters are reset to their pristine state.  If the expression is
	   omitted, one-match searches ("?pattern?") are reset to match again.	Only resets
	   variables or searches in the current package.  Always returns 1.  Examples:

	       reset 'X';      # reset all X variables
	       reset 'a-z';    # reset lower case variables
	       reset;	       # just reset ?one-time? searches

	   Resetting "A-Z" is not recommended because you'll wipe out your @ARGV and @INC arrays
	   and your %ENV hash.	Resets only package variables; lexical variables are unaffected,
	   but they clean themselves up on scope exit anyway, so you'll probably want to use them
	   instead.  See "my".

       return EXPR
       return
	   Returns from a subroutine, "eval", or "do FILE" with the value given in EXPR.
	   Evaluation of EXPR may be in list, scalar, or void context, depending on how the
	   return value will be used, and the context may vary from one execution to the next
	   (see "wantarray").  If no EXPR is given, returns an empty list in list context, the
	   undefined value in scalar context, and (of course) nothing at all in void context.

	   (In the absence of an explicit "return", a subroutine, eval, or do FILE automatically
	   returns the value of the last expression evaluated.)

       reverse LIST
	   In list context, returns a list value consisting of the elements of LIST in the
	   opposite order.  In scalar context, concatenates the elements of LIST and returns a
	   string value with all characters in the opposite order.

	       print join(", ", reverse "world", "Hello"); # Hello, world

	       print scalar reverse "dlrow ,", "olleH";    # Hello, world

	   Used without arguments in scalar context, reverse() reverses $_.

	       $_ = "dlrow ,olleH";
	       print reverse;				   # No output, list context
	       print scalar reverse;			   # Hello, world

	   Note that reversing an array to itself (as in "@a = reverse @a") will preserve non-
	   existent elements whenever possible, i.e., for non magical arrays or tied arrays with
	   "EXISTS" and "DELETE" methods.

	   This operator is also handy for inverting a hash, although there are some caveats.  If
	   a value is duplicated in the original hash, only one of those can be represented as a
	   key in the inverted hash.  Also, this has to unwind one hash and build a whole new
	   one, which may take some time on a large hash, such as from a DBM file.

	       %by_name = reverse %by_address;	# Invert the hash

       rewinddir DIRHANDLE
	   Sets the current position to the beginning of the directory for the "readdir" routine
	   on DIRHANDLE.

	   Portability issues: "rewinddir" in perlport.

       rindex STR,SUBSTR,POSITION
       rindex STR,SUBSTR
	   Works just like index() except that it returns the position of the last occurrence of
	   SUBSTR in STR.  If POSITION is specified, returns the last occurrence beginning at or
	   before that position.

       rmdir FILENAME
       rmdir
	   Deletes the directory specified by FILENAME if that directory is empty.  If it
	   succeeds it returns true; otherwise it returns false and sets $! (errno).  If FILENAME
	   is omitted, uses $_.

	   To remove a directory tree recursively ("rm -rf" on Unix) look at the "rmtree"
	   function of the File::Path module.

       s///
	   The substitution operator.  See "Regexp Quote-Like Operators" in perlop.

       say FILEHANDLE LIST
       say FILEHANDLE
       say LIST
       say Just like "print", but implicitly appends a newline.  "say LIST" is simply an
	   abbreviation for "{ local $\ = "\n"; print LIST }".	To use FILEHANDLE without a LIST
	   to print the contents of $_ to it, you must use a real filehandle like "FH", not an
	   indirect one like $fh.

	   This keyword is available only when the "say" feature is enabled, or when prefixed
	   with "CORE::"; see feature.	Alternately, include a "use v5.10" or later to the
	   current scope.

       scalar EXPR
	   Forces EXPR to be interpreted in scalar context and returns the value of EXPR.

	       @counts = ( scalar @a, scalar @b, scalar @c );

	   There is no equivalent operator to force an expression to be interpolated in list
	   context because in practice, this is never needed.  If you really wanted to do so,
	   however, you could use the construction "@{[ (some expression) ]}", but usually a
	   simple "(some expression)" suffices.

	   Because "scalar" is a unary operator, if you accidentally use a parenthesized list for
	   the EXPR, this behaves as a scalar comma expression, evaluating all but the last
	   element in void context and returning the final element evaluated in scalar context.
	   This is seldom what you want.

	   The following single statement:

	       print uc(scalar(&foo,$bar)),$baz;

	   is the moral equivalent of these two:

	       &foo;
	       print(uc($bar),$baz);

	   See perlop for more details on unary operators and the comma operator.

       seek FILEHANDLE,POSITION,WHENCE
	   Sets FILEHANDLE's position, just like the "fseek" call of "stdio".  FILEHANDLE may be
	   an expression whose value gives the name of the filehandle.	The values for WHENCE are
	   0 to set the new position in bytes to POSITION; 1 to set it to the current position
	   plus POSITION; and 2 to set it to EOF plus POSITION, typically negative.  For WHENCE
	   you may use the constants "SEEK_SET", "SEEK_CUR", and "SEEK_END" (start of the file,
	   current position, end of the file) from the Fcntl module.  Returns 1 on success, false
	   otherwise.

	   Note the in bytes: even if the filehandle has been set to operate on characters (for
	   example by using the ":encoding(utf8)" open layer), tell() will return byte offsets,
	   not character offsets (because implementing that would render seek() and tell() rather
	   slow).

	   If you want to position the file for "sysread" or "syswrite", don't use "seek",
	   because buffering makes its effect on the file's read-write position unpredictable and
	   non-portable.  Use "sysseek" instead.

	   Due to the rules and rigors of ANSI C, on some systems you have to do a seek whenever
	   you switch between reading and writing.  Amongst other things, this may have the
	   effect of calling stdio's clearerr(3).  A WHENCE of 1 ("SEEK_CUR") is useful for not
	   moving the file position:

	       seek(TEST,0,1);

	   This is also useful for applications emulating "tail -f".  Once you hit EOF on your
	   read and then sleep for a while, you (probably) have to stick in a dummy seek() to
	   reset things.  The "seek" doesn't change the position, but it does clear the end-of-
	   file condition on the handle, so that the next "<FILE>" makes Perl try again to read
	   something.  (We hope.)

	   If that doesn't work (some I/O implementations are particularly cantankerous), you
	   might need something like this:

	       for (;;) {
		   for ($curpos = tell(FILE); $_ = <FILE>;
			$curpos = tell(FILE)) {
		       # search for some stuff and put it into files
		   }
		   sleep($for_a_while);
		   seek(FILE, $curpos, 0);
	       }

       seekdir DIRHANDLE,POS
	   Sets the current position for the "readdir" routine on DIRHANDLE.  POS must be a value
	   returned by "telldir".  "seekdir" also has the same caveats about possible directory
	   compaction as the corresponding system library routine.

       select FILEHANDLE
       select
	   Returns the currently selected filehandle.  If FILEHANDLE is supplied, sets the new
	   current default filehandle for output.  This has two effects: first, a "write" or a
	   "print" without a filehandle default to this FILEHANDLE.  Second, references to
	   variables related to output will refer to this output channel.

	   For example, to set the top-of-form format for more than one output channel, you might
	   do the following:

	       select(REPORT1);
	       $^ = 'report1_top';
	       select(REPORT2);
	       $^ = 'report2_top';

	   FILEHANDLE may be an expression whose value gives the name of the actual filehandle.
	   Thus:

	       $oldfh = select(STDERR); $| = 1; select($oldfh);

	   Some programmers may prefer to think of filehandles as objects with methods,
	   preferring to write the last example as:

	       use IO::Handle;
	       STDERR->autoflush(1);

	   Portability issues: "select" in perlport.

       select RBITS,WBITS,EBITS,TIMEOUT
	   This calls the select(2) syscall with the bit masks specified, which can be
	   constructed using "fileno" and "vec", along these lines:

	       $rin = $win = $ein = '';
	       vec($rin, fileno(STDIN),  1) = 1;
	       vec($win, fileno(STDOUT), 1) = 1;
	       $ein = $rin | $win;

	   If you want to select on many filehandles, you may wish to write a subroutine like
	   this:

	       sub fhbits {
		   my @fhlist = @_;
		   my $bits = "";
		   for my $fh (@fhlist) {
		       vec($bits, fileno($fh), 1) = 1;
		   }
		   return $bits;
	       }
	       $rin = fhbits(*STDIN, *TTY, *MYSOCK);

	   The usual idiom is:

	       ($nfound,$timeleft) =
		 select($rout=$rin, $wout=$win, $eout=$ein, $timeout);

	   or to block until something becomes ready just do this

	       $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);

	   Most systems do not bother to return anything useful in $timeleft, so calling select()
	   in scalar context just returns $nfound.

	   Any of the bit masks can also be undef.  The timeout, if specified, is in seconds,
	   which may be fractional.  Note: not all implementations are capable of returning the
	   $timeleft.  If not, they always return $timeleft equal to the supplied $timeout.

	   You can effect a sleep of 250 milliseconds this way:

	       select(undef, undef, undef, 0.25);

	   Note that whether "select" gets restarted after signals (say, SIGALRM) is
	   implementation-dependent.  See also perlport for notes on the portability of "select".

	   On error, "select" behaves just like select(2): it returns -1 and sets $!.

	   On some Unixes, select(2) may report a socket file descriptor as "ready for reading"
	   even when no data is available, and thus any subsequent "read" would block.	This can
	   be avoided if you always use O_NONBLOCK on the socket.  See select(2) and fcntl(2) for
	   further details.

	   The standard "IO::Select" module provides a user-friendlier interface to "select",
	   mostly because it does all the bit-mask work for you.

	   WARNING: One should not attempt to mix buffered I/O (like "read" or <FH>) with
	   "select", except as permitted by POSIX, and even then only on POSIX systems.  You have
	   to use "sysread" instead.

	   Portability issues: "select" in perlport.

       semctl ID,SEMNUM,CMD,ARG
	   Calls the System V IPC function semctl(2).  You'll probably have to say

	       use IPC::SysV;

	   first to get the correct constant definitions.  If CMD is IPC_STAT or GETALL, then ARG
	   must be a variable that will hold the returned semid_ds structure or semaphore value
	   array.  Returns like "ioctl": the undefined value for error, ""0 but true"" for zero,
	   or the actual return value otherwise.  The ARG must consist of a vector of native
	   short integers, which may be created with "pack("s!",(0)x$nsem)".  See also "SysV IPC"
	   in perlipc, "IPC::SysV", "IPC::Semaphore" documentation.

	   Portability issues: "semctl" in perlport.

       semget KEY,NSEMS,FLAGS
	   Calls the System V IPC function semget(2).  Returns the semaphore id, or the undefined
	   value on error.  See also "SysV IPC" in perlipc, "IPC::SysV", "IPC::SysV::Semaphore"
	   documentation.

	   Portability issues: "semget" in perlport.

       semop KEY,OPSTRING
	   Calls the System V IPC function semop(2) for semaphore operations such as signalling
	   and waiting.  OPSTRING must be a packed array of semop structures.  Each semop
	   structure can be generated with "pack("s!3", $semnum, $semop, $semflag)".  The length
	   of OPSTRING implies the number of semaphore operations.  Returns true if successful,
	   false on error.  As an example, the following code waits on semaphore $semnum of
	   semaphore id $semid:

	       $semop = pack("s!3", $semnum, -1, 0);
	       die "Semaphore trouble: $!\n" unless semop($semid, $semop);

	   To signal the semaphore, replace "-1" with 1.  See also "SysV IPC" in perlipc,
	   "IPC::SysV", and "IPC::SysV::Semaphore" documentation.

	   Portability issues: "semop" in perlport.

       send SOCKET,MSG,FLAGS,TO
       send SOCKET,MSG,FLAGS
	   Sends a message on a socket.  Attempts to send the scalar MSG to the SOCKET
	   filehandle.	Takes the same flags as the system call of the same name.  On unconnected
	   sockets, you must specify a destination to send to, in which case it does a sendto(2)
	   syscall.  Returns the number of characters sent, or the undefined value on error.  The
	   sendmsg(2) syscall is currently unimplemented.  See "UDP: Message Passing" in perlipc
	   for examples.

	   Note the characters: depending on the status of the socket, either (8-bit) bytes or
	   characters are sent.  By default all sockets operate on bytes, but for example if the
	   socket has been changed using binmode() to operate with the ":encoding(utf8)" I/O
	   layer (see "open", or the "open" pragma, open), the I/O will operate on UTF-8 encoded
	   Unicode characters, not bytes.  Similarly for the ":encoding" pragma: in that case
	   pretty much any characters can be sent.

       setpgrp PID,PGRP
	   Sets the current process group for the specified PID, 0 for the current process.
	   Raises an exception when used on a machine that doesn't implement POSIX setpgid(2) or
	   BSD setpgrp(2).  If the arguments are omitted, it defaults to "0,0".  Note that the
	   BSD 4.2 version of "setpgrp" does not accept any arguments, so only "setpgrp(0,0)" is
	   portable.  See also "POSIX::setsid()".

	   Portability issues: "setpgrp" in perlport.

       setpriority WHICH,WHO,PRIORITY
	   Sets the current priority for a process, a process group, or a user.  (See
	   setpriority(2).)  Raises an exception when used on a machine that doesn't implement
	   setpriority(2).

	   Portability issues: "setpriority" in perlport.

       setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
	   Sets the socket option requested.  Returns "undef" on error.  Use integer constants
	   provided by the "Socket" module for LEVEL and OPNAME.  Values for LEVEL can also be
	   obtained from getprotobyname.  OPTVAL might either be a packed string or an integer.
	   An integer OPTVAL is shorthand for pack("i", OPTVAL).

	   An example disabling Nagle's algorithm on a socket:

	       use Socket qw(IPPROTO_TCP TCP_NODELAY);
	       setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1);

	   Portability issues: "setsockopt" in perlport.

       shift ARRAY
       shift EXPR
       shift
	   Shifts the first value of the array off and returns it, shortening the array by 1 and
	   moving everything down.  If there are no elements in the array, returns the undefined
	   value.  If ARRAY is omitted, shifts the @_ array within the lexical scope of
	   subroutines and formats, and the @ARGV array outside a subroutine and also within the
	   lexical scopes established by the "eval STRING", "BEGIN {}", "INIT {}", "CHECK {}",
	   "UNITCHECK {}", and "END {}" constructs.

	   Starting with Perl 5.14, "shift" can take a scalar EXPR, which must hold a reference
	   to an unblessed array.  The argument will be dereferenced automatically.  This aspect
	   of "shift" is considered highly experimental.  The exact behaviour may change in a
	   future version of Perl.

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.014;  # so push/pop/etc work on scalars (experimental)

	   See also "unshift", "push", and "pop".  "shift" and "unshift" do the same thing to the
	   left end of an array that "pop" and "push" do to the right end.

       shmctl ID,CMD,ARG
	   Calls the System V IPC function shmctl.  You'll probably have to say

	       use IPC::SysV;

	   first to get the correct constant definitions.  If CMD is "IPC_STAT", then ARG must be
	   a variable that will hold the returned "shmid_ds" structure.  Returns like ioctl:
	   "undef" for error; "0 but true" for zero; and the actual return value otherwise.  See
	   also "SysV IPC" in perlipc and "IPC::SysV" documentation.

	   Portability issues: "shmctl" in perlport.

       shmget KEY,SIZE,FLAGS
	   Calls the System V IPC function shmget.  Returns the shared memory segment id, or
	   "undef" on error.  See also "SysV IPC" in perlipc and "IPC::SysV" documentation.

	   Portability issues: "shmget" in perlport.

       shmread ID,VAR,POS,SIZE
       shmwrite ID,STRING,POS,SIZE
	   Reads or writes the System V shared memory segment ID starting at position POS for
	   size SIZE by attaching to it, copying in/out, and detaching from it.  When reading,
	   VAR must be a variable that will hold the data read.  When writing, if STRING is too
	   long, only SIZE bytes are used; if STRING is too short, nulls are written to fill out
	   SIZE bytes.	Return true if successful, false on error.  shmread() taints the
	   variable.  See also "SysV IPC" in perlipc, "IPC::SysV", and the "IPC::Shareable"
	   module from CPAN.

	   Portability issues: "shmread" in perlport and "shmwrite" in perlport.

       shutdown SOCKET,HOW
	   Shuts down a socket connection in the manner indicated by HOW, which has the same
	   interpretation as in the syscall of the same name.

	       shutdown(SOCKET, 0);    # I/we have stopped reading data
	       shutdown(SOCKET, 1);    # I/we have stopped writing data
	       shutdown(SOCKET, 2);    # I/we have stopped using this socket

	   This is useful with sockets when you want to tell the other side you're done writing
	   but not done reading, or vice versa.  It's also a more insistent form of close because
	   it also disables the file descriptor in any forked copies in other processes.

	   Returns 1 for success; on error, returns "undef" if the first argument is not a valid
	   filehandle, or returns 0 and sets $! for any other failure.

       sin EXPR
       sin Returns the sine of EXPR (expressed in radians).  If EXPR is omitted, returns sine of
	   $_.

	   For the inverse sine operation, you may use the "Math::Trig::asin" function, or use
	   this relation:

	       sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }

       sleep EXPR
       sleep
	   Causes the script to sleep for (integer) EXPR seconds, or forever if no argument is
	   given.  Returns the integer number of seconds actually slept.

	   May be interrupted if the process receives a signal such as "SIGALRM".

	       eval {
		   local $SIG{ALARM} = sub { die "Alarm!\n" };
		   sleep;
	       };
	       die $@ unless $@ eq "Alarm!\n";

	   You probably cannot mix "alarm" and "sleep" calls, because "sleep" is often
	   implemented using "alarm".

	   On some older systems, it may sleep up to a full second less than what you requested,
	   depending on how it counts seconds.	Most modern systems always sleep the full amount.
	   They may appear to sleep longer than that, however, because your process might not be
	   scheduled right away in a busy multitasking system.

	   For delays of finer granularity than one second, the Time::HiRes module (from CPAN,
	   and starting from Perl 5.8 part of the standard distribution) provides usleep().  You
	   may also use Perl's four-argument version of select() leaving the first three
	   arguments undefined, or you might be able to use the "syscall" interface to access
	   setitimer(2) if your system supports it.  See perlfaq8 for details.

	   See also the POSIX module's "pause" function.

       socket SOCKET,DOMAIN,TYPE,PROTOCOL
	   Opens a socket of the specified kind and attaches it to filehandle SOCKET.  DOMAIN,
	   TYPE, and PROTOCOL are specified the same as for the syscall of the same name.  You
	   should "use Socket" first to get the proper definitions imported.  See the examples in
	   "Sockets: Client/Server Communication" in perlipc.

	   On systems that support a close-on-exec flag on files, the flag will be set for the
	   newly opened file descriptor, as determined by the value of $^F.  See "$^F" in
	   perlvar.

       socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
	   Creates an unnamed pair of sockets in the specified domain, of the specified type.
	   DOMAIN, TYPE, and PROTOCOL are specified the same as for the syscall of the same name.
	   If unimplemented, raises an exception.  Returns true if successful.

	   On systems that support a close-on-exec flag on files, the flag will be set for the
	   newly opened file descriptors, as determined by the value of $^F.  See "$^F" in
	   perlvar.

	   Some systems defined "pipe" in terms of "socketpair", in which a call to "pipe(Rdr,
	   Wtr)" is essentially:

	       use Socket;
	       socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
	       shutdown(Rdr, 1);	# no more writing for reader
	       shutdown(Wtr, 0);	# no more reading for writer

	   See perlipc for an example of socketpair use.  Perl 5.8 and later will emulate
	   socketpair using IP sockets to localhost if your system implements sockets but not
	   socketpair.

	   Portability issues: "socketpair" in perlport.

       sort SUBNAME LIST
       sort BLOCK LIST
       sort LIST
	   In list context, this sorts the LIST and returns the sorted list value.  In scalar
	   context, the behaviour of "sort()" is undefined.

	   If SUBNAME or BLOCK is omitted, "sort"s in standard string comparison order.  If
	   SUBNAME is specified, it gives the name of a subroutine that returns an integer less
	   than, equal to, or greater than 0, depending on how the elements of the list are to be
	   ordered.  (The "<=>" and "cmp" operators are extremely useful in such routines.)
	   SUBNAME may be a scalar variable name (unsubscripted), in which case the value
	   provides the name of (or a reference to) the actual subroutine to use.  In place of a
	   SUBNAME, you can provide a BLOCK as an anonymous, in-line sort subroutine.

	   If the subroutine's prototype is "($$)", the elements to be compared are passed by
	   reference in @_, as for a normal subroutine.  This is slower than unprototyped
	   subroutines, where the elements to be compared are passed into the subroutine as the
	   package global variables $a and $b (see example below).  Note that in the latter case,
	   it is usually highly counter-productive to declare $a and $b as lexicals.

	   If the subroutine is an XSUB, the elements to be compared are pushed on to the stack,
	   the way arguments are usually passed to XSUBs.  $a and $b are not set.

	   The values to be compared are always passed by reference and should not be modified.

	   You also cannot exit out of the sort block or subroutine using any of the loop control
	   operators described in perlsyn or with "goto".

	   When "use locale" (but not "use locale 'not_characters'") is in effect, "sort LIST"
	   sorts LIST according to the current collation locale.  See perllocale.

	   sort() returns aliases into the original list, much as a for loop's index variable
	   aliases the list elements.  That is, modifying an element of a list returned by sort()
	   (for example, in a "foreach", "map" or "grep") actually modifies the element in the
	   original list.  This is usually something to be avoided when writing clear code.

	   Perl 5.6 and earlier used a quicksort algorithm to implement sort.  That algorithm was
	   not stable, so could go quadratic.  (A stable sort preserves the input order of
	   elements that compare equal.  Although quicksort's run time is O(NlogN) when averaged
	   over all arrays of length N, the time can be O(N**2), quadratic behavior, for some
	   inputs.)  In 5.7, the quicksort implementation was replaced with a stable mergesort
	   algorithm whose worst-case behavior is O(NlogN).  But benchmarks indicated that for
	   some inputs, on some platforms, the original quicksort was faster.  5.8 has a sort
	   pragma for limited control of the sort.  Its rather blunt control of the underlying
	   algorithm may not persist into future Perls, but the ability to characterize the input
	   or output in implementation independent ways quite probably will.  See the sort
	   pragma.

	   Examples:

	       # sort lexically
	       @articles = sort @files;

	       # same thing, but with explicit sort routine
	       @articles = sort {$a cmp $b} @files;

	       # now case-insensitively
	       @articles = sort {fc($a) cmp fc($b)} @files;

	       # same thing in reversed order
	       @articles = sort {$b cmp $a} @files;

	       # sort numerically ascending
	       @articles = sort {$a <=> $b} @files;

	       # sort numerically descending
	       @articles = sort {$b <=> $a} @files;

	       # this sorts the %age hash by value instead of key
	       # using an in-line function
	       @eldest = sort { $age{$b} <=> $age{$a} } keys %age;

	       # sort using explicit subroutine name
	       sub byage {
		   $age{$a} <=> $age{$b};  # presuming numeric
	       }
	       @sortedclass = sort byage @class;

	       sub backwards { $b cmp $a }
	       @harry  = qw(dog cat x Cain Abel);
	       @george = qw(gone chased yz Punished Axed);
	       print sort @harry;
		   # prints AbelCaincatdogx
	       print sort backwards @harry;
		   # prints xdogcatCainAbel
	       print sort @george, 'to', @harry;
		   # prints AbelAxedCainPunishedcatchaseddoggonetoxyz

	       # inefficiently sort by descending numeric compare using
	       # the first integer after the first = sign, or the
	       # whole record case-insensitively otherwise

	       my @new = sort {
		   ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
				       ||
			       fc($a)  cmp  fc($b)
	       } @old;

	       # same thing, but much more efficiently;
	       # we'll build auxiliary indices instead
	       # for speed
	       my @nums = @caps = ();
	       for (@old) {
		   push @nums, ( /=(\d+)/ ? $1 : undef );
		   push @caps, fc($_);
	       }

	       my @new = @old[ sort {
				      $nums[$b] <=> $nums[$a]
					       ||
				      $caps[$a] cmp $caps[$b]
				    } 0..$#old
			     ];

	       # same thing, but without any temps
	       @new = map { $_->[0] }
		      sort { $b->[1] <=> $a->[1]
				      ||
			     $a->[2] cmp $b->[2]
		      } map { [$_, /=(\d+)/, fc($_)] } @old;

	       # using a prototype allows you to use any comparison subroutine
	       # as a sort subroutine (including other package's subroutines)
	       package other;
	       sub backwards ($$) { $_[1] cmp $_[0]; }	# $a and $b are not set here

	       package main;
	       @new = sort other::backwards @old;

	       # guarantee stability, regardless of algorithm
	       use sort 'stable';
	       @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

	       # force use of mergesort (not portable outside Perl 5.8)
	       use sort '_mergesort';  # note discouraging _
	       @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

	   Warning: syntactical care is required when sorting the list returned from a function.
	   If you want to sort the list returned by the function call "find_records(@key)", you
	   can use:

	       @contact = sort { $a cmp $b } find_records @key;
	       @contact = sort +find_records(@key);
	       @contact = sort &find_records(@key);
	       @contact = sort(find_records(@key));

	   If instead you want to sort the array @key with the comparison routine
	   "find_records()" then you can use:

	       @contact = sort { find_records() } @key;
	       @contact = sort find_records(@key);
	       @contact = sort(find_records @key);
	       @contact = sort(find_records (@key));

	   If you're using strict, you must not declare $a and $b as lexicals.	They are package
	   globals.  That means that if you're in the "main" package and type

	       @articles = sort {$b <=> $a} @files;

	   then $a and $b are $main::a and $main::b (or $::a and $::b), but if you're in the
	   "FooPack" package, it's the same as typing

	       @articles = sort {$FooPack::b <=> $FooPack::a} @files;

	   The comparison function is required to behave.  If it returns inconsistent results
	   (sometimes saying $x[1] is less than $x[2] and sometimes saying the opposite, for
	   example) the results are not well-defined.

	   Because "<=>" returns "undef" when either operand is "NaN" (not-a-number), be careful
	   when sorting with a comparison function like "$a <=> $b" any lists that might contain
	   a "NaN".  The following example takes advantage that "NaN != NaN" to eliminate any
	   "NaN"s from the input list.

	       @result = sort { $a <=> $b } grep { $_ == $_ } @input;

       splice ARRAY or EXPR,OFFSET,LENGTH,LIST
       splice ARRAY or EXPR,OFFSET,LENGTH
       splice ARRAY or EXPR,OFFSET
       splice ARRAY or EXPR
	   Removes the elements designated by OFFSET and LENGTH from an array, and replaces them
	   with the elements of LIST, if any.  In list context, returns the elements removed from
	   the array.  In scalar context, returns the last element removed, or "undef" if no
	   elements are removed.  The array grows or shrinks as necessary.  If OFFSET is negative
	   then it starts that far from the end of the array.  If LENGTH is omitted, removes
	   everything from OFFSET onward.  If LENGTH is negative, removes the elements from
	   OFFSET onward except for -LENGTH elements at the end of the array.  If both OFFSET and
	   LENGTH are omitted, removes everything.  If OFFSET is past the end of the array, Perl
	   issues a warning, and splices at the end of the array.

	   The following equivalences hold (assuming "$#a >= $i" )

	       push(@a,$x,$y)	   splice(@a,@a,0,$x,$y)
	       pop(@a)		   splice(@a,-1)
	       shift(@a)	   splice(@a,0,1)
	       unshift(@a,$x,$y)   splice(@a,0,0,$x,$y)
	       $a[$i] = $y	   splice(@a,$i,1,$y)

	   Example, assuming array lengths are passed before arrays:

	       sub aeq {  # compare two list values
		   my(@a) = splice(@_,0,shift);
		   my(@b) = splice(@_,0,shift);
		   return 0 unless @a == @b;  # same len?
		   while (@a) {
		       return 0 if pop(@a) ne pop(@b);
		   }
		   return 1;
	       }
	       if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }

	   Starting with Perl 5.14, "splice" can take scalar EXPR, which must hold a reference to
	   an unblessed array.	The argument will be dereferenced automatically.  This aspect of
	   "splice" is considered highly experimental.	The exact behaviour may change in a
	   future version of Perl.

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.014;  # so push/pop/etc work on scalars (experimental)

       split /PATTERN/,EXPR,LIMIT
       split /PATTERN/,EXPR
       split /PATTERN/
       split
	   Splits the string EXPR into a list of strings and returns the list in list context, or
	   the size of the list in scalar context.

	   If only PATTERN is given, EXPR defaults to $_.

	   Anything in EXPR that matches PATTERN is taken to be a separator that separates the
	   EXPR into substrings (called "fields") that do not include the separator.  Note that a
	   separator may be longer than one character or even have no characters at all (the
	   empty string, which is a zero-width match).

	   The PATTERN need not be constant; an expression may be used to specify a pattern that
	   varies at runtime.

	   If PATTERN matches the empty string, the EXPR is split at the match position (between
	   characters).  As an example, the following:

	       print join(':', split('b', 'abc')), "\n";

	   uses the 'b' in 'abc' as a separator to produce the output 'a:c'.  However, this:

	       print join(':', split('', 'abc')), "\n";

	   uses empty string matches as separators to produce the output 'a:b:c'; thus, the empty
	   string may be used to split EXPR into a list of its component characters.

	   As a special case for "split", the empty pattern given in match operator syntax ("//")
	   specifically matches the empty string, which is contrary to its usual interpretation
	   as the last successful match.

	   If PATTERN is "/^/", then it is treated as if it used the multiline modifier ("/^/m"),
	   since it isn't much use otherwise.

	   As another special case, "split" emulates the default behavior of the command line
	   tool awk when the PATTERN is either omitted or a literal string composed of a single
	   space character (such as ' ' or "\x20", but not e.g. "/ /").  In this case, any
	   leading whitespace in EXPR is removed before splitting occurs, and the PATTERN is
	   instead treated as if it were "/\s+/"; in particular, this means that any contiguous
	   whitespace (not just a single space character) is used as a separator.  However, this
	   special treatment can be avoided by specifying the pattern "/ /" instead of the string
	   " ", thereby allowing only a single space character to be a separator.

	   If omitted, PATTERN defaults to a single space, " ", triggering the previously
	   described awk emulation.

	   If LIMIT is specified and positive, it represents the maximum number of fields into
	   which the EXPR may be split; in other words, LIMIT is one greater than the maximum
	   number of times EXPR may be split.  Thus, the LIMIT value 1 means that EXPR may be
	   split a maximum of zero times, producing a maximum of one field (namely, the entire
	   value of EXPR).  For instance:

	       print join(':', split(//, 'abc', 1)), "\n";

	   produces the output 'abc', and this:

	       print join(':', split(//, 'abc', 2)), "\n";

	   produces the output 'a:bc', and each of these:

	       print join(':', split(//, 'abc', 3)), "\n";
	       print join(':', split(//, 'abc', 4)), "\n";

	   produces the output 'a:b:c'.

	   If LIMIT is negative, it is treated as if it were instead arbitrarily large; as many
	   fields as possible are produced.

	   If LIMIT is omitted (or, equivalently, zero), then it is usually treated as if it were
	   instead negative but with the exception that trailing empty fields are stripped (empty
	   leading fields are always preserved); if all fields are empty, then all fields are
	   considered to be trailing (and are thus stripped in this case).  Thus, the following:

	       print join(':', split(',', 'a,b,c,,,')), "\n";

	   produces the output 'a:b:c', but the following:

	       print join(':', split(',', 'a,b,c,,,', -1)), "\n";

	   produces the output 'a:b:c:::'.

	   In time-critical applications, it is worthwhile to avoid splitting into more fields
	   than necessary.  Thus, when assigning to a list, if LIMIT is omitted (or zero), then
	   LIMIT is treated as though it were one larger than the number of variables in the
	   list; for the following, LIMIT is implicitly 4:

	       ($login, $passwd, $remainder) = split(/:/);

	   Note that splitting an EXPR that evaluates to the empty string always produces zero
	   fields, regardless of the LIMIT specified.

	   An empty leading field is produced when there is a positive-width match at the
	   beginning of EXPR.  For instance:

	       print join(':', split(/ /, ' abc')), "\n";

	   produces the output ':abc'.	However, a zero-width match at the beginning of EXPR
	   never produces an empty field, so that:

	       print join(':', split(//, ' abc'));

	   produces the output ' :a:b:c' (rather than ': :a:b:c').

	   An empty trailing field, on the other hand, is produced when there is a match at the
	   end of EXPR, regardless of the length of the match (of course, unless a non-zero LIMIT
	   is given explicitly, such fields are removed, as in the last example).  Thus:

	       print join(':', split(//, ' abc', -1)), "\n";

	   produces the output ' :a:b:c:'.

	   If the PATTERN contains capturing groups, then for each separator, an additional field
	   is produced for each substring captured by a group (in the order in which the groups
	   are specified, as per backreferences); if any group does not match, then it captures
	   the "undef" value instead of a substring.  Also, note that any such additional field
	   is produced whenever there is a separator (that is, whenever a split occurs), and such
	   an additional field does not count towards the LIMIT.  Consider the following
	   expressions evaluated in list context (each returned list is provided in the
	   associated comment):

	       split(/-|,/, "1-10,20", 3)
	       # ('1', '10', '20')

	       split(/(-|,)/, "1-10,20", 3)
	       # ('1', '-', '10', ',', '20')

	       split(/-|(,)/, "1-10,20", 3)
	       # ('1', undef, '10', ',', '20')

	       split(/(-)|,/, "1-10,20", 3)
	       # ('1', '-', '10', undef, '20')

	       split(/(-)|(,)/, "1-10,20", 3)
	       # ('1', '-', undef, '10', undef, ',', '20')

       sprintf FORMAT, LIST
	   Returns a string formatted by the usual "printf" conventions of the C library function
	   "sprintf".  See below for more details and see sprintf(3) or printf(3) on your system
	   for an explanation of the general principles.

	   For example:

		   # Format number with up to 8 leading zeroes
		   $result = sprintf("%08d", $number);

		   # Round number to 3 digits after decimal point
		   $rounded = sprintf("%.3f", $number);

	   Perl does its own "sprintf" formatting: it emulates the C function sprintf(3), but
	   doesn't use it except for floating-point numbers, and even then only standard
	   modifiers are allowed.  Non-standard extensions in your local sprintf(3) are therefore
	   unavailable from Perl.

	   Unlike "printf", "sprintf" does not do what you probably mean when you pass it an
	   array as your first argument.  The array is given scalar context, and instead of using
	   the 0th element of the array as the format, Perl will use the count of elements in the
	   array as the format, which is almost never useful.

	   Perl's "sprintf" permits the following universally-known conversions:

	      %%    a percent sign
	      %c    a character with the given number
	      %s    a string
	      %d    a signed integer, in decimal
	      %u    an unsigned integer, in decimal
	      %o    an unsigned integer, in octal
	      %x    an unsigned integer, in hexadecimal
	      %e    a floating-point number, in scientific notation
	      %f    a floating-point number, in fixed decimal notation
	      %g    a floating-point number, in %e or %f notation

	   In addition, Perl permits the following widely-supported conversions:

	      %X    like %x, but using upper-case letters
	      %E    like %e, but using an upper-case "E"
	      %G    like %g, but with an upper-case "E" (if applicable)
	      %b    an unsigned integer, in binary
	      %B    like %b, but using an upper-case "B" with the # flag
	      %p    a pointer (outputs the Perl value's address in hexadecimal)
	      %n    special: *stores* the number of characters output so far
		    into the next argument in the parameter list

	   Finally, for backward (and we do mean "backward") compatibility, Perl permits these
	   unnecessary but widely-supported conversions:

	      %i    a synonym for %d
	      %D    a synonym for %ld
	      %U    a synonym for %lu
	      %O    a synonym for %lo
	      %F    a synonym for %f

	   Note that the number of exponent digits in the scientific notation produced by %e, %E,
	   %g and %G for numbers with the modulus of the exponent less than 100 is system-
	   dependent: it may be three or less (zero-padded as necessary).  In other words, 1.23
	   times ten to the 99th may be either "1.23e99" or "1.23e099".

	   Between the "%" and the format letter, you may specify several additional attributes
	   controlling the interpretation of the format.  In order, these are:

	   format parameter index
	       An explicit format parameter index, such as "2$".  By default sprintf will format
	       the next unused argument in the list, but this allows you to take the arguments
	       out of order:

		 printf '%2$d %1$d', 12, 34;	  # prints "34 12"
		 printf '%3$d %d %1$d', 1, 2, 3;  # prints "3 1 1"

	   flags
	       one or more of:

		  space   prefix non-negative number with a space
		  +	  prefix non-negative number with a plus sign
		  -	  left-justify within the field
		  0	  use zeros, not spaces, to right-justify
		  #	  ensure the leading "0" for any octal,
			  prefix non-zero hexadecimal with "0x" or "0X",
			  prefix non-zero binary with "0b" or "0B"

	       For example:

		 printf '<% d>',  12;	# prints "< 12>"
		 printf '<%+d>',  12;	# prints "<+12>"
		 printf '<%6s>',  12;	# prints "<    12>"
		 printf '<%-6s>', 12;	# prints "<12	 >"
		 printf '<%06s>', 12;	# prints "<000012>"
		 printf '<%#o>',  12;	# prints "<014>"
		 printf '<%#x>',  12;	# prints "<0xc>"
		 printf '<%#X>',  12;	# prints "<0XC>"
		 printf '<%#b>',  12;	# prints "<0b1100>"
		 printf '<%#B>',  12;	# prints "<0B1100>"

	       When a space and a plus sign are given as the flags at once, a plus sign is used
	       to prefix a positive number.

		 printf '<%+ d>', 12;	# prints "<+12>"
		 printf '<% +d>', 12;	# prints "<+12>"

	       When the # flag and a precision are given in the %o conversion, the precision is
	       incremented if it's necessary for the leading "0".

		 printf '<%#.5o>', 012;      # prints "<00012>"
		 printf '<%#.5o>', 012345;   # prints "<012345>"
		 printf '<%#.0o>', 0;	     # prints "<0>"

	   vector flag
	       This flag tells Perl to interpret the supplied string as a vector of integers, one
	       for each character in the string.  Perl applies the format to each integer in
	       turn, then joins the resulting strings with a separator (a dot "." by default).
	       This can be useful for displaying ordinal values of characters in arbitrary
	       strings:

		 printf "%vd", "AB\x{100}";	      # prints "65.66.256"
		 printf "version is v%vd\n", $^V;     # Perl's version

	       Put an asterisk "*" before the "v" to override the string to use to separate the
	       numbers:

		 printf "address is %*vX\n", ":", $addr;   # IPv6 address
		 printf "bits are %0*v8b\n", " ", $bits;   # random bitstring

	       You can also explicitly specify the argument number to use for the join string
	       using something like "*2$v"; for example:

		 printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":";   # 3 IPv6 addresses

	   (minimum) width
	       Arguments are usually formatted to be only as wide as required to display the
	       given value.  You can override the width by putting a number here, or get the
	       width from the next argument (with "*") or from a specified argument (e.g., with
	       "*2$"):

		 printf "<%s>", "a";	   # prints "<a>"
		 printf "<%6s>", "a";	   # prints "<	   a>"
		 printf "<%*s>", 6, "a";   # prints "<	   a>"
		 printf "<%*2$s>", "a", 6; # prints "<	   a>"
		 printf "<%2s>", "long";   # prints "<long>" (does not truncate)

	       If a field width obtained through "*" is negative, it has the same effect as the
	       "-" flag: left-justification.

	   precision, or maximum width
	       You can specify a precision (for numeric conversions) or a maximum width (for
	       string conversions) by specifying a "." followed by a number.  For floating-point
	       formats except "g" and "G", this specifies how many places right of the decimal
	       point to show (the default being 6).  For example:

		 # these examples are subject to system-specific variation
		 printf '<%f>', 1;    # prints "<1.000000>"
		 printf '<%.1f>', 1;  # prints "<1.0>"
		 printf '<%.0f>', 1;  # prints "<1>"
		 printf '<%e>', 10;   # prints "<1.000000e+01>"
		 printf '<%.1e>', 10; # prints "<1.0e+01>"

	       For "g" and "G", this specifies the maximum number of digits to show, including
	       those prior to the decimal point and those after it; for example:

		 # These examples are subject to system-specific variation.
		 printf '<%g>', 1;	  # prints "<1>"
		 printf '<%.10g>', 1;	  # prints "<1>"
		 printf '<%g>', 100;	  # prints "<100>"
		 printf '<%.1g>', 100;	  # prints "<1e+02>"
		 printf '<%.2g>', 100.01; # prints "<1e+02>"
		 printf '<%.5g>', 100.01; # prints "<100.01>"
		 printf '<%.4g>', 100.01; # prints "<100>"

	       For integer conversions, specifying a precision implies that the output of the
	       number itself should be zero-padded to this width, where the 0 flag is ignored:

		 printf '<%.6d>', 1;	  # prints "<000001>"
		 printf '<%+.6d>', 1;	  # prints "<+000001>"
		 printf '<%-10.6d>', 1;   # prints "<000001    >"
		 printf '<%10.6d>', 1;	  # prints "<	 000001>"
		 printf '<%010.6d>', 1;   # prints "<	 000001>"
		 printf '<%+10.6d>', 1;   # prints "<	+000001>"

		 printf '<%.6x>', 1;	  # prints "<000001>"
		 printf '<%#.6x>', 1;	  # prints "<0x000001>"
		 printf '<%-10.6x>', 1;   # prints "<000001    >"
		 printf '<%10.6x>', 1;	  # prints "<	 000001>"
		 printf '<%010.6x>', 1;   # prints "<	 000001>"
		 printf '<%#10.6x>', 1;   # prints "<  0x000001>"

	       For string conversions, specifying a precision truncates the string to fit the
	       specified width:

		 printf '<%.5s>', "truncated";	 # prints "<trunc>"
		 printf '<%10.5s>', "truncated"; # prints "<	 trunc>"

	       You can also get the precision from the next argument using ".*":

		 printf '<%.6x>', 1;	   # prints "<000001>"
		 printf '<%.*x>', 6, 1;    # prints "<000001>"

	       If a precision obtained through "*" is negative, it counts as having no precision
	       at all.

		 printf '<%.*s>',  7, "string";   # prints "<string>"
		 printf '<%.*s>',  3, "string";   # prints "<str>"
		 printf '<%.*s>',  0, "string";   # prints "<>"
		 printf '<%.*s>', -1, "string";   # prints "<string>"

		 printf '<%.*d>',  1, 0;   # prints "<0>"
		 printf '<%.*d>',  0, 0;   # prints "<>"
		 printf '<%.*d>', -1, 0;   # prints "<0>"

	       You cannot currently get the precision from a specified number, but it is intended
	       that this will be possible in the future, for example using ".*2$":

		 printf "<%.*2$x>", 1, 6;   # INVALID, but in future will print "<000001>"

	   size
	       For numeric conversions, you can specify the size to interpret the number as using
	       "l", "h", "V", "q", "L", or "ll".  For integer conversions ("d u o x X b i D U
	       O"), numbers are usually assumed to be whatever the default integer size is on
	       your platform (usually 32 or 64 bits), but you can override this to use instead
	       one of the standard C types, as supported by the compiler used to build Perl:

		  hh	      interpret integer as C type "char" or "unsigned char"
			      on Perl 5.14 or later
		  h	      interpret integer as C type "short" or "unsigned short"
		  j	      interpret integer as C type "intmax_t" on Perl 5.14
			      or later, and only with a C99 compiler (unportable)
		  l	      interpret integer as C type "long" or "unsigned long"
		  q, L, or ll interpret integer as C type "long long", "unsigned long long",
			      or "quad" (typically 64-bit integers)
		  t	      interpret integer as C type "ptrdiff_t" on Perl 5.14 or later
		  z	      interpret integer as C type "size_t" on Perl 5.14 or later

	       As of 5.14, none of these raises an exception if they are not supported on your
	       platform.  However, if warnings are enabled, a warning of the "printf" warning
	       class is issued on an unsupported conversion flag.  Should you instead prefer an
	       exception, do this:

		   use warnings FATAL => "printf";

	       If you would like to know about a version dependency before you start running the
	       program, put something like this at its top:

		   use 5.014;  # for hh/j/t/z/ printf modifiers

	       You can find out whether your Perl supports quads via Config:

		   use Config;
		   if ($Config{use64bitint} eq "define" || $Config{longsize} >= 8) {
		       print "Nice quads!\n";
		   }

	       For floating-point conversions ("e f g E F G"), numbers are usually assumed to be
	       the default floating-point size on your platform (double or long double), but you
	       can force "long double" with "q", "L", or "ll" if your platform supports them.
	       You can find out whether your Perl supports long doubles via Config:

		   use Config;
		   print "long doubles\n" if $Config{d_longdbl} eq "define";

	       You can find out whether Perl considers "long double" to be the default floating-
	       point size to use on your platform via Config:

		   use Config;
		   if ($Config{uselongdouble} eq "define") {
		       print "long doubles by default\n";
		   }

	       It can also be that long doubles and doubles are the same thing:

		       use Config;
		       ($Config{doublesize} == $Config{longdblsize}) &&
			       print "doubles are long doubles\n";

	       The size specifier "V" has no effect for Perl code, but is supported for
	       compatibility with XS code.  It means "use the standard size for a Perl integer or
	       floating-point number", which is the default.

	   order of arguments
	       Normally, sprintf() takes the next unused argument as the value to format for each
	       format specification.  If the format specification uses "*" to require additional
	       arguments, these are consumed from the argument list in the order they appear in
	       the format specification before the value to format.  Where an argument is
	       specified by an explicit index, this does not affect the normal order for the
	       arguments, even when the explicitly specified index would have been the next
	       argument.

	       So:

		   printf "<%*.*s>", $a, $b, $c;

	       uses $a for the width, $b for the precision, and $c as the value to format; while:

		 printf "<%*1$.*s>", $a, $b;

	       would use $a for the width and precision, and $b as the value to format.

	       Here are some more examples; be aware that when using an explicit index, the "$"
	       may need escaping:

		 printf "%2\$d %d\n",	 12, 34;	# will print "34 12\n"
		 printf "%2\$d %d %d\n", 12, 34;	# will print "34 12 34\n"
		 printf "%3\$d %d %d\n", 12, 34, 56;	# will print "56 12 34\n"
		 printf "%2\$*3\$d %d\n", 12, 34, 3;	# will print " 34 12\n"

	   If "use locale" (including "use locale 'not_characters'") is in effect and
	   POSIX::setlocale() has been called, the character used for the decimal separator in
	   formatted floating-point numbers is affected by the LC_NUMERIC locale.  See perllocale
	   and POSIX.

       sqrt EXPR
       sqrt
	   Return the positive square root of EXPR.  If EXPR is omitted, uses $_.  Works only for
	   non-negative operands unless you've loaded the "Math::Complex" module.

	       use Math::Complex;
	       print sqrt(-4);	  # prints 2i

       srand EXPR
       srand
	   Sets and returns the random number seed for the "rand" operator.

	   The point of the function is to "seed" the "rand" function so that "rand" can produce
	   a different sequence each time you run your program.  When called with a parameter,
	   "srand" uses that for the seed; otherwise it (semi-)randomly chooses a seed.  In
	   either case, starting with Perl 5.14, it returns the seed.  To signal that your code
	   will work only on Perls of a recent vintage:

	       use 5.014;  # so srand returns the seed

	   If "srand()" is not called explicitly, it is called implicitly without a parameter at
	   the first use of the "rand" operator.  However, this was not true of versions of Perl
	   before 5.004, so if your script will run under older Perl versions, it should call
	   "srand"; otherwise most programs won't call "srand()" at all.

	   But there are a few situations in recent Perls where programs are likely to want to
	   call "srand".  One is for generating predictable results generally for testing or
	   debugging.  There, you use "srand($seed)", with the same $seed each time.  Another
	   case is that you may want to call "srand()" after a "fork()" to avoid child processes
	   sharing the same seed value as the parent (and consequently each other).

	   Do not call "srand()" (i.e., without an argument) more than once per process.  The
	   internal state of the random number generator should contain more entropy than can be
	   provided by any seed, so calling "srand()" again actually loses randomness.

	   Most implementations of "srand" take an integer and will silently truncate decimal
	   numbers.  This means "srand(42)" will usually produce the same results as
	   "srand(42.1)".  To be safe, always pass "srand" an integer.

	   In versions of Perl prior to 5.004 the default seed was just the current "time".  This
	   isn't a particularly good seed, so many old programs supply their own seed value
	   (often "time ^ $$" or "time ^ ($$ + ($$ << 15))"), but that isn't necessary any more.

	   Frequently called programs (like CGI scripts) that simply use

	       time ^ $$

	   for a seed can fall prey to the mathematical property that

	       a^b == (a+1)^(b+1)

	   one-third of the time.  So don't do that.

	   A typical use of the returned seed is for a test program which has too many
	   combinations to test comprehensively in the time available to it each run.  It can
	   test a random subset each time, and should there be a failure, log the seed used for
	   that run so that it can later be used to reproduce the same results.

	   "rand()" is not cryptographically secure.  You should not rely on it in security-
	   sensitive situations.  As of this writing, a number of third-party CPAN modules offer
	   random number generators intended by their authors to be cryptographically secure,
	   including: Data::Entropy, Crypt::Random, Math::Random::Secure, and Math::TrulyRandom.

       stat FILEHANDLE
       stat EXPR
       stat DIRHANDLE
       stat
	   Returns a 13-element list giving the status info for a file, either the file opened
	   via FILEHANDLE or DIRHANDLE, or named by EXPR.  If EXPR is omitted, it stats $_ (not
	   "_"!).  Returns the empty list if "stat" fails.  Typically used as follows:

	       ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
		  $atime,$mtime,$ctime,$blksize,$blocks)
		      = stat($filename);

	   Not all fields are supported on all filesystem types.  Here are the meanings of the
	   fields:

	     0 dev	device number of filesystem
	     1 ino	inode number
	     2 mode	file mode  (type and permissions)
	     3 nlink	number of (hard) links to the file
	     4 uid	numeric user ID of file's owner
	     5 gid	numeric group ID of file's owner
	     6 rdev	the device identifier (special files only)
	     7 size	total size of file, in bytes
	     8 atime	last access time in seconds since the epoch
	     9 mtime	last modify time in seconds since the epoch
	    10 ctime	inode change time in seconds since the epoch (*)
	    11 blksize	preferred block size for file system I/O
	    12 blocks	actual number of blocks allocated

	   (The epoch was at 00:00 January 1, 1970 GMT.)

	   (*) Not all fields are supported on all filesystem types.  Notably, the ctime field is
	   non-portable.  In particular, you cannot expect it to be a "creation time"; see "Files
	   and Filesystems" in perlport for details.

	   If "stat" is passed the special filehandle consisting of an underline, no stat is
	   done, but the current contents of the stat structure from the last "stat", "lstat", or
	   filetest are returned.  Example:

	       if (-x $file && (($d) = stat(_)) && $d < 0) {
		   print "$file is executable NFS file\n";
	       }

	   (This works on machines only for which the device number is negative under NFS.)

	   Because the mode contains both the file type and its permissions, you should mask off
	   the file type portion and (s)printf using a "%o" if you want to see the real
	   permissions.

	       $mode = (stat($filename))[2];
	       printf "Permissions are %04o\n", $mode & 07777;

	   In scalar context, "stat" returns a boolean value indicating success or failure, and,
	   if successful, sets the information associated with the special filehandle "_".

	   The File::stat module provides a convenient, by-name access mechanism:

	       use File::stat;
	       $sb = stat($filename);
	       printf "File is %s, size is %s, perm %04o, mtime %s\n",
		      $filename, $sb->size, $sb->mode & 07777,
		      scalar localtime $sb->mtime;

	   You can import symbolic mode constants ("S_IF*") and functions ("S_IS*") from the
	   Fcntl module:

	       use Fcntl ':mode';

	       $mode = (stat($filename))[2];

	       $user_rwx      = ($mode & S_IRWXU) >> 6;
	       $group_read    = ($mode & S_IRGRP) >> 3;
	       $other_execute =  $mode & S_IXOTH;

	       printf "Permissions are %04o\n", S_IMODE($mode), "\n";

	       $is_setuid     =  $mode & S_ISUID;
	       $is_directory  =  S_ISDIR($mode);

	   You could write the last two using the "-u" and "-d" operators.  Commonly available
	   "S_IF*" constants are:

	       # Permissions: read, write, execute, for user, group, others.

	       S_IRWXU S_IRUSR S_IWUSR S_IXUSR
	       S_IRWXG S_IRGRP S_IWGRP S_IXGRP
	       S_IRWXO S_IROTH S_IWOTH S_IXOTH

	       # Setuid/Setgid/Stickiness/SaveText.
	       # Note that the exact meaning of these is system-dependent.

	       S_ISUID S_ISGID S_ISVTX S_ISTXT

	       # File types.  Not all are necessarily available on
	       # your system.

	       S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR
	       S_IFIFO S_IFSOCK S_IFWHT S_ENFMT

	       # The following are compatibility aliases for S_IRUSR,
	       # S_IWUSR, and S_IXUSR.

	       S_IREAD S_IWRITE S_IEXEC

	   and the "S_IF*" functions are

	       S_IMODE($mode)	 the part of $mode containing the permission
				 bits and the setuid/setgid/sticky bits

	       S_IFMT($mode)	 the part of $mode containing the file type
				 which can be bit-anded with (for example)
				 S_IFREG or with the following functions

	       # The operators -f, -d, -l, -b, -c, -p, and -S.

	       S_ISREG($mode) S_ISDIR($mode) S_ISLNK($mode)
	       S_ISBLK($mode) S_ISCHR($mode) S_ISFIFO($mode) S_ISSOCK($mode)

	       # No direct -X operator counterpart, but for the first one
	       # the -g operator is often equivalent.  The ENFMT stands for
	       # record flocking enforcement, a platform-dependent feature.

	       S_ISENFMT($mode) S_ISWHT($mode)

	   See your native chmod(2) and stat(2) documentation for more details about the "S_*"
	   constants.  To get status info for a symbolic link instead of the target file behind
	   the link, use the "lstat" function.

	   Portability issues: "stat" in perlport.

       state EXPR
       state TYPE EXPR
       state EXPR : ATTRS
       state TYPE EXPR : ATTRS
	   "state" declares a lexically scoped variable, just like "my".  However, those
	   variables will never be reinitialized, contrary to lexical variables that are
	   reinitialized each time their enclosing block is entered.  See "Persistent Private
	   Variables" in perlsub for details.

	   "state" variables are enabled only when the "use feature "state"" pragma is in effect,
	   unless the keyword is written as "CORE::state".  See also feature.

       study SCALAR
       study
	   Takes extra time to study SCALAR ($_ if unspecified) in anticipation of doing many
	   pattern matches on the string before it is next modified.  This may or may not save
	   time, depending on the nature and number of patterns you are searching and the
	   distribution of character frequencies in the string to be searched; you probably want
	   to compare run times with and without it to see which is faster.  Those loops that
	   scan for many short constant strings (including the constant parts of more complex
	   patterns) will benefit most.  (The way "study" works is this: a linked list of every
	   character in the string to be searched is made, so we know, for example, where all the
	   'k' characters are.	From each search string, the rarest character is selected, based
	   on some static frequency tables constructed from some C programs and English text.
	   Only those places that contain this "rarest" character are examined.)

	   For example, here is a loop that inserts index producing entries before any line
	   containing a certain pattern:

	       while (<>) {
		   study;
		   print ".IX foo\n"	if /\bfoo\b/;
		   print ".IX bar\n"	if /\bbar\b/;
		   print ".IX blurfl\n" if /\bblurfl\b/;
		   # ...
		   print;
	       }

	   In searching for "/\bfoo\b/", only locations in $_ that contain "f" will be looked at,
	   because "f" is rarer than "o".  In general, this is a big win except in pathological
	   cases.  The only question is whether it saves you more time than it took to build the
	   linked list in the first place.

	   Note that if you have to look for strings that you don't know till runtime, you can
	   build an entire loop as a string and "eval" that to avoid recompiling all your
	   patterns all the time.  Together with undefining $/ to input entire files as one
	   record, this can be quite fast, often faster than specialized programs like fgrep(1).
	   The following scans a list of files (@files) for a list of words (@words), and prints
	   out the names of those files that contain a match:

	       $search = 'while (<>) { study;';
	       foreach $word (@words) {
		   $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
	       }
	       $search .= "}";
	       @ARGV = @files;
	       undef $/;
	       eval $search;	    # this screams
	       $/ = "\n";	 # put back to normal input delimiter
	       foreach $file (sort keys(%seen)) {
		   print $file, "\n";
	       }

       sub NAME BLOCK
       sub NAME (PROTO) BLOCK
       sub NAME : ATTRS BLOCK
       sub NAME (PROTO) : ATTRS BLOCK
	   This is subroutine definition, not a real function per se.  Without a BLOCK it's just
	   a forward declaration.  Without a NAME, it's an anonymous function declaration, so
	   does return a value: the CODE ref of the closure just created.

	   See perlsub and perlref for details about subroutines and references; see attributes
	   and Attribute::Handlers for more information about attributes.

       __SUB__
	   A special token that returns the a reference to the current subroutine, or "undef"
	   outside of a subroutine.

	   This token is only available under "use v5.16" or the "current_sub" feature.  See
	   feature.

       substr EXPR,OFFSET,LENGTH,REPLACEMENT
       substr EXPR,OFFSET,LENGTH
       substr EXPR,OFFSET
	   Extracts a substring out of EXPR and returns it.  First character is at offset zero.
	   If OFFSET is negative, starts that far back from the end of the string.  If LENGTH is
	   omitted, returns everything through the end of the string.  If LENGTH is negative,
	   leaves that many characters off the end of the string.

	       my $s = "The black cat climbed the green tree";
	       my $color  = substr $s, 4, 5;	  # black
	       my $middle = substr $s, 4, -11;	  # black cat climbed the
	       my $end	  = substr $s, 14;	  # climbed the green tree
	       my $tail   = substr $s, -4;	  # tree
	       my $z	  = substr $s, -4, 2;	  # tr

	   You can use the substr() function as an lvalue, in which case EXPR must itself be an
	   lvalue.  If you assign something shorter than LENGTH, the string will shrink, and if
	   you assign something longer than LENGTH, the string will grow to accommodate it.  To
	   keep the string the same length, you may need to pad or chop your value using
	   "sprintf".

	   If OFFSET and LENGTH specify a substring that is partly outside the string, only the
	   part within the string is returned.	If the substring is beyond either end of the
	   string, substr() returns the undefined value and produces a warning.  When used as an
	   lvalue, specifying a substring that is entirely outside the string raises an
	   exception.  Here's an example showing the behavior for boundary cases:

	       my $name = 'fred';
	       substr($name, 4) = 'dy'; 	# $name is now 'freddy'
	       my $null = substr $name, 6, 2;	# returns "" (no warning)
	       my $oops = substr $name, 7;	# returns undef, with warning
	       substr($name, 7) = 'gap';	# raises an exception

	   An alternative to using substr() as an lvalue is to specify the replacement string as
	   the 4th argument.  This allows you to replace parts of the EXPR and return what was
	   there before in one operation, just as you can with splice().

	       my $s = "The black cat climbed the green tree";
	       my $z = substr $s, 14, 7, "jumped from";    # climbed
	       # $s is now "The black cat jumped from the green tree"

	   Note that the lvalue returned by the three-argument version of substr() acts as a
	   'magic bullet'; each time it is assigned to, it remembers which part of the original
	   string is being modified; for example:

	       $x = '1234';
	       for (substr($x,1,2)) {
		   $_ = 'a';   print $x,"\n";	 # prints 1a4
		   $_ = 'xyz'; print $x,"\n";	 # prints 1xyz4
		   $x = '56789';
		   $_ = 'pq';  print $x,"\n";	 # prints 5pq9
	       }

	   With negative offsets, it remembers its position from the end of the string when the
	   target string is modified:

	       $x = '1234';
	       for (substr($x, -3, 2)) {
		   $_ = 'a';   print $x,"\n";	 # prints 1a4, as above
		   $x = 'abcdefg';
		   print $_,"\n";		 # prints f
	       }

	   Prior to Perl version 5.10, the result of using an lvalue multiple times was
	   unspecified.  Prior to 5.16, the result with negative offsets was unspecified.

       symlink OLDFILE,NEWFILE
	   Creates a new filename symbolically linked to the old filename.  Returns 1 for
	   success, 0 otherwise.  On systems that don't support symbolic links, raises an
	   exception.  To check for that, use eval:

	       $symlink_exists = eval { symlink("",""); 1 };

	   Portability issues: "symlink" in perlport.

       syscall NUMBER, LIST
	   Calls the system call specified as the first element of the list, passing the
	   remaining elements as arguments to the system call.	If unimplemented, raises an
	   exception.  The arguments are interpreted as follows: if a given argument is numeric,
	   the argument is passed as an int.  If not, the pointer to the string value is passed.
	   You are responsible to make sure a string is pre-extended long enough to receive any
	   result that might be written into a string.	You can't use a string literal (or other
	   read-only string) as an argument to "syscall" because Perl has to assume that any
	   string pointer might be written through.  If your integer arguments are not literals
	   and have never been interpreted in a numeric context, you may need to add 0 to them to
	   force them to look like numbers.  This emulates the "syswrite" function (or vice
	   versa):

	       require 'syscall.ph';	    # may need to run h2ph
	       $s = "hi there\n";
	       syscall(&SYS_write, fileno(STDOUT), $s, length $s);

	   Note that Perl supports passing of up to only 14 arguments to your syscall, which in
	   practice should (usually) suffice.

	   Syscall returns whatever value returned by the system call it calls.  If the system
	   call fails, "syscall" returns "-1" and sets $! (errno).  Note that some system calls
	   can legitimately return "-1".  The proper way to handle such calls is to assign "$!=0"
	   before the call, then check the value of $! if "syscall" returns "-1".

	   There's a problem with "syscall(&SYS_pipe)": it returns the file number of the read
	   end of the pipe it creates, but there is no way to retrieve the file number of the
	   other end.  You can avoid this problem by using "pipe" instead.

	   Portability issues: "syscall" in perlport.

       sysopen FILEHANDLE,FILENAME,MODE
       sysopen FILEHANDLE,FILENAME,MODE,PERMS
	   Opens the file whose filename is given by FILENAME, and associates it with FILEHANDLE.
	   If FILEHANDLE is an expression, its value is used as the real filehandle wanted; an
	   undefined scalar will be suitably autovivified.  This function calls the underlying
	   operating system's open(2) function with the parameters FILENAME, MODE, and PERMS.

	   The possible values and flag bits of the MODE parameter are system-dependent; they are
	   available via the standard module "Fcntl".  See the documentation of your operating
	   system's open(2) syscall to see which values and flag bits are available.  You may
	   combine several flags using the "|"-operator.

	   Some of the most common values are "O_RDONLY" for opening the file in read-only mode,
	   "O_WRONLY" for opening the file in write-only mode, and "O_RDWR" for opening the file
	   in read-write mode.

	   For historical reasons, some values work on almost every system supported by Perl: 0
	   means read-only, 1 means write-only, and 2 means read/write.  We know that these
	   values do not work under OS/390 & VM/ESA Unix and on the Macintosh; you probably don't
	   want to use them in new code.

	   If the file named by FILENAME does not exist and the "open" call creates it (typically
	   because MODE includes the "O_CREAT" flag), then the value of PERMS specifies the
	   permissions of the newly created file.  If you omit the PERMS argument to "sysopen",
	   Perl uses the octal value 0666.  These permission values need to be in octal, and are
	   modified by your process's current "umask".

	   In many systems the "O_EXCL" flag is available for opening files in exclusive mode.
	   This is not locking: exclusiveness means here that if the file already exists,
	   sysopen() fails.  "O_EXCL" may not work on network filesystems, and has no effect
	   unless the "O_CREAT" flag is set as well.  Setting "O_CREAT|O_EXCL" prevents the file
	   from being opened if it is a symbolic link.	It does not protect against symbolic
	   links in the file's path.

	   Sometimes you may want to truncate an already-existing file.  This can be done using
	   the "O_TRUNC" flag.	The behavior of "O_TRUNC" with "O_RDONLY" is undefined.

	   You should seldom if ever use 0644 as argument to "sysopen", because that takes away
	   the user's option to have a more permissive umask.  Better to omit it.  See the
	   perlfunc(1) entry on "umask" for more on this.

	   Note that "sysopen" depends on the fdopen() C library function.  On many Unix systems,
	   fdopen() is known to fail when file descriptors exceed a certain value, typically 255.
	   If you need more file descriptors than that, consider rebuilding Perl to use the
	   "sfio" library, or perhaps using the POSIX::open() function.

	   See perlopentut for a kinder, gentler explanation of opening files.

	   Portability issues: "sysopen" in perlport.

       sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
       sysread FILEHANDLE,SCALAR,LENGTH
	   Attempts to read LENGTH bytes of data into variable SCALAR from the specified
	   FILEHANDLE, using the read(2).  It bypasses buffered IO, so mixing this with other
	   kinds of reads, "print", "write", "seek", "tell", or "eof" can cause confusion because
	   the perlio or stdio layers usually buffers data.  Returns the number of bytes actually
	   read, 0 at end of file, or undef if there was an error (in the latter case $! is also
	   set).  SCALAR will be grown or shrunk so that the last byte actually read is the last
	   byte of the scalar after the read.

	   An OFFSET may be specified to place the read data at some place in the string other
	   than the beginning.	A negative OFFSET specifies placement at that many characters
	   counting backwards from the end of the string.  A positive OFFSET greater than the
	   length of SCALAR results in the string being padded to the required size with "\0"
	   bytes before the result of the read is appended.

	   There is no syseof() function, which is ok, since eof() doesn't work well on device
	   files (like ttys) anyway.  Use sysread() and check for a return value for 0 to decide
	   whether you're done.

	   Note that if the filehandle has been marked as ":utf8" Unicode characters are read
	   instead of bytes (the LENGTH, OFFSET, and the return value of sysread() are in Unicode
	   characters).  The ":encoding(...)" layer implicitly introduces the ":utf8" layer.  See
	   "binmode", "open", and the "open" pragma, open.

       sysseek FILEHANDLE,POSITION,WHENCE
	   Sets FILEHANDLE's system position in bytes using lseek(2).  FILEHANDLE may be an
	   expression whose value gives the name of the filehandle.  The values for WHENCE are 0
	   to set the new position to POSITION; 1 to set the it to the current position plus
	   POSITION; and 2 to set it to EOF plus POSITION, typically negative.

	   Note the in bytes: even if the filehandle has been set to operate on characters (for
	   example by using the ":encoding(utf8)" I/O layer), tell() will return byte offsets,
	   not character offsets (because implementing that would render sysseek() unacceptably
	   slow).

	   sysseek() bypasses normal buffered IO, so mixing it with reads other than "sysread"
	   (for example "<>" or read()) "print", "write", "seek", "tell", or "eof" may cause
	   confusion.

	   For WHENCE, you may also use the constants "SEEK_SET", "SEEK_CUR", and "SEEK_END"
	   (start of the file, current position, end of the file) from the Fcntl module.  Use of
	   the constants is also more portable than relying on 0, 1, and 2.  For example to
	   define a "systell" function:

	       use Fcntl 'SEEK_CUR';
	       sub systell { sysseek($_[0], 0, SEEK_CUR) }

	   Returns the new position, or the undefined value on failure.  A position of zero is
	   returned as the string "0 but true"; thus "sysseek" returns true on success and false
	   on failure, yet you can still easily determine the new position.

       system LIST
       system PROGRAM LIST
	   Does exactly the same thing as "exec LIST", except that a fork is done first and the
	   parent process waits for the child process to exit.	Note that argument processing
	   varies depending on the number of arguments.  If there is more than one argument in
	   LIST, or if LIST is an array with more than one value, starts the program given by the
	   first element of the list with arguments given by the rest of the list.  If there is
	   only one scalar argument, the argument is checked for shell metacharacters, and if
	   there are any, the entire argument is passed to the system's command shell for parsing
	   (this is "/bin/sh -c" on Unix platforms, but varies on other platforms).  If there are
	   no shell metacharacters in the argument, it is split into words and passed directly to
	   "execvp", which is more efficient.

	   Beginning with v5.6.0, Perl will attempt to flush all files opened for output before
	   any operation that may do a fork, but this may not be supported on some platforms (see
	   perlport).  To be safe, you may need to set $| ($AUTOFLUSH in English) or call the
	   "autoflush()" method of "IO::Handle" on any open handles.

	   The return value is the exit status of the program as returned by the "wait" call.  To
	   get the actual exit value, shift right by eight (see below).  See also "exec".  This
	   is not what you want to use to capture the output from a command; for that you should
	   use merely backticks or "qx//", as described in "`STRING`" in perlop.  Return value of
	   -1 indicates a failure to start the program or an error of the wait(2) system call
	   (inspect $! for the reason).

	   If you'd like to make "system" (and many other bits of Perl) die on error, have a look
	   at the autodie pragma.

	   Like "exec", "system" allows you to lie to a program about its name if you use the
	   "system PROGRAM LIST" syntax.  Again, see "exec".

	   Since "SIGINT" and "SIGQUIT" are ignored during the execution of "system", if you
	   expect your program to terminate on receipt of these signals you will need to arrange
	   to do so yourself based on the return value.

	       @args = ("command", "arg1", "arg2");
	       system(@args) == 0
		   or die "system @args failed: $?"

	   If you'd like to manually inspect "system"'s failure, you can check all possible
	   failure modes by inspecting $? like this:

	       if ($? == -1) {
		   print "failed to execute: $!\n";
	       }
	       elsif ($? & 127) {
		   printf "child died with signal %d, %s coredump\n",
		       ($? & 127),  ($? & 128) ? 'with' : 'without';
	       }
	       else {
		   printf "child exited with value %d\n", $? >> 8;
	       }

	   Alternatively, you may inspect the value of "${^CHILD_ERROR_NATIVE}" with the "W*()"
	   calls from the POSIX module.

	   When "system"'s arguments are executed indirectly by the shell, results and return
	   codes are subject to its quirks.  See "`STRING`" in perlop and "exec" for details.

	   Since "system" does a "fork" and "wait" it may affect a "SIGCHLD" handler.  See
	   perlipc for details.

	   Portability issues: "system" in perlport.

       syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
       syswrite FILEHANDLE,SCALAR,LENGTH
       syswrite FILEHANDLE,SCALAR
	   Attempts to write LENGTH bytes of data from variable SCALAR to the specified
	   FILEHANDLE, using write(2).	If LENGTH is not specified, writes whole SCALAR.  It
	   bypasses buffered IO, so mixing this with reads (other than sysread()), "print",
	   "write", "seek", "tell", or "eof" may cause confusion because the perlio and stdio
	   layers usually buffer data.	Returns the number of bytes actually written, or "undef"
	   if there was an error (in this case the errno variable $! is also set).  If the LENGTH
	   is greater than the data available in the SCALAR after the OFFSET, only as much data
	   as is available will be written.

	   An OFFSET may be specified to write the data from some part of the string other than
	   the beginning.  A negative OFFSET specifies writing that many characters counting
	   backwards from the end of the string.  If SCALAR is of length zero, you can only use
	   an OFFSET of 0.

	   WARNING: If the filehandle is marked ":utf8", Unicode characters encoded in UTF-8 are
	   written instead of bytes, and the LENGTH, OFFSET, and return value of syswrite() are
	   in (UTF8-encoded Unicode) characters.  The ":encoding(...)" layer implicitly
	   introduces the ":utf8" layer.  Alternately, if the handle is not marked with an
	   encoding but you attempt to write characters with code points over 255, raises an
	   exception.  See "binmode", "open", and the "open" pragma, open.

       tell FILEHANDLE
       tell
	   Returns the current position in bytes for FILEHANDLE, or -1 on error.  FILEHANDLE may
	   be an expression whose value gives the name of the actual filehandle.  If FILEHANDLE
	   is omitted, assumes the file last read.

	   Note the in bytes: even if the filehandle has been set to operate on characters (for
	   example by using the ":encoding(utf8)" open layer), tell() will return byte offsets,
	   not character offsets (because that would render seek() and tell() rather slow).

	   The return value of tell() for the standard streams like the STDIN depends on the
	   operating system: it may return -1 or something else.  tell() on pipes, fifos, and
	   sockets usually returns -1.

	   There is no "systell" function.  Use "sysseek(FH, 0, 1)" for that.

	   Do not use tell() (or other buffered I/O operations) on a filehandle that has been
	   manipulated by sysread(), syswrite(), or sysseek().	Those functions ignore the
	   buffering, while tell() does not.

       telldir DIRHANDLE
	   Returns the current position of the "readdir" routines on DIRHANDLE.  Value may be
	   given to "seekdir" to access a particular location in a directory.  "telldir" has the
	   same caveats about possible directory compaction as the corresponding system library
	   routine.

       tie VARIABLE,CLASSNAME,LIST
	   This function binds a variable to a package class that will provide the implementation
	   for the variable.  VARIABLE is the name of the variable to be enchanted.  CLASSNAME is
	   the name of a class implementing objects of correct type.  Any additional arguments
	   are passed to the "new" method of the class (meaning "TIESCALAR", "TIEHANDLE",
	   "TIEARRAY", or "TIEHASH").  Typically these are arguments such as might be passed to
	   the "dbm_open()" function of C.  The object returned by the "new" method is also
	   returned by the "tie" function, which would be useful if you want to access other
	   methods in CLASSNAME.

	   Note that functions such as "keys" and "values" may return huge lists when used on
	   large objects, like DBM files.  You may prefer to use the "each" function to iterate
	   over such.  Example:

	       # print out history file offsets
	       use NDBM_File;
	       tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
	       while (($key,$val) = each %HIST) {
		   print $key, ' = ', unpack('L',$val), "\n";
	       }
	       untie(%HIST);

	   A class implementing a hash should have the following methods:

	       TIEHASH classname, LIST
	       FETCH this, key
	       STORE this, key, value
	       DELETE this, key
	       CLEAR this
	       EXISTS this, key
	       FIRSTKEY this
	       NEXTKEY this, lastkey
	       SCALAR this
	       DESTROY this
	       UNTIE this

	   A class implementing an ordinary array should have the following methods:

	       TIEARRAY classname, LIST
	       FETCH this, key
	       STORE this, key, value
	       FETCHSIZE this
	       STORESIZE this, count
	       CLEAR this
	       PUSH this, LIST
	       POP this
	       SHIFT this
	       UNSHIFT this, LIST
	       SPLICE this, offset, length, LIST
	       EXTEND this, count
	       DESTROY this
	       UNTIE this

	   A class implementing a filehandle should have the following methods:

	       TIEHANDLE classname, LIST
	       READ this, scalar, length, offset
	       READLINE this
	       GETC this
	       WRITE this, scalar, length, offset
	       PRINT this, LIST
	       PRINTF this, format, LIST
	       BINMODE this
	       EOF this
	       FILENO this
	       SEEK this, position, whence
	       TELL this
	       OPEN this, mode, LIST
	       CLOSE this
	       DESTROY this
	       UNTIE this

	   A class implementing a scalar should have the following methods:

	       TIESCALAR classname, LIST
	       FETCH this,
	       STORE this, value
	       DESTROY this
	       UNTIE this

	   Not all methods indicated above need be implemented.  See perltie, Tie::Hash,
	   Tie::Array, Tie::Scalar, and Tie::Handle.

	   Unlike "dbmopen", the "tie" function will not "use" or "require" a module for you; you
	   need to do that explicitly yourself.  See DB_File or the Config module for interesting
	   "tie" implementations.

	   For further details see perltie, "tied VARIABLE".

       tied VARIABLE
	   Returns a reference to the object underlying VARIABLE (the same value that was
	   originally returned by the "tie" call that bound the variable to a package.)  Returns
	   the undefined value if VARIABLE isn't tied to a package.

       time
	   Returns the number of non-leap seconds since whatever time the system considers to be
	   the epoch, suitable for feeding to "gmtime" and "localtime".  On most systems the
	   epoch is 00:00:00 UTC, January 1, 1970; a prominent exception being Mac OS Classic
	   which uses 00:00:00, January 1, 1904 in the current local time zone for its epoch.

	   For measuring time in better granularity than one second, use the Time::HiRes module
	   from Perl 5.8 onwards (or from CPAN before then), or, if you have gettimeofday(2), you
	   may be able to use the "syscall" interface of Perl.	See perlfaq8 for details.

	   For date and time processing look at the many related modules on CPAN.  For a
	   comprehensive date and time representation look at the DateTime module.

       times
	   Returns a four-element list giving the user and system times in seconds for this
	   process and any exited children of this process.

	       ($user,$system,$cuser,$csystem) = times;

	   In scalar context, "times" returns $user.

	   Children's times are only included for terminated children.

	   Portability issues: "times" in perlport.

       tr///
	   The transliteration operator.  Same as "y///".  See "Quote and Quote-like Operators"
	   in perlop.

       truncate FILEHANDLE,LENGTH
       truncate EXPR,LENGTH
	   Truncates the file opened on FILEHANDLE, or named by EXPR, to the specified length.
	   Raises an exception if truncate isn't implemented on your system.  Returns true if
	   successful, "undef" on error.

	   The behavior is undefined if LENGTH is greater than the length of the file.

	   The position in the file of FILEHANDLE is left unchanged.  You may want to call seek
	   before writing to the file.

	   Portability issues: "truncate" in perlport.

       uc EXPR
       uc  Returns an uppercased version of EXPR.  This is the internal function implementing the
	   "\U" escape in double-quoted strings.  It does not attempt to do titlecase mapping on
	   initial letters.  See "ucfirst" for that.

	   If EXPR is omitted, uses $_.

	   This function behaves the same way under various pragma, such as in a locale, as "lc"
	   does.

       ucfirst EXPR
       ucfirst
	   Returns the value of EXPR with the first character in uppercase (titlecase in
	   Unicode).  This is the internal function implementing the "\u" escape in double-quoted
	   strings.

	   If EXPR is omitted, uses $_.

	   This function behaves the same way under various pragma, such as in a locale, as "lc"
	   does.

       umask EXPR
       umask
	   Sets the umask for the process to EXPR and returns the previous value.  If EXPR is
	   omitted, merely returns the current umask.

	   The Unix permission "rwxr-x---" is represented as three sets of three bits, or three
	   octal digits: 0750 (the leading 0 indicates octal and isn't one of the digits).  The
	   "umask" value is such a number representing disabled permissions bits.  The permission
	   (or "mode") values you pass "mkdir" or "sysopen" are modified by your umask, so even
	   if you tell "sysopen" to create a file with permissions 0777, if your umask is 0022,
	   then the file will actually be created with permissions 0755.  If your "umask" were
	   0027 (group can't write; others can't read, write, or execute), then passing "sysopen"
	   0666 would create a file with mode 0640 (because "0666 &~ 027" is 0640).

	   Here's some advice: supply a creation mode of 0666 for regular files (in "sysopen")
	   and one of 0777 for directories (in "mkdir") and executable files.  This gives users
	   the freedom of choice: if they want protected files, they might choose process umasks
	   of 022, 027, or even the particularly antisocial mask of 077.  Programs should rarely
	   if ever make policy decisions better left to the user.  The exception to this is when
	   writing files that should be kept private: mail files, web browser cookies, .rhosts
	   files, and so on.

	   If umask(2) is not implemented on your system and you are trying to restrict access
	   for yourself (i.e., "(EXPR & 0700) > 0"), raises an exception.  If umask(2) is not
	   implemented and you are not trying to restrict access for yourself, returns "undef".

	   Remember that a umask is a number, usually given in octal; it is not a string of octal
	   digits.  See also "oct", if all you have is a string.

	   Portability issues: "umask" in perlport.

       undef EXPR
       undef
	   Undefines the value of EXPR, which must be an lvalue.  Use only on a scalar value, an
	   array (using "@"), a hash (using "%"), a subroutine (using "&"), or a typeglob (using
	   "*").  Saying "undef $hash{$key}" will probably not do what you expect on most
	   predefined variables or DBM list values, so don't do that; see "delete".  Always
	   returns the undefined value.  You can omit the EXPR, in which case nothing is
	   undefined, but you still get an undefined value that you could, for instance, return
	   from a subroutine, assign to a variable, or pass as a parameter.  Examples:

	       undef $foo;
	       undef $bar{'blurfl'};	  # Compare to: delete $bar{'blurfl'};
	       undef @ary;
	       undef %hash;
	       undef &mysub;
	       undef *xyz;	 # destroys $xyz, @xyz, %xyz, &xyz, etc.
	       return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
	       select undef, undef, undef, 0.25;
	       ($a, $b, undef, $c) = &foo;	 # Ignore third value returned

	   Note that this is a unary operator, not a list operator.

       unlink LIST
       unlink
	   Deletes a list of files.  On success, it returns the number of files it successfully
	   deleted.  On failure, it returns false and sets $!  (errno):

	       my $unlinked = unlink 'a', 'b', 'c';
	       unlink @goners;
	       unlink glob "*.bak";

	   On error, "unlink" will not tell you which files it could not remove.  If you want to
	   know which files you could not remove, try them one at a time:

		foreach my $file ( @goners ) {
		    unlink $file or warn "Could not unlink $file: $!";
		}

	   Note: "unlink" will not attempt to delete directories unless you are superuser and the
	   -U flag is supplied to Perl.  Even if these conditions are met, be warned that
	   unlinking a directory can inflict damage on your filesystem.  Finally, using "unlink"
	   on directories is not supported on many operating systems.  Use "rmdir" instead.

	   If LIST is omitted, "unlink" uses $_.

       unpack TEMPLATE,EXPR
       unpack TEMPLATE
	   "unpack" does the reverse of "pack": it takes a string and expands it out into a list
	   of values.  (In scalar context, it returns merely the first value produced.)

	   If EXPR is omitted, unpacks the $_ string.  See perlpacktut for an introduction to
	   this function.

	   The string is broken into chunks described by the TEMPLATE.	Each chunk is converted
	   separately to a value.  Typically, either the string is a result of "pack", or the
	   characters of the string represent a C structure of some kind.

	   The TEMPLATE has the same format as in the "pack" function.	Here's a subroutine that
	   does substring:

	       sub substr {
		   my($what,$where,$howmuch) = @_;
		   unpack("x$where a$howmuch", $what);
	       }

	   and then there's

	       sub ordinal { unpack("W",$_[0]); } # same as ord()

	   In addition to fields allowed in pack(), you may prefix a field with a %<number> to
	   indicate that you want a <number>-bit checksum of the items instead of the items
	   themselves.	Default is a 16-bit checksum.  Checksum is calculated by summing numeric
	   values of expanded values (for string fields the sum of "ord($char)" is taken; for bit
	   fields the sum of zeroes and ones).

	   For example, the following computes the same number as the System V sum program:

	       $checksum = do {
		   local $/;  # slurp!
		   unpack("%32W*",<>) % 65535;
	       };

	   The following efficiently counts the number of set bits in a bit vector:

	       $setbits = unpack("%32b*", $selectmask);

	   The "p" and "P" formats should be used with care.  Since Perl has no way of checking
	   whether the value passed to "unpack()" corresponds to a valid memory location, passing
	   a pointer value that's not known to be valid is likely to have disastrous
	   consequences.

	   If there are more pack codes or if the repeat count of a field or a group is larger
	   than what the remainder of the input string allows, the result is not well defined:
	   the repeat count may be decreased, or "unpack()" may produce empty strings or zeros,
	   or it may raise an exception.  If the input string is longer than one described by the
	   TEMPLATE, the remainder of that input string is ignored.

	   See "pack" for more examples and notes.

       unshift ARRAY,LIST
       unshift EXPR,LIST
	   Does the opposite of a "shift".  Or the opposite of a "push", depending on how you
	   look at it.	Prepends list to the front of the array and returns the new number of
	   elements in the array.

	       unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;

	   Note the LIST is prepended whole, not one element at a time, so the prepended elements
	   stay in the same order.  Use "reverse" to do the reverse.

	   Starting with Perl 5.14, "unshift" can take a scalar EXPR, which must hold a reference
	   to an unblessed array.  The argument will be dereferenced automatically.  This aspect
	   of "unshift" is considered highly experimental.  The exact behaviour may change in a
	   future version of Perl.

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.014;  # so push/pop/etc work on scalars (experimental)

       untie VARIABLE
	   Breaks the binding between a variable and a package.  (See tie.)  Has no effect if the
	   variable is not tied.

       use Module VERSION LIST
       use Module VERSION
       use Module LIST
       use Module
       use VERSION
	   Imports some semantics into the current package from the named module, generally by
	   aliasing certain subroutine or variable names into your package.  It is exactly
	   equivalent to

	       BEGIN { require Module; Module->import( LIST ); }

	   except that Module must be a bareword.  The importation can be made conditional; see
	   if.

	   In the peculiar "use VERSION" form, VERSION may be either a positive decimal fraction
	   such as 5.006, which will be compared to $], or a v-string of the form v5.6.1, which
	   will be compared to $^V (aka $PERL_VERSION).  An exception is raised if VERSION is
	   greater than the version of the current Perl interpreter; Perl will not attempt to
	   parse the rest of the file.	Compare with "require", which can do a similar check at
	   run time.  Symmetrically, "no VERSION" allows you to specify that you want a version
	   of Perl older than the specified one.

	   Specifying VERSION as a literal of the form v5.6.1 should generally be avoided,
	   because it leads to misleading error messages under earlier versions of Perl (that is,
	   prior to 5.6.0) that do not support this syntax.  The equivalent numeric version
	   should be used instead.

	       use v5.6.1;     # compile time version check
	       use 5.6.1;      # ditto
	       use 5.006_001;  # ditto; preferred for backwards compatibility

	   This is often useful if you need to check the current Perl version before "use"ing
	   library modules that won't work with older versions of Perl.  (We try not to do this
	   more than we have to.)

	   "use VERSION" also enables all features available in the requested version as defined
	   by the "feature" pragma, disabling any features not in the requested version's feature
	   bundle.  See feature.  Similarly, if the specified Perl version is greater than or
	   equal to 5.11.0, strictures are enabled lexically as with "use strict".  Any explicit
	   use of "use strict" or "no strict" overrides "use VERSION", even if it comes before
	   it.	In both cases, the feature.pm and strict.pm files are not actually loaded.

	   The "BEGIN" forces the "require" and "import" to happen at compile time.  The
	   "require" makes sure the module is loaded into memory if it hasn't been yet.  The
	   "import" is not a builtin; it's just an ordinary static method call into the "Module"
	   package to tell the module to import the list of features back into the current
	   package.  The module can implement its "import" method any way it likes, though most
	   modules just choose to derive their "import" method via inheritance from the
	   "Exporter" class that is defined in the "Exporter" module.  See Exporter.  If no
	   "import" method can be found then the call is skipped, even if there is an AUTOLOAD
	   method.

	   If you do not want to call the package's "import" method (for instance, to stop your
	   namespace from being altered), explicitly supply the empty list:

	       use Module ();

	   That is exactly equivalent to

	       BEGIN { require Module }

	   If the VERSION argument is present between Module and LIST, then the "use" will call
	   the VERSION method in class Module with the given version as an argument.  The default
	   VERSION method, inherited from the UNIVERSAL class, croaks if the given version is
	   larger than the value of the variable $Module::VERSION.

	   Again, there is a distinction between omitting LIST ("import" called with no
	   arguments) and an explicit empty LIST "()" ("import" not called).  Note that there is
	   no comma after VERSION!

	   Because this is a wide-open interface, pragmas (compiler directives) are also
	   implemented this way.  Currently implemented pragmas are:

	       use constant;
	       use diagnostics;
	       use integer;
	       use sigtrap  qw(SEGV BUS);
	       use strict   qw(subs vars refs);
	       use subs     qw(afunc blurfl);
	       use warnings qw(all);
	       use sort     qw(stable _quicksort _mergesort);

	   Some of these pseudo-modules import semantics into the current block scope (like
	   "strict" or "integer", unlike ordinary modules, which import symbols into the current
	   package (which are effective through the end of the file).

	   Because "use" takes effect at compile time, it doesn't respect the ordinary flow
	   control of the code being compiled.	In particular, putting a "use" inside the false
	   branch of a conditional doesn't prevent it from being processed.  If a module or
	   pragma only needs to be loaded conditionally, this can be done using the if pragma:

	       use if $] < 5.008, "utf8";
	       use if WANT_WARNINGS, warnings => qw(all);

	   There's a corresponding "no" declaration that unimports meanings imported by "use",
	   i.e., it calls "unimport Module LIST" instead of "import".  It behaves just as
	   "import" does with VERSION, an omitted or empty LIST, or no unimport method being
	   found.

	       no integer;
	       no strict 'refs';
	       no warnings;

	   Care should be taken when using the "no VERSION" form of "no".  It is only meant to be
	   used to assert that the running Perl is of a earlier version than its argument and not
	   to undo the feature-enabling side effects of "use VERSION".

	   See perlmodlib for a list of standard modules and pragmas.  See perlrun for the "-M"
	   and "-m" command-line options to Perl that give "use" functionality from the command-
	   line.

       utime LIST
	   Changes the access and modification times on each file of a list of files.  The first
	   two elements of the list must be the NUMERIC access and modification times, in that
	   order.  Returns the number of files successfully changed.  The inode change time of
	   each file is set to the current time.  For example, this code has the same effect as
	   the Unix touch(1) command when the files already exist and belong to the user running
	   the program:

	       #!/usr/bin/perl
	       $atime = $mtime = time;
	       utime $atime, $mtime, @ARGV;

	   Since Perl 5.7.2, if the first two elements of the list are "undef", the utime(2)
	   syscall from your C library is called with a null second argument.  On most systems,
	   this will set the file's access and modification times to the current time (i.e.,
	   equivalent to the example above) and will work even on files you don't own provided
	   you have write permission:

	       for $file (@ARGV) {
		   utime(undef, undef, $file)
		       || warn "couldn't touch $file: $!";
	       }

	   Under NFS this will use the time of the NFS server, not the time of the local machine.
	   If there is a time synchronization problem, the NFS server and local machine will have
	   different times.  The Unix touch(1) command will in fact normally use this form
	   instead of the one shown in the first example.

	   Passing only one of the first two elements as "undef" is equivalent to passing a 0 and
	   will not have the effect described when both are "undef".  This also triggers an
	   uninitialized warning.

	   On systems that support futimes(2), you may pass filehandles among the files.  On
	   systems that don't support futimes(2), passing filehandles raises an exception.
	   Filehandles must be passed as globs or glob references to be recognized; barewords are
	   considered filenames.

	   Portability issues: "utime" in perlport.

       values HASH
       values ARRAY
       values EXPR
	   In list context, returns a list consisting of all the values of the named hash.  In
	   Perl 5.12 or later only, will also return a list of the values of an array; prior to
	   that release, attempting to use an array argument will produce a syntax error.  In
	   scalar context, returns the number of values.

	   When called on a hash, the values are returned in an apparently random order.  The
	   actual random order is subject to change in future versions of Perl, but it is
	   guaranteed to be the same order as either the "keys" or "each" function would produce
	   on the same (unmodified) hash.  Since Perl 5.8.1 the ordering is different even
	   between different runs of Perl for security reasons (see "Algorithmic Complexity
	   Attacks" in perlsec).

	   As a side effect, calling values() resets the HASH or ARRAY's internal iterator, see
	   "each".  (In particular, calling values() in void context resets the iterator with no
	   other overhead.  Apart from resetting the iterator, "values @array" in list context is
	   the same as plain @array.  (We recommend that you use void context "keys @array" for
	   this, but reasoned that taking "values @array" out would require more documentation
	   than leaving it in.)

	   Note that the values are not copied, which means modifying them will modify the
	   contents of the hash:

	       for (values %hash)      { s/foo/bar/g }	 # modifies %hash values
	       for (@hash{keys %hash}) { s/foo/bar/g }	 # same

	   Starting with Perl 5.14, "values" can take a scalar EXPR, which must hold a reference
	   to an unblessed hash or array.  The argument will be dereferenced automatically.  This
	   aspect of "values" is considered highly experimental.  The exact behaviour may change
	   in a future version of Perl.

	       for (values $hashref) { ... }
	       for (values $obj->get_arrayref) { ... }

	   To avoid confusing would-be users of your code who are running earlier versions of
	   Perl with mysterious syntax errors, put this sort of thing at the top of your file to
	   signal that your code will work only on Perls of a recent vintage:

	       use 5.012;  # so keys/values/each work on arrays
	       use 5.014;  # so keys/values/each work on scalars (experimental)

	   See also "keys", "each", and "sort".

       vec EXPR,OFFSET,BITS
	   Treats the string in EXPR as a bit vector made up of elements of width BITS and
	   returns the value of the element specified by OFFSET as an unsigned integer.  BITS
	   therefore specifies the number of bits that are reserved for each element in the bit
	   vector.  This must be a power of two from 1 to 32 (or 64, if your platform supports
	   that).

	   If BITS is 8, "elements" coincide with bytes of the input string.

	   If BITS is 16 or more, bytes of the input string are grouped into chunks of size
	   BITS/8, and each group is converted to a number as with pack()/unpack() with big-
	   endian formats "n"/"N" (and analogously for BITS==64).  See "pack" for details.

	   If bits is 4 or less, the string is broken into bytes, then the bits of each byte are
	   broken into 8/BITS groups.  Bits of a byte are numbered in a little-endian-ish way, as
	   in 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80.  For example, breaking the single
	   input byte "chr(0x36)" into two groups gives a list "(0x6, 0x3)"; breaking it into 4
	   groups gives "(0x2, 0x1, 0x3, 0x0)".

	   "vec" may also be assigned to, in which case parentheses are needed to give the
	   expression the correct precedence as in

	       vec($image, $max_x * $x + $y, 8) = 3;

	   If the selected element is outside the string, the value 0 is returned.  If an element
	   off the end of the string is written to, Perl will first extend the string with
	   sufficiently many zero bytes.   It is an error to try to write off the beginning of
	   the string (i.e., negative OFFSET).

	   If the string happens to be encoded as UTF-8 internally (and thus has the UTF8 flag
	   set), this is ignored by "vec", and it operates on the internal byte string, not the
	   conceptual character string, even if you only have characters with values less than
	   256.

	   Strings created with "vec" can also be manipulated with the logical operators "|",
	   "&", "^", and "~".  These operators will assume a bit vector operation is desired when
	   both operands are strings.  See "Bitwise String Operators" in perlop.

	   The following code will build up an ASCII string saying 'PerlPerlPerl'.  The comments
	   show the string after each step.  Note that this code works in the same way on big-
	   endian or little-endian machines.

	       my $foo = '';
	       vec($foo,  0, 32) = 0x5065726C; # 'Perl'

	       # $foo eq "Perl" eq "\x50\x65\x72\x6C", 32 bits
	       print vec($foo, 0, 8);  # prints 80 == 0x50 == ord('P')

	       vec($foo,  2, 16) = 0x5065; # 'PerlPe'
	       vec($foo,  3, 16) = 0x726C; # 'PerlPerl'
	       vec($foo,  8,  8) = 0x50;   # 'PerlPerlP'
	       vec($foo,  9,  8) = 0x65;   # 'PerlPerlPe'
	       vec($foo, 20,  4) = 2;	   # 'PerlPerlPe'   . "\x02"
	       vec($foo, 21,  4) = 7;	   # 'PerlPerlPer'
					      # 'r' is "\x72"
	       vec($foo, 45,  2) = 3;	   # 'PerlPerlPer'  . "\x0c"
	       vec($foo, 93,  1) = 1;	   # 'PerlPerlPer'  . "\x2c"
	       vec($foo, 94,  1) = 1;	   # 'PerlPerlPerl'
					      # 'l' is "\x6c"

	   To transform a bit vector into a string or list of 0's and 1's, use these:

	       $bits = unpack("b*", $vector);
	       @bits = split(//, unpack("b*", $vector));

	   If you know the exact length in bits, it can be used in place of the "*".

	   Here is an example to illustrate how the bits actually fall in place:

	       #!/usr/bin/perl -wl

	       print <<'EOT';
						 0	   1	     2	       3
				  unpack("V",$_) 01234567890123456789012345678901
	       ------------------------------------------------------------------
	       EOT

	       for $w (0..3) {
		   $width = 2**$w;
		   for ($shift=0; $shift < $width; ++$shift) {
		       for ($off=0; $off < 32/$width; ++$off) {
			   $str = pack("B*", "0"x32);
			   $bits = (1<<$shift);
			   vec($str, $off, $width) = $bits;
			   $res = unpack("b*",$str);
			   $val = unpack("V", $str);
			   write;
		       }
		   }
	       }

	       format STDOUT =
	       vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
	       $off, $width, $bits, $val, $res
	       .
	       __END__

	   Regardless of the machine architecture on which it runs, the example above should
	   print the following table:

						 0	   1	     2	       3
				  unpack("V",$_) 01234567890123456789012345678901
	       ------------------------------------------------------------------
	       vec($_, 0, 1) = 1   ==	       1 10000000000000000000000000000000
	       vec($_, 1, 1) = 1   ==	       2 01000000000000000000000000000000
	       vec($_, 2, 1) = 1   ==	       4 00100000000000000000000000000000
	       vec($_, 3, 1) = 1   ==	       8 00010000000000000000000000000000
	       vec($_, 4, 1) = 1   ==	      16 00001000000000000000000000000000
	       vec($_, 5, 1) = 1   ==	      32 00000100000000000000000000000000
	       vec($_, 6, 1) = 1   ==	      64 00000010000000000000000000000000
	       vec($_, 7, 1) = 1   ==	     128 00000001000000000000000000000000
	       vec($_, 8, 1) = 1   ==	     256 00000000100000000000000000000000
	       vec($_, 9, 1) = 1   ==	     512 00000000010000000000000000000000
	       vec($_,10, 1) = 1   ==	    1024 00000000001000000000000000000000
	       vec($_,11, 1) = 1   ==	    2048 00000000000100000000000000000000
	       vec($_,12, 1) = 1   ==	    4096 00000000000010000000000000000000
	       vec($_,13, 1) = 1   ==	    8192 00000000000001000000000000000000
	       vec($_,14, 1) = 1   ==	   16384 00000000000000100000000000000000
	       vec($_,15, 1) = 1   ==	   32768 00000000000000010000000000000000
	       vec($_,16, 1) = 1   ==	   65536 00000000000000001000000000000000
	       vec($_,17, 1) = 1   ==	  131072 00000000000000000100000000000000
	       vec($_,18, 1) = 1   ==	  262144 00000000000000000010000000000000
	       vec($_,19, 1) = 1   ==	  524288 00000000000000000001000000000000
	       vec($_,20, 1) = 1   ==	 1048576 00000000000000000000100000000000
	       vec($_,21, 1) = 1   ==	 2097152 00000000000000000000010000000000
	       vec($_,22, 1) = 1   ==	 4194304 00000000000000000000001000000000
	       vec($_,23, 1) = 1   ==	 8388608 00000000000000000000000100000000
	       vec($_,24, 1) = 1   ==	16777216 00000000000000000000000010000000
	       vec($_,25, 1) = 1   ==	33554432 00000000000000000000000001000000
	       vec($_,26, 1) = 1   ==	67108864 00000000000000000000000000100000
	       vec($_,27, 1) = 1   ==  134217728 00000000000000000000000000010000
	       vec($_,28, 1) = 1   ==  268435456 00000000000000000000000000001000
	       vec($_,29, 1) = 1   ==  536870912 00000000000000000000000000000100
	       vec($_,30, 1) = 1   == 1073741824 00000000000000000000000000000010
	       vec($_,31, 1) = 1   == 2147483648 00000000000000000000000000000001
	       vec($_, 0, 2) = 1   ==	       1 10000000000000000000000000000000
	       vec($_, 1, 2) = 1   ==	       4 00100000000000000000000000000000
	       vec($_, 2, 2) = 1   ==	      16 00001000000000000000000000000000
	       vec($_, 3, 2) = 1   ==	      64 00000010000000000000000000000000
	       vec($_, 4, 2) = 1   ==	     256 00000000100000000000000000000000
	       vec($_, 5, 2) = 1   ==	    1024 00000000001000000000000000000000
	       vec($_, 6, 2) = 1   ==	    4096 00000000000010000000000000000000
	       vec($_, 7, 2) = 1   ==	   16384 00000000000000100000000000000000
	       vec($_, 8, 2) = 1   ==	   65536 00000000000000001000000000000000
	       vec($_, 9, 2) = 1   ==	  262144 00000000000000000010000000000000
	       vec($_,10, 2) = 1   ==	 1048576 00000000000000000000100000000000
	       vec($_,11, 2) = 1   ==	 4194304 00000000000000000000001000000000
	       vec($_,12, 2) = 1   ==	16777216 00000000000000000000000010000000
	       vec($_,13, 2) = 1   ==	67108864 00000000000000000000000000100000
	       vec($_,14, 2) = 1   ==  268435456 00000000000000000000000000001000
	       vec($_,15, 2) = 1   == 1073741824 00000000000000000000000000000010
	       vec($_, 0, 2) = 2   ==	       2 01000000000000000000000000000000
	       vec($_, 1, 2) = 2   ==	       8 00010000000000000000000000000000
	       vec($_, 2, 2) = 2   ==	      32 00000100000000000000000000000000
	       vec($_, 3, 2) = 2   ==	     128 00000001000000000000000000000000
	       vec($_, 4, 2) = 2   ==	     512 00000000010000000000000000000000
	       vec($_, 5, 2) = 2   ==	    2048 00000000000100000000000000000000
	       vec($_, 6, 2) = 2   ==	    8192 00000000000001000000000000000000
	       vec($_, 7, 2) = 2   ==	   32768 00000000000000010000000000000000
	       vec($_, 8, 2) = 2   ==	  131072 00000000000000000100000000000000
	       vec($_, 9, 2) = 2   ==	  524288 00000000000000000001000000000000
	       vec($_,10, 2) = 2   ==	 2097152 00000000000000000000010000000000
	       vec($_,11, 2) = 2   ==	 8388608 00000000000000000000000100000000
	       vec($_,12, 2) = 2   ==	33554432 00000000000000000000000001000000
	       vec($_,13, 2) = 2   ==  134217728 00000000000000000000000000010000
	       vec($_,14, 2) = 2   ==  536870912 00000000000000000000000000000100
	       vec($_,15, 2) = 2   == 2147483648 00000000000000000000000000000001
	       vec($_, 0, 4) = 1   ==	       1 10000000000000000000000000000000
	       vec($_, 1, 4) = 1   ==	      16 00001000000000000000000000000000
	       vec($_, 2, 4) = 1   ==	     256 00000000100000000000000000000000
	       vec($_, 3, 4) = 1   ==	    4096 00000000000010000000000000000000
	       vec($_, 4, 4) = 1   ==	   65536 00000000000000001000000000000000
	       vec($_, 5, 4) = 1   ==	 1048576 00000000000000000000100000000000
	       vec($_, 6, 4) = 1   ==	16777216 00000000000000000000000010000000
	       vec($_, 7, 4) = 1   ==  268435456 00000000000000000000000000001000
	       vec($_, 0, 4) = 2   ==	       2 01000000000000000000000000000000
	       vec($_, 1, 4) = 2   ==	      32 00000100000000000000000000000000
	       vec($_, 2, 4) = 2   ==	     512 00000000010000000000000000000000
	       vec($_, 3, 4) = 2   ==	    8192 00000000000001000000000000000000
	       vec($_, 4, 4) = 2   ==	  131072 00000000000000000100000000000000
	       vec($_, 5, 4) = 2   ==	 2097152 00000000000000000000010000000000
	       vec($_, 6, 4) = 2   ==	33554432 00000000000000000000000001000000
	       vec($_, 7, 4) = 2   ==  536870912 00000000000000000000000000000100
	       vec($_, 0, 4) = 4   ==	       4 00100000000000000000000000000000
	       vec($_, 1, 4) = 4   ==	      64 00000010000000000000000000000000
	       vec($_, 2, 4) = 4   ==	    1024 00000000001000000000000000000000
	       vec($_, 3, 4) = 4   ==	   16384 00000000000000100000000000000000
	       vec($_, 4, 4) = 4   ==	  262144 00000000000000000010000000000000
	       vec($_, 5, 4) = 4   ==	 4194304 00000000000000000000001000000000
	       vec($_, 6, 4) = 4   ==	67108864 00000000000000000000000000100000
	       vec($_, 7, 4) = 4   == 1073741824 00000000000000000000000000000010
	       vec($_, 0, 4) = 8   ==	       8 00010000000000000000000000000000
	       vec($_, 1, 4) = 8   ==	     128 00000001000000000000000000000000
	       vec($_, 2, 4) = 8   ==	    2048 00000000000100000000000000000000
	       vec($_, 3, 4) = 8   ==	   32768 00000000000000010000000000000000
	       vec($_, 4, 4) = 8   ==	  524288 00000000000000000001000000000000
	       vec($_, 5, 4) = 8   ==	 8388608 00000000000000000000000100000000
	       vec($_, 6, 4) = 8   ==  134217728 00000000000000000000000000010000
	       vec($_, 7, 4) = 8   == 2147483648 00000000000000000000000000000001
	       vec($_, 0, 8) = 1   ==	       1 10000000000000000000000000000000
	       vec($_, 1, 8) = 1   ==	     256 00000000100000000000000000000000
	       vec($_, 2, 8) = 1   ==	   65536 00000000000000001000000000000000
	       vec($_, 3, 8) = 1   ==	16777216 00000000000000000000000010000000
	       vec($_, 0, 8) = 2   ==	       2 01000000000000000000000000000000
	       vec($_, 1, 8) = 2   ==	     512 00000000010000000000000000000000
	       vec($_, 2, 8) = 2   ==	  131072 00000000000000000100000000000000
	       vec($_, 3, 8) = 2   ==	33554432 00000000000000000000000001000000
	       vec($_, 0, 8) = 4   ==	       4 00100000000000000000000000000000
	       vec($_, 1, 8) = 4   ==	    1024 00000000001000000000000000000000
	       vec($_, 2, 8) = 4   ==	  262144 00000000000000000010000000000000
	       vec($_, 3, 8) = 4   ==	67108864 00000000000000000000000000100000
	       vec($_, 0, 8) = 8   ==	       8 00010000000000000000000000000000
	       vec($_, 1, 8) = 8   ==	    2048 00000000000100000000000000000000
	       vec($_, 2, 8) = 8   ==	  524288 00000000000000000001000000000000
	       vec($_, 3, 8) = 8   ==  134217728 00000000000000000000000000010000
	       vec($_, 0, 8) = 16  ==	      16 00001000000000000000000000000000
	       vec($_, 1, 8) = 16  ==	    4096 00000000000010000000000000000000
	       vec($_, 2, 8) = 16  ==	 1048576 00000000000000000000100000000000
	       vec($_, 3, 8) = 16  ==  268435456 00000000000000000000000000001000
	       vec($_, 0, 8) = 32  ==	      32 00000100000000000000000000000000
	       vec($_, 1, 8) = 32  ==	    8192 00000000000001000000000000000000
	       vec($_, 2, 8) = 32  ==	 2097152 00000000000000000000010000000000
	       vec($_, 3, 8) = 32  ==  536870912 00000000000000000000000000000100
	       vec($_, 0, 8) = 64  ==	      64 00000010000000000000000000000000
	       vec($_, 1, 8) = 64  ==	   16384 00000000000000100000000000000000
	       vec($_, 2, 8) = 64  ==	 4194304 00000000000000000000001000000000
	       vec($_, 3, 8) = 64  == 1073741824 00000000000000000000000000000010
	       vec($_, 0, 8) = 128 ==	     128 00000001000000000000000000000000
	       vec($_, 1, 8) = 128 ==	   32768 00000000000000010000000000000000
	       vec($_, 2, 8) = 128 ==	 8388608 00000000000000000000000100000000
	       vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001

       wait
	   Behaves like wait(2) on your system: it waits for a child process to terminate and
	   returns the pid of the deceased process, or "-1" if there are no child processes.  The
	   status is returned in $?  and "${^CHILD_ERROR_NATIVE}".  Note that a return value of
	   "-1" could mean that child processes are being automatically reaped, as described in
	   perlipc.

	   If you use wait in your handler for $SIG{CHLD} it may accidentally for the child
	   created by qx() or system().  See perlipc for details.

	   Portability issues: "wait" in perlport.

       waitpid PID,FLAGS
	   Waits for a particular child process to terminate and returns the pid of the deceased
	   process, or "-1" if there is no such child process.	On some systems, a value of 0
	   indicates that there are processes still running.  The status is returned in $? and
	   "${^CHILD_ERROR_NATIVE}".  If you say

	       use POSIX ":sys_wait_h";
	       #...
	       do {
		   $kid = waitpid(-1, WNOHANG);
	       } while $kid > 0;

	   then you can do a non-blocking wait for all pending zombie processes.  Non-blocking
	   wait is available on machines supporting either the waitpid(2) or wait4(2) syscalls.
	   However, waiting for a particular pid with FLAGS of 0 is implemented everywhere.
	   (Perl emulates the system call by remembering the status values of processes that have
	   exited but have not been harvested by the Perl script yet.)

	   Note that on some systems, a return value of "-1" could mean that child processes are
	   being automatically reaped.	See perlipc for details, and for other examples.

	   Portability issues: "waitpid" in perlport.

       wantarray
	   Returns true if the context of the currently executing subroutine or "eval" is looking
	   for a list value.  Returns false if the context is looking for a scalar.  Returns the
	   undefined value if the context is looking for no value (void context).

	       return unless defined wantarray; # don't bother doing more
	       my @a = complex_calculation();
	       return wantarray ? @a : "@a";

	   "wantarray()"'s result is unspecified in the top level of a file, in a "BEGIN",
	   "UNITCHECK", "CHECK", "INIT" or "END" block, or in a "DESTROY" method.

	   This function should have been named wantlist() instead.

       warn LIST
	   Prints the value of LIST to STDERR.	If the last element of LIST does not end in a
	   newline, it appends the same file/line number text as "die" does.

	   If the output is empty and $@ already contains a value (typically from a previous
	   eval) that value is used after appending "\t...caught" to $@.  This is useful for
	   staying almost, but not entirely similar to "die".

	   If $@ is empty then the string "Warning: Something's wrong" is used.

	   No message is printed if there is a $SIG{__WARN__} handler installed.  It is the
	   handler's responsibility to deal with the message as it sees fit (like, for instance,
	   converting it into a "die").  Most handlers must therefore arrange to actually display
	   the warnings that they are not prepared to deal with, by calling "warn" again in the
	   handler.  Note that this is quite safe and will not produce an endless loop, since
	   "__WARN__" hooks are not called from inside one.

	   You will find this behavior is slightly different from that of $SIG{__DIE__} handlers
	   (which don't suppress the error text, but can instead call "die" again to change it).

	   Using a "__WARN__" handler provides a powerful way to silence all warnings (even the
	   so-called mandatory ones).  An example:

	       # wipe out *all* compile-time warnings
	       BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } }
	       my $foo = 10;
	       my $foo = 20;	      # no warning about duplicate my $foo,
				      # but hey, you asked for it!
	       # no compile-time or run-time warnings before here
	       $DOWARN = 1;

	       # run-time warnings enabled after here
	       warn "\$foo is alive and $foo!";     # does show up

	   See perlvar for details on setting %SIG entries and for more examples.  See the Carp
	   module for other kinds of warnings using its carp() and cluck() functions.

       write FILEHANDLE
       write EXPR
       write
	   Writes a formatted record (possibly multi-line) to the specified FILEHANDLE, using the
	   format associated with that file.  By default the format for a file is the one having
	   the same name as the filehandle, but the format for the current output channel (see
	   the "select" function) may be set explicitly by assigning the name of the format to
	   the $~ variable.

	   Top of form processing is handled automatically:  if there is insufficient room on the
	   current page for the formatted record, the page is advanced by writing a form feed, a
	   special top-of-page format is used to format the new page header before the record is
	   written.  By default, the top-of-page format is the name of the filehandle with "_TOP"
	   appended.  This would be a problem with autovivified filehandles, but it may be
	   dynamically set to the format of your choice by assigning the name to the $^ variable
	   while that filehandle is selected.  The number of lines remaining on the current page
	   is in variable "$-", which can be set to 0 to force a new page.

	   If FILEHANDLE is unspecified, output goes to the current default output channel, which
	   starts out as STDOUT but may be changed by the "select" operator.  If the FILEHANDLE
	   is an EXPR, then the expression is evaluated and the resulting string is used to look
	   up the name of the FILEHANDLE at run time.  For more on formats, see perlform.

	   Note that write is not the opposite of "read".  Unfortunately.

       y///
	   The transliteration operator.  Same as "tr///".  See "Quote and Quote-like Operators"
	   in perlop.

   Non-function Keywords by Cross-reference
       perldata

       __DATA__
       __END__
	   These keywords are documented in "Special Literals" in perldata.

       perlmod

       BEGIN
       CHECK
       END
       INIT
       UNITCHECK
	   These compile phase keywords are documented in "BEGIN, UNITCHECK, CHECK, INIT and END"
	   in perlmod.

       perlobj

       DESTROY
	   This method keyword is documented in "Destructors" in perlobj.

       perlop

       and
       cmp
       eq
       ge
       gt
       if
       le
       lt
       ne
       not
       or
       x
       xor These operators are documented in perlop.

       perlsub

       AUTOLOAD
	   This keyword is documented in "Autoloading" in perlsub.

       perlsyn

       else
       elseif
       elsif
       for
       foreach
       unless
       until
       while
	   These flow-control keywords are documented in "Compound Statements" in perlsyn.

       default
       given
       when
	   These flow-control keywords related to the experimental switch feature are documented
	   in "Switch Statements" in perlsyn .

perl v5.16.3				    2013-03-04				      PERLFUNC(1)
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