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RedHat 9 (Linux i386) - man page for perlport (redhat section 1)

PERLPORT(1)			 Perl Programmers Reference Guide		      PERLPORT(1)

NAME
       perlport - Writing portable Perl

DESCRIPTION
       Perl runs on numerous operating systems.  While most of them share much in common, they
       also have their own unique features.

       This document is meant to help you to find out what constitutes portable Perl code.  That
       way once you make a decision to write portably, you know where the lines are drawn, and
       you can stay within them.

       There is a tradeoff between taking full advantage of one particular type of computer and
       taking advantage of a full range of them.  Naturally, as you broaden your range and become
       more diverse, the common factors drop, and you are left with an increasingly smaller area
       of common ground in which you can operate to accomplish a particular task.  Thus, when you
       begin attacking a problem, it is important to consider under which part of the tradeoff
       curve you want to operate.  Specifically, you must decide whether it is important that the
       task that you are coding have the full generality of being portable, or whether to just
       get the job done right now.  This is the hardest choice to be made.  The rest is easy,
       because Perl provides many choices, whichever way you want to approach your problem.

       Looking at it another way, writing portable code is usually about willfully limiting your
       available choices.  Naturally, it takes discipline and sacrifice to do that.  The product
       of portability and convenience may be a constant.  You have been warned.

       Be aware of two important points:

       Not all Perl programs have to be portable
	   There is no reason you should not use Perl as a language to glue Unix tools together,
	   or to prototype a Macintosh application, or to manage the Windows registry.	If it
	   makes no sense to aim for portability for one reason or another in a given program,
	   then don't bother.

       Nearly all of Perl already is portable
	   Don't be fooled into thinking that it is hard to create portable Perl code.	It isn't.
	   Perl tries its level-best to bridge the gaps between what's available on different
	   platforms, and all the means available to use those features.  Thus almost all Perl
	   code runs on any machine without modification.  But there are some significant issues
	   in writing portable code, and this document is entirely about those issues.

       Here's the general rule: When you approach a task commonly done using a whole range of
       platforms, think about writing portable code.  That way, you don't sacrifice much by way
       of the implementation choices you can avail yourself of, and at the same time you can give
       your users lots of platform choices.  On the other hand, when you have to take advantage
       of some unique feature of a particular platform, as is often the case with systems pro-
       gramming (whether for Unix, Windows, Mac OS, VMS, etc.), consider writing platform-spe-
       cific code.

       When the code will run on only two or three operating systems, you may need to consider
       only the differences of those particular systems.  The important thing is to decide where
       the code will run and to be deliberate in your decision.

       The material below is separated into three main sections: main issues of portability
       ("ISSUES", platform-specific issues ("PLATFORMS", and built-in perl functions that behave
       differently on various ports ("FUNCTION IMPLEMENTATIONS".

       This information should not be considered complete; it includes possibly transient infor-
       mation about idiosyncrasies of some of the ports, almost all of which are in a state of
       constant evolution.  Thus, this material should be considered a perpetual work in progress
       ("<IMG SRC="yellow_sign.gif" ALT="Under Construction">").

ISSUES
       Newlines

       In most operating systems, lines in files are terminated by newlines.  Just what is used
       as a newline may vary from OS to OS.  Unix traditionally uses "\012", one type of DOSish
       I/O uses "\015\012", and Mac OS uses "\015".

       Perl uses "\n" to represent the "logical" newline, where what is logical may depend on the
       platform in use.  In MacPerl, "\n" always means "\015".	In DOSish perls, "\n" usually
       means "\012", but when accessing a file in "text" mode, STDIO translates it to (or from)
       "\015\012", depending on whether you're reading or writing.  Unix does the same thing on
       ttys in canonical mode.	"\015\012" is commonly referred to as CRLF.

       A common cause of unportable programs is the misuse of chop() to trim newlines:

	   # XXX UNPORTABLE!
	   while(<FILE>) {
	       chop;
	       @array = split(/:/);
	       #...
	   }

       You can get away with this on Unix and Mac OS (they have a single character end-of-line),
       but the same program will break under DOSish perls because you're only chop()ing half the
       end-of-line.  Instead, chomp() should be used to trim newlines.	The Dunce::Files module
       can help audit your code for misuses of chop().

       When dealing with binary files (or text files in binary mode) be sure to explicitly set $/
       to the appropriate value for your file format before using chomp().

       Because of the "text" mode translation, DOSish perls have limitations in using "seek" and
       "tell" on a file accessed in "text" mode.  Stick to "seek"-ing to locations you got from
       "tell" (and no others), and you are usually free to use "seek" and "tell" even in "text"
       mode.  Using "seek" or "tell" or other file operations may be non-portable.  If you use
       "binmode" on a file, however, you can usually "seek" and "tell" with arbitrary values in
       safety.

       A common misconception in socket programming is that "\n" eq "\012" everywhere.	When
       using protocols such as common Internet protocols, "\012" and "\015" are called for
       specifically, and the values of the logical "\n" and "\r" (carriage return) are not reli-
       able.

	   print SOCKET "Hi there, client!\r\n";      # WRONG
	   print SOCKET "Hi there, client!\015\012";  # RIGHT

       However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can be tedious and unsightly, as
       well as confusing to those maintaining the code.  As such, the Socket module supplies the
       Right Thing for those who want it.

	   use Socket qw(:DEFAULT :crlf);
	   print SOCKET "Hi there, client!$CRLF"      # RIGHT

       When reading from a socket, remember that the default input record separator $/ is "\n",
       but robust socket code will recognize as either "\012" or "\015\012" as end of line:

	   while (<SOCKET>) {
	       # ...
	   }

       Because both CRLF and LF end in LF, the input record separator can be set to LF and any CR
       stripped later.	Better to write:

	   use Socket qw(:DEFAULT :crlf);
	   local($/) = LF;	# not needed if $/ is already \012

	   while (<SOCKET>) {
	       s/$CR?$LF/\n/;	# not sure if socket uses LF or CRLF, OK
	   #   s/\015?\012/\n/; # same thing
	   }

       This example is preferred over the previous one--even for Unix platforms--because now any
       "\015"'s ("\cM"'s) are stripped out (and there was much rejoicing).

       Similarly, functions that return text data--such as a function that fetches a web
       page--should sometimes translate newlines before returning the data, if they've not yet
       been translated to the local newline representation.  A single line of code will often
       suffice:

	   $data =~ s/\015?\012/\n/g;
	   return $data;

       Some of this may be confusing.  Here's a handy reference to the ASCII CR and LF charac-
       ters.  You can print it out and stick it in your wallet.

	   LF  eq  \012  eq  \x0A  eq  \cJ  eq	chr(10)  eq  ASCII 10
	   CR  eq  \015  eq  \x0D  eq  \cM  eq	chr(13)  eq  ASCII 13

		    | Unix | DOS  | Mac  |
	       ---------------------------
	       \n   |  LF  |  LF  |  CR  |
	       \r   |  CR  |  CR  |  LF  |
	       \n * |  LF  | CRLF |  CR  |
	       \r * |  CR  |  CR  |  LF  |
	       ---------------------------
	       * text-mode STDIO

       The Unix column assumes that you are not accessing a serial line (like a tty) in canonical
       mode.  If you are, then CR on input becomes "\n", and "\n" on output becomes CRLF.

       These are just the most common definitions of "\n" and "\r" in Perl.  There may well be
       others.	For example, on an EBCDIC implementation such as z/OS (OS/390) or OS/400 (using
       the ILE, the PASE is ASCII-based) the above material is similar to "Unix" but the code
       numbers change:

	   LF  eq  \025  eq  \x15  eq		chr(21)  eq  CP-1047 21
	   LF  eq  \045  eq  \x25  eq  \cU  eq	chr(37)  eq  CP-0037 37
	   CR  eq  \015  eq  \x0D  eq  \cM  eq	chr(13)  eq  CP-1047 13
	   CR  eq  \015  eq  \x0D  eq  \cM  eq	chr(13)  eq  CP-0037 13

		    | z/OS | OS/400 |
	       ----------------------
	       \n   |  LF  |  LF    |
	       \r   |  CR  |  CR    |
	       \n * |  LF  |  LF    |
	       \r * |  CR  |  CR    |
	       ----------------------
	       * text-mode STDIO

       Numbers endianness and Width

       Different CPUs store integers and floating point numbers in different orders (called endi-
       anness) and widths (32-bit and 64-bit being the most common today).  This affects your
       programs when they attempt to transfer numbers in binary format from one CPU architecture
       to another, usually either "live" via network connection, or by storing the numbers to
       secondary storage such as a disk file or tape.

       Conflicting storage orders make utter mess out of the numbers.  If a little-endian host
       (Intel, VAX) stores 0x12345678 (305419896 in decimal), a big-endian host (Motorola, Sparc,
       PA) reads it as 0x78563412 (2018915346 in decimal).  Alpha and MIPS can be either: Digi-
       tal/Compaq used/uses them in little-endian mode; SGI/Cray uses them in big-endian mode.
       To avoid this problem in network (socket) connections use the "pack" and "unpack" formats
       "n" and "N", the "network" orders.  These are guaranteed to be portable.

       You can explore the endianness of your platform by unpacking a data structure packed in
       native format such as:

	   print unpack("h*", pack("s2", 1, 2)), "\n";
	   # '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
	   # '00100020' on e.g. Motorola 68040

       If you need to distinguish between endian architectures you could use either of the vari-
       ables set like so:

	   $is_big_endian   = unpack("h*", pack("s", 1)) =~ /01/;
	   $is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;

       Differing widths can cause truncation even between platforms of equal endianness.  The
       platform of shorter width loses the upper parts of the number.  There is no good solution
       for this problem except to avoid transferring or storing raw binary numbers.

       One can circumnavigate both these problems in two ways.	Either transfer and store numbers
       always in text format, instead of raw binary, or else consider using modules like
       Data::Dumper (included in the standard distribution as of Perl 5.005) and Storable
       (included as of perl 5.8).  Keeping all data as text significantly simplifies matters.

       The v-strings are portable only up to v2147483647(0x7FFFFFFF), that's how far EBCDIC, or
       more precisely UTF-EBCDIC will go.

       Files and Filesystems

       Most platforms these days structure files in a hierarchical fashion.  So, it is reasonably
       safe to assume that all platforms support the notion of a "path" to uniquely identify a
       file on the system.  How that path is really written, though, differs considerably.

       Although similar, file path specifications differ between Unix, Windows, Mac OS, OS/2,
       VMS, VOS, RISC OS, and probably others.	Unix, for example, is one of the few OSes that
       has the elegant idea of a single root directory.

       DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with "/" as path separator, or
       in their own idiosyncratic ways (such as having several root directories and various
       "unrooted" device files such NIL: and LPT:).

       Mac OS uses ":" as a path separator instead of "/".

       The filesystem may support neither hard links ("link") nor symbolic links ("symlink",
       "readlink", "lstat").

       The filesystem may support neither access timestamp nor change timestamp (meaning that
       about the only portable timestamp is the modification timestamp), or one second granular-
       ity of any timestamps (e.g. the FAT filesystem limits the time granularity to two sec-
       onds).

       The "inode change timestamp" (the "-C" filetest) may really be the "creation timestamp"
       (which it is not in UNIX).

       VOS perl can emulate Unix filenames with "/" as path separator.	The native pathname char-
       acters greater-than, less-than, number-sign, and percent-sign are always accepted.

       RISC OS perl can emulate Unix filenames with "/" as path separator, or go native and use
       "." for path separator and ":" to signal filesystems and disk names.

       Don't assume UNIX filesystem access semantics: that read, write, and execute are all the
       permissions there are, and even if they exist, that their semantics (for example what do
       r, w, and x mean on a directory) are the UNIX ones.  The various UNIX/POSIX compatibility
       layers usually try to make interfaces like chmod() work, but sometimes there simply is no
       good mapping.

       If all this is intimidating, have no (well, maybe only a little) fear.  There are modules
       that can help.  The File::Spec modules provide methods to do the Right Thing on whatever
       platform happens to be running the program.

	   use File::Spec::Functions;
	   chdir(updir());	  # go up one directory
	   $file = catfile(curdir(), 'temp', 'file.txt');
	   # on Unix and Win32, './temp/file.txt'
	   # on Mac OS, ':temp:file.txt'
	   # on VMS, '[.temp]file.txt'

       File::Spec is available in the standard distribution as of version 5.004_05.
       File::Spec::Functions is only in File::Spec 0.7 and later, and some versions of perl come
       with version 0.6.  If File::Spec is not updated to 0.7 or later, you must use the object-
       oriented interface from File::Spec (or upgrade File::Spec).

       In general, production code should not have file paths hardcoded.  Making them user-sup-
       plied or read from a configuration file is better, keeping in mind that file path syntax
       varies on different machines.

       This is especially noticeable in scripts like Makefiles and test suites, which often
       assume "/" as a path separator for subdirectories.

       Also of use is File::Basename from the standard distribution, which splits a pathname into
       pieces (base filename, full path to directory, and file suffix).

       Even when on a single platform (if you can call Unix a single platform), remember not to
       count on the existence or the contents of particular system-specific files or directories,
       like /etc/passwd, /etc/sendmail.conf, /etc/resolv.conf, or even /tmp/.  For example,
       /etc/passwd may exist but not contain the encrypted passwords, because the system is using
       some form of enhanced security.	Or it may not contain all the accounts, because the sys-
       tem is using NIS.  If code does need to rely on such a file, include a description of the
       file and its format in the code's documentation, then make it easy for the user to over-
       ride the default location of the file.

       Don't assume a text file will end with a newline.  They should, but people forget.

       Do not have two files or directories of the same name with different case, like test.pl
       and Test.pl, as many platforms have case-insensitive (or at least case-forgiving) file-
       names.  Also, try not to have non-word characters (except for ".") in the names, and keep
       them to the 8.3 convention, for maximum portability, onerous a burden though this may
       appear.

       Likewise, when using the AutoSplit module, try to keep your functions to 8.3 naming and
       case-insensitive conventions; or, at the least, make it so the resulting files have a
       unique (case-insensitively) first 8 characters.

       Whitespace in filenames is tolerated on most systems, but not all, and even on systems
       where it might be tolerated, some utilities might become confused by such whitespace.

       Many systems (DOS, VMS) cannot have more than one "." in their filenames.

       Don't assume ">" won't be the first character of a filename.  Always use "<" explicitly to
       open a file for reading, or even better, use the three-arg version of open, unless you
       want the user to be able to specify a pipe open.

	   open(FILE, '<', $existing_file) or die $!;

       If filenames might use strange characters, it is safest to open it with "sysopen" instead
       of "open".  "open" is magic and can translate characters like ">", "<", and "|", which may
       be the wrong thing to do.  (Sometimes, though, it's the right thing.)  Three-arg open can
       also help protect against this translation in cases where it is undesirable.

       Don't use ":" as a part of a filename since many systems use that for their own semantics
       (Mac OS Classic for separating pathname components, many networking schemes and utilities
       for separating the nodename and the pathname, and so on).  For the same reasons, avoid
       "@", ";" and "|".

       Don't assume that in pathnames you can collapse two leading slashes "//" into one: some
       networking and clustering filesystems have special semantics for that.  Let the operating
       system to sort it out.

       The portable filename characters as defined by ANSI C are

	a b c d e f g h i j k l m n o p q r t u v w x y z
	A B C D E F G H I J K L M N O P Q R T U V W X Y Z
	0 1 2 3 4 5 6 7 8 9
	. _ -

       and the "-" shouldn't be the first character.  If you want to be hypercorrect, stay case-
       insensitive and within the 8.3 naming convention (all the files and directories have to be
       unique within one directory if their names are lowercased and truncated to eight charac-
       ters before the ".", if any, and to three characters after the ".", if any).  (And do not
       use "."s in directory names.)

       System Interaction

       Not all platforms provide a command line.  These are usually platforms that rely primarily
       on a Graphical User Interface (GUI) for user interaction.  A program requiring a command
       line interface might not work everywhere.  This is probably for the user of the program to
       deal with, so don't stay up late worrying about it.

       Some platforms can't delete or rename files held open by the system, this limitation may
       also apply to changing filesystem metainformation like file permissions or owners.  Remem-
       ber to "close" files when you are done with them.  Don't "unlink" or "rename" an open
       file.  Don't "tie" or "open" a file already tied or opened; "untie" or "close" it first.

       Don't open the same file more than once at a time for writing, as some operating systems
       put mandatory locks on such files.

       Don't assume that write/modify permission on a directory gives the right to add or delete
       files/directories in that directory.  That is filesystem specific: in some filesystems you
       need write/modify permission also (or even just) in the file/directory itself.  In some
       filesystems (AFS, DFS) the permission to add/delete directory entries is a completely sep-
       arate permission.

       Don't assume that a single "unlink" completely gets rid of the file: some filesystems
       (most notably the ones in VMS) have versioned filesystems, and unlink() removes only the
       most recent one (it doesn't remove all the versions because by default the native tools on
       those platforms remove just the most recent version, too).  The portable idiom to remove
       all the versions of a file is

	   1 while unlink "file";

       This will terminate if the file is undeleteable for some reason (protected, not there, and
       so on).

       Don't count on a specific environment variable existing in %ENV.  Don't count on %ENV
       entries being case-sensitive, or even case-preserving.  Don't try to clear %ENV by saying
       "%ENV = ();", or, if you really have to, make it conditional on "$^O ne 'VMS'" since in
       VMS the %ENV table is much more than a per-process key-value string table.

       Don't count on signals or %SIG for anything.

       Don't count on filename globbing.  Use "opendir", "readdir", and "closedir" instead.

       Don't count on per-program environment variables, or per-program current directories.

       Don't count on specific values of $!, neither numeric nor especially the strings values--
       users may switch their locales causing error messages to be translated into their lan-
       guages.	If you can trust a POSIXish environment, you can portably use the symbols defined
       by the Errno module, like ENOENT.  And don't trust on the values of $!  at all except
       immediately after a failed system call.

       Command names versus file pathnames

       Don't assume that the name used to invoke a command or program with "system" or "exec" can
       also be used to test for the existence of the file that holds the executable code for that
       command or program.  First, many systems have "internal" commands that are built-in to the
       shell or OS and while these commands can be invoked, there is no corresponding file.  Sec-
       ond, some operating systems (e.g., Cygwin, DJGPP, OS/2, and VOS) have required suffixes
       for executable files; these suffixes are generally permitted on the command name but are
       not required.  Thus, a command like "perl" might exist in a file named "perl", "perl.exe",
       or "perl.pm", depending on the operating system.  The variable "_exe" in the Config module
       holds the executable suffix, if any.  Third, the VMS port carefully sets up $^X and $Con-
       fig{perlpath} so that no further processing is required.  This is just as well, because
       the matching regular expression used below would then have to deal with a possible trail-
       ing version number in the VMS file name.

       To convert $^X to a file pathname, taking account of the requirements of the various oper-
       ating system possibilities, say:
	 use Config;
	 $thisperl = $^X;
	 if ($^O ne 'VMS')
	    {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}

       To convert $Config{perlpath} to a file pathname, say:
	 use Config;
	 $thisperl = $Config{perlpath};
	 if ($^O ne 'VMS')
	    {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}

       Interprocess Communication (IPC)

       In general, don't directly access the system in code meant to be portable.  That means, no
       "system", "exec", "fork", "pipe", ``, "qx//", "open" with a "|", nor any of the other
       things that makes being a perl hacker worth being.

       Commands that launch external processes are generally supported on most platforms (though
       many of them do not support any type of forking).  The problem with using them arises from
       what you invoke them on.  External tools are often named differently on different plat-
       forms, may not be available in the same location, might accept different arguments, can
       behave differently, and often present their results in a platform-dependent way.  Thus,
       you should seldom depend on them to produce consistent results. (Then again, if you're
       calling netstat -a, you probably don't expect it to run on both Unix and CP/M.)

       One especially common bit of Perl code is opening a pipe to sendmail:

	   open(MAIL, '|/usr/lib/sendmail -t')
	       or die "cannot fork sendmail: $!";

       This is fine for systems programming when sendmail is known to be available.  But it is
       not fine for many non-Unix systems, and even some Unix systems that may not have sendmail
       installed.  If a portable solution is needed, see the various distributions on CPAN that
       deal with it.  Mail::Mailer and Mail::Send in the MailTools distribution are commonly
       used, and provide several mailing methods, including mail, sendmail, and direct SMTP (via
       Net::SMTP) if a mail transfer agent is not available.  Mail::Sendmail is a standalone mod-
       ule that provides simple, platform-independent mailing.

       The Unix System V IPC ("msg*(), sem*(), shm*()") is not available even on all Unix plat-
       forms.

       Do not use either the bare result of "pack("N", 10, 20, 30, 40)" or bare v-strings (such
       as "v10.20.30.40") to represent IPv4 addresses: both forms just pack the four bytes into
       network order.  That this would be equal to the C language "in_addr" struct (which is what
       the socket code internally uses) is not guaranteed.  To be portable use the routines of
       the Socket extension, such as "inet_aton()", "inet_ntoa()", and "sockaddr_in()".

       The rule of thumb for portable code is: Do it all in portable Perl, or use a module (that
       may internally implement it with platform-specific code, but expose a common interface).

       External Subroutines (XS)

       XS code can usually be made to work with any platform, but dependent libraries, header
       files, etc., might not be readily available or portable, or the XS code itself might be
       platform-specific, just as Perl code might be.  If the libraries and headers are portable,
       then it is normally reasonable to make sure the XS code is portable, too.

       A different type of portability issue arises when writing XS code: availability of a C
       compiler on the end-user's system.  C brings with it its own portability issues, and writ-
       ing XS code will expose you to some of those.  Writing purely in Perl is an easier way to
       achieve portability.

       Standard Modules

       In general, the standard modules work across platforms.	Notable exceptions are the CPAN
       module (which currently makes connections to external programs that may not be available),
       platform-specific modules (like ExtUtils::MM_VMS), and DBM modules.

       There is no one DBM module available on all platforms.  SDBM_File and the others are gen-
       erally available on all Unix and DOSish ports, but not in MacPerl, where only NBDM_File
       and DB_File are available.

       The good news is that at least some DBM module should be available, and AnyDBM_File will
       use whichever module it can find.  Of course, then the code needs to be fairly strict,
       dropping to the greatest common factor (e.g., not exceeding 1K for each record), so that
       it will work with any DBM module.  See AnyDBM_File for more details.

       Time and Date

       The system's notion of time of day and calendar date is controlled in widely different
       ways.  Don't assume the timezone is stored in $ENV{TZ}, and even if it is, don't assume
       that you can control the timezone through that variable.  Don't assume anything about the
       three-letter timezone abbreviations (for example that MST would be the Mountain Standard
       Time, it's been known to stand for Moscow Standard Time).  If you need to use timezones,
       express them in some unambiguous format like the exact number of minutes offset from UTC,
       or the POSIX timezone format.

       Don't assume that the epoch starts at 00:00:00, January 1, 1970, because that is OS- and
       implementation-specific.  It is better to store a date in an unambiguous representation.
       The ISO 8601 standard defines YYYY-MM-DD as the date format, or YYYY-MM-DDTHH-MM-SS
       (that's a literal "T" separating the date from the time).  Please do use the ISO 8601
       instead of making us to guess what date 02/03/04 might be.  ISO 8601 even sorts nicely
       as-is.  A text representation (like "1987-12-18") can be easily converted into an OS-spe-
       cific value using a module like Date::Parse.  An array of values, such as those returned
       by "localtime", can be converted to an OS-specific representation using Time::Local.

       When calculating specific times, such as for tests in time or date modules, it may be
       appropriate to calculate an offset for the epoch.

	   require Time::Local;
	   $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);

       The value for $offset in Unix will be 0, but in Mac OS will be some large number.  $offset
       can then be added to a Unix time value to get what should be the proper value on any sys-
       tem.

       Character sets and character encoding

       Assume very little about character sets.

       Assume nothing about numerical values ("ord", "chr") of characters.  Do not use explicit
       code point ranges (like \xHH-\xHH); use for example symbolic character classes like
       "[:print:]".

       Do not assume that the alphabetic characters are encoded contiguously (in the numeric
       sense).	There may be gaps.

       Do not assume anything about the ordering of the characters.  The lowercase letters may
       come before or after the uppercase letters; the lowercase and uppercase may be interlaced
       so that both `a' and `A' come before `b'; the accented and other international characters
       may be interlaced so that ae comes before `b'.

       Internationalisation

       If you may assume POSIX (a rather large assumption), you may read more about the POSIX
       locale system from perllocale.  The locale system at least attempts to make things a lit-
       tle bit more portable, or at least more convenient and native-friendly for non-English
       users.  The system affects character sets and encoding, and date and time format-
       ting--amongst other things.

       If you really want to be international, you should consider Unicode.  See perluniintro and
       perlunicode for more information.

       System Resources

       If your code is destined for systems with severely constrained (or missing!) virtual mem-
       ory systems then you want to be especially mindful of avoiding wasteful constructs such
       as:

	   # NOTE: this is no longer "bad" in perl5.005
	   for (0..10000000) {} 		      # bad
	   for (my $x = 0; $x <= 10000000; ++$x) {}   # good

	   @lines = <VERY_LARGE_FILE>;		      # bad

	   while (<FILE>) {$file .= $_} 	      # sometimes bad
	   $file = join('', <FILE>);		      # better

       The last two constructs may appear unintuitive to most people.  The first repeatedly grows
       a string, whereas the second allocates a large chunk of memory in one go.  On some sys-
       tems, the second is more efficient that the first.

       Security

       Most multi-user platforms provide basic levels of security, usually implemented at the
       filesystem level.  Some, however, do not-- unfortunately.  Thus the notion of user id, or
       "home" directory, or even the state of being logged-in, may be unrecognizable on many
       platforms.  If you write programs that are security-conscious, it is usually best to know
       what type of system you will be running under so that you can write code explicitly for
       that platform (or class of platforms).

       Don't assume the UNIX filesystem access semantics: the operating system or the filesystem
       may be using some ACL systems, which are richer languages than the usual rwx.  Even if the
       rwx exist, their semantics might be different.

       (From security viewpoint testing for permissions before attempting to do something is
       silly anyway: if one tries this, there is potential for race conditions-- someone or some-
       thing might change the permissions between the permissions check and the actual operation.
       Just try the operation.)

       Don't assume the UNIX user and group semantics: especially, don't expect the $< and $> (or
       the $( and $)) to work for switching identities (or memberships).

       Don't assume set-uid and set-gid semantics. (And even if you do, think twice: set-uid and
       set-gid are a known can of security worms.)

       Style

       For those times when it is necessary to have platform-specific code, consider keeping the
       platform-specific code in one place, making porting to other platforms easier.  Use the
       Config module and the special variable $^O to differentiate platforms, as described in
       "PLATFORMS".

       Be careful in the tests you supply with your module or programs.  Module code may be fully
       portable, but its tests might not be.  This often happens when tests spawn off other pro-
       cesses or call external programs to aid in the testing, or when (as noted above) the tests
       assume certain things about the filesystem and paths.  Be careful not to depend on a spe-
       cific output style for errors, such as when checking $! after a failed system call.  Using
       $! for anything else than displaying it as output is doubtful (though see the Errno module
       for testing reasonably portably for error value). Some platforms expect a certain output
       format, and Perl on those platforms may have been adjusted accordingly.	Most specifi-
       cally, don't anchor a regex when testing an error value.

CPAN Testers
       Modules uploaded to CPAN are tested by a variety of volunteers on different platforms.
       These CPAN testers are notified by mail of each new upload, and reply to the list with
       PASS, FAIL, NA (not applicable to this platform), or UNKNOWN (unknown), along with any
       relevant notations.

       The purpose of the testing is twofold: one, to help developers fix any problems in their
       code that crop up because of lack of testing on other platforms; two, to provide users
       with information about whether a given module works on a given platform.

       Mailing list: cpan-testers@perl.org
       Testing results: http://testers.cpan.org/

PLATFORMS
       As of version 5.002, Perl is built with a $^O variable that indicates the operating system
       it was built on.  This was implemented to help speed up code that would otherwise have to
       "use Config" and use the value of $Config{osname}.  Of course, to get more detailed infor-
       mation about the system, looking into %Config is certainly recommended.

       %Config cannot always be trusted, however, because it was built at compile time.  If perl
       was built in one place, then transferred elsewhere, some values may be wrong.  The values
       may even have been edited after the fact.

       Unix

       Perl works on a bewildering variety of Unix and Unix-like platforms (see e.g. most of the
       files in the hints/ directory in the source code kit).  On most of these systems, the
       value of $^O (hence $Config{'osname'}, too) is determined either by lowercasing and strip-
       ping punctuation from the first field of the string returned by typing "uname -a" (or a
       similar command) at the shell prompt or by testing the file system for the presence of
       uniquely named files such as a kernel or header file.  Here, for example, are a few of the
       more popular Unix flavors:

	   uname	 $^O	    $Config{'archname'}
	   --------------------------------------------
	   AIX		 aix	    aix
	   BSD/OS	 bsdos	    i386-bsdos
	   Darwin	 darwin     darwin
	   dgux 	 dgux	    AViiON-dgux
	   DYNIX/ptx	 dynixptx   i386-dynixptx
	   FreeBSD	 freebsd    freebsd-i386
	   Linux	 linux	    arm-linux
	   Linux	 linux	    i386-linux
	   Linux	 linux	    i586-linux
	   Linux	 linux	    ppc-linux
	   HP-UX	 hpux	    PA-RISC1.1
	   IRIX 	 irix	    irix
	   Mac OS X	 darwin     darwin
	   MachTen PPC	 machten    powerpc-machten
	   NeXT 3	 next	    next-fat
	   NeXT 4	 next	    OPENSTEP-Mach
	   openbsd	 openbsd    i386-openbsd
	   OSF1 	 dec_osf    alpha-dec_osf
	   reliantunix-n svr4	    RM400-svr4
	   SCO_SV	 sco_sv     i386-sco_sv
	   SINIX-N	 svr4	    RM400-svr4
	   sn4609	 unicos     CRAY_C90-unicos
	   sn6521	 unicosmk   t3e-unicosmk
	   sn9617	 unicos     CRAY_J90-unicos
	   SunOS	 solaris    sun4-solaris
	   SunOS	 solaris    i86pc-solaris
	   SunOS4	 sunos	    sun4-sunos

       Because the value of $Config{archname} may depend on the hardware architecture, it can
       vary more than the value of $^O.

       DOS and Derivatives

       Perl has long been ported to Intel-style microcomputers running under systems like PC-DOS,
       MS-DOS, OS/2, and most Windows platforms you can bring yourself to mention (except for
       Windows CE, if you count that).	Users familiar with COMMAND.COM or CMD.EXE style shells
       should be aware that each of these file specifications may have subtle differences:

	   $filespec0 = "c:/foo/bar/file.txt";
	   $filespec1 = "c:\\foo\\bar\\file.txt";
	   $filespec2 = 'c:\foo\bar\file.txt';
	   $filespec3 = 'c:\\foo\\bar\\file.txt';

       System calls accept either "/" or "\" as the path separator.  However, many command-line
       utilities of DOS vintage treat "/" as the option prefix, so may get confused by filenames
       containing "/".	Aside from calling any external programs, "/" will work just fine, and
       probably better, as it is more consistent with popular usage, and avoids the problem of
       remembering what to backwhack and what not to.

       The DOS FAT filesystem can accommodate only "8.3" style filenames.  Under the "case-insen-
       sitive, but case-preserving" HPFS (OS/2) and NTFS (NT) filesystems you may have to be
       careful about case returned with functions like "readdir" or used with functions like
       "open" or "opendir".

       DOS also treats several filenames as special, such as AUX, PRN, NUL, CON, COM1, LPT1,
       LPT2, etc.  Unfortunately, sometimes these filenames won't even work if you include an
       explicit directory prefix.  It is best to avoid such filenames, if you want your code to
       be portable to DOS and its derivatives.	It's hard to know what these all are, unfortu-
       nately.

       Users of these operating systems may also wish to make use of scripts such as pl2bat.bat
       or pl2cmd to put wrappers around your scripts.

       Newline ("\n") is translated as "\015\012" by STDIO when reading from and writing to files
       (see "Newlines").  "binmode(FILEHANDLE)" will keep "\n" translated as "\012" for that
       filehandle.  Since it is a no-op on other systems, "binmode" should be used for cross-
       platform code that deals with binary data.  That's assuming you realize in advance that
       your data is in binary.	General-purpose programs should often assume nothing about their
       data.

       The $^O variable and the $Config{archname} values for various DOSish perls are as follows:

	    OS		  $^O	   $Config{archname}   ID    Version
	    --------------------------------------------------------
	    MS-DOS	  dos	     ?
	    PC-DOS	  dos	     ?
	    OS/2	  os2	     ?
	    Windows 3.1   ?	     ?		       0      3 01
	    Windows 95	  MSWin32    MSWin32-x86       1      4 00
	    Windows 98	  MSWin32    MSWin32-x86       1      4 10
	    Windows ME	  MSWin32    MSWin32-x86       1      ?
	    Windows NT	  MSWin32    MSWin32-x86       2      4 xx
	    Windows NT	  MSWin32    MSWin32-ALPHA     2      4 xx
	    Windows NT	  MSWin32    MSWin32-ppc       2      4 xx
	    Windows 2000  MSWin32    MSWin32-x86       2      5 xx
	    Windows XP	  MSWin32    MSWin32-x86       2      ?
	    Windows CE	  MSWin32    ?		       3
	    Cygwin	  cygwin     ?

       The various MSWin32 Perl's can distinguish the OS they are running on via the value of the
       fifth element of the list returned from Win32::GetOSVersion().  For example:

	   if ($^O eq 'MSWin32') {
	       my @os_version_info = Win32::GetOSVersion();
	       print +('3.1','95','NT')[$os_version_info[4]],"\n";
	   }

       There are also Win32::IsWinNT() and Win32::IsWin95(), try "perldoc Win32", and as of lib-
       win32 0.19 (not part of the core Perl distribution) Win32::GetOSName().	The very portable
       POSIX::uname() will work too:

	   c:\> perl -MPOSIX -we "print join '|', uname"
	   Windows NT|moonru|5.0|Build 2195 (Service Pack 2)|x86

       Also see:

       o   The djgpp environment for DOS, http://www.delorie.com/djgpp/ and perldos.

       o   The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
	   http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html or
	   ftp://hobbes.nmsu.edu/pub/os2/dev/emx/  Also perlos2.

       o   Build instructions for Win32 in perlwin32, or under the Cygnus environment in perlcyg-
	   win.

       o   The "Win32::*" modules in Win32.

       o   The ActiveState Pages, http://www.activestate.com/

       o   The Cygwin environment for Win32; README.cygwin (installed as perlcygwin),
	   http://www.cygwin.com/

       o   The U/WIN environment for Win32, http://www.research.att.com/sw/tools/uwin/

       o   Build instructions for OS/2, perlos2

       Mac OS

       Any module requiring XS compilation is right out for most people, because MacPerl is built
       using non-free (and non-cheap!) compilers.  Some XS modules that can work with MacPerl are
       built and distributed in binary form on CPAN.

       Directories are specified as:

	   volume:folder:file		   for absolute pathnames
	   volume:folder:		   for absolute pathnames
	   :folder:file 		   for relative pathnames
	   :folder:			   for relative pathnames
	   :file			   for relative pathnames
	   file 			   for relative pathnames

       Files are stored in the directory in alphabetical order.  Filenames are limited to 31
       characters, and may include any character except for null and ":", which is reserved as
       the path separator.

       Instead of "flock", see "FSpSetFLock" and "FSpRstFLock" in the Mac::Files module, or
       "chmod(0444, ...)" and "chmod(0666, ...)".

       In the MacPerl application, you can't run a program from the command line; programs that
       expect @ARGV to be populated can be edited with something like the following, which brings
       up a dialog box asking for the command line arguments.

	   if (!@ARGV) {
	       @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
	   }

       A MacPerl script saved as a "droplet" will populate @ARGV with the full pathnames of the
       files dropped onto the script.

       Mac users can run programs under a type of command line interface under MPW (Macintosh
       Programmer's Workshop, a free development environment from Apple).  MacPerl was first
       introduced as an MPW tool, and MPW can be used like a shell:

	   perl myscript.plx some arguments

       ToolServer is another app from Apple that provides access to MPW tools from MPW and the
       MacPerl app, which allows MacPerl programs to use "system", backticks, and piped "open".

       "Mac OS" is the proper name for the operating system, but the value in $^O is "MacOS".  To
       determine architecture, version, or whether the application or MPW tool version is run-
       ning, check:

	   $is_app    = $MacPerl::Version =~ /App/;
	   $is_tool   = $MacPerl::Version =~ /MPW/;
	   ($version) = $MacPerl::Version =~ /^(\S+)/;
	   $is_ppc    = $MacPerl::Architecture eq 'MacPPC';
	   $is_68k    = $MacPerl::Architecture eq 'Mac68K';

       Mac OS X, based on NeXT's OpenStep OS, runs MacPerl natively, under the "Classic" environ-
       ment.  There is no "Carbon" version of MacPerl to run under the primary Mac OS X environ-
       ment.  Mac OS X and its Open Source version, Darwin, both run Unix perl natively.

       Also see:

       o   MacPerl Development, http://dev.macperl.org/ .

       o   The MacPerl Pages, http://www.macperl.com/ .

       o   The MacPerl mailing lists, http://lists.perl.org/ .

       VMS

       Perl on VMS is discussed in perlvms in the perl distribution.  Perl on VMS can accept
       either VMS- or Unix-style file specifications as in either of the following:

	   $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
	   $ perl -ne "print if /perl_setup/i" /sys$login/login.com

       but not a mixture of both as in:

	   $ perl -ne "print if /perl_setup/i" sys$login:/login.com
	   Can't open sys$login:/login.com: file specification syntax error

       Interacting with Perl from the Digital Command Language (DCL) shell often requires a dif-
       ferent set of quotation marks than Unix shells do.  For example:

	   $ perl -e "print ""Hello, world.\n"""
	   Hello, world.

       There are several ways to wrap your perl scripts in DCL .COM files, if you are so
       inclined.  For example:

	   $ write sys$output "Hello from DCL!"
	   $ if p1 .eqs. ""
	   $ then perl -x 'f$environment("PROCEDURE")
	   $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
	   $ deck/dollars="__END__"
	   #!/usr/bin/perl

	   print "Hello from Perl!\n";

	   __END__
	   $ endif

       Do take care with "$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT" if your perl-in-DCL script
       expects to do things like "$read = <STDIN>;".

       Filenames are in the format "name.extension;version".  The maximum length for filenames is
       39 characters, and the maximum length for extensions is also 39 characters.  Version is a
       number from 1 to 32767.	Valid characters are "/[A-Z0-9$_-]/".

       VMS's RMS filesystem is case-insensitive and does not preserve case.  "readdir" returns
       lowercased filenames, but specifying a file for opening remains case-insensitive.  Files
       without extensions have a trailing period on them, so doing a "readdir" with a file named
       A.;5 will return a. (though that file could be opened with "open(FH, 'A')").

       RMS had an eight level limit on directory depths from any rooted logical (allowing 16 lev-
       els overall) prior to VMS 7.2.  Hence "PERL_ROOT:[LIB.2.3.4.5.6.7.8]" is a valid directory
       specification but "PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]" is not.  Makefile.PL authors might
       have to take this into account, but at least they can refer to the former as
       "/PERL_ROOT/lib/2/3/4/5/6/7/8/".

       The VMS::Filespec module, which gets installed as part of the build process on VMS, is a
       pure Perl module that can easily be installed on non-VMS platforms and can be helpful for
       conversions to and from RMS native formats.

       What "\n" represents depends on the type of file opened.  It usually represents "\012" but
       it could also be "\015", "\012", "\015\012", "\000", "\040", or nothing depending on the
       file organiztion and record format.  The VMS::Stdio module provides access to the special
       fopen() requirements of files with unusual attributes on VMS.

       TCP/IP stacks are optional on VMS, so socket routines might not be implemented.	UDP sock-
       ets may not be supported.

       The value of $^O on OpenVMS is "VMS".  To determine the architecture that you are running
       on without resorting to loading all of %Config you can examine the content of the @INC
       array like so:

	   if (grep(/VMS_AXP/, @INC)) {
	       print "I'm on Alpha!\n";

	   } elsif (grep(/VMS_VAX/, @INC)) {
	       print "I'm on VAX!\n";

	   } else {
	       print "I'm not so sure about where $^O is...\n";
	   }

       On VMS, perl determines the UTC offset from the "SYS$TIMEZONE_DIFFERENTIAL" logical name.
       Although the VMS epoch began at 17-NOV-1858 00:00:00.00, calls to "localtime" are adjusted
       to count offsets from 01-JAN-1970 00:00:00.00, just like Unix.

       Also see:

       o   README.vms (installed as README_vms), perlvms

       o   vmsperl list, majordomo@perl.org

	   (Put the words "subscribe vmsperl" in message body.)

       o   vmsperl on the web, http://www.sidhe.org/vmsperl/index.html

       VOS

       Perl on VOS is discussed in README.vos in the perl distribution (installed as perlvos).
       Perl on VOS can accept either VOS- or Unix-style file specifications as in either of the
       following:

	   C<< $ perl -ne "print if /perl_setup/i" >system>notices >>
	   C<< $ perl -ne "print if /perl_setup/i" /system/notices >>

       or even a mixture of both as in:

	   C<< $ perl -ne "print if /perl_setup/i" >system/notices >>

       Even though VOS allows the slash character to appear in object names, because the VOS port
       of Perl interprets it as a pathname delimiting character, VOS files, directories, or links
       whose names contain a slash character cannot be processed.  Such files must be renamed
       before they can be processed by Perl.  Note that VOS limits file names to 32 or fewer
       characters.

       Perl on VOS can be built using two different compilers and two different versions of the
       POSIX runtime.  The recommended method for building full Perl is with the GNU C compiler
       and the generally-available version of VOS POSIX support.  See README.vos (installed as
       perlvos) for restrictions that apply when Perl is built using the VOS Standard C compiler
       or the alpha version of VOS POSIX support.

       The value of $^O on VOS is "VOS".  To determine the architecture that you are running on
       without resorting to loading all of %Config you can examine the content of the @INC array
       like so:

	   if ($^O =~ /VOS/) {
	       print "I'm on a Stratus box!\n";
	   } else {
	       print "I'm not on a Stratus box!\n";
	       die;
	   }

	   if (grep(/860/, @INC)) {
	       print "This box is a Stratus XA/R!\n";

	   } elsif (grep(/7100/, @INC)) {
	       print "This box is a Stratus HP 7100 or 8xxx!\n";

	   } elsif (grep(/8000/, @INC)) {
	       print "This box is a Stratus HP 8xxx!\n";

	   } else {
	       print "This box is a Stratus 68K!\n";
	   }

       Also see:

       o   README.vos (installed as perlvos)

       o   The VOS mailing list.

	   There is no specific mailing list for Perl on VOS.  You can post comments to the
	   comp.sys.stratus newsgroup, or subscribe to the general Stratus mailing list.  Send a
	   letter with "subscribe Info-Stratus" in the message body to major-
	   domo@list.stratagy.com.

       o   VOS Perl on the web at http://ftp.stratus.com/pub/vos/posix/posix.html

       EBCDIC Platforms

       Recent versions of Perl have been ported to platforms such as OS/400 on AS/400 minicomput-
       ers as well as OS/390, VM/ESA, and BS2000 for S/390 Mainframes.	Such computers use EBCDIC
       character sets internally (usually Character Code Set ID 0037 for OS/400 and either 1047
       or POSIX-BC for S/390 systems).	On the mainframe perl currently works under the "Unix
       system services for OS/390" (formerly known as OpenEdition), VM/ESA OpenEdition, or the
       BS200 POSIX-BC system (BS2000 is supported in perl 5.6 and greater).  See perlos390 for
       details.  Note that for OS/400 there is also a port of Perl 5.8.1/5.9.0 or later to the
       PASE which is ASCII-based (as opposed to ILE which is EBCDIC-based), see perlos400.

       As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix sub-systems do not sup-
       port the "#!" shebang trick for script invocation.  Hence, on OS/390 and VM/ESA perl
       scripts can be executed with a header similar to the following simple script:

	   : # use perl
	       eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
		   if 0;
	   #!/usr/local/bin/perl     # just a comment really

	   print "Hello from perl!\n";

       OS/390 will support the "#!" shebang trick in release 2.8 and beyond.  Calls to "system"
       and backticks can use POSIX shell syntax on all S/390 systems.

       On the AS/400, if PERL5 is in your library list, you may need to wrap your perl scripts in
       a CL procedure to invoke them like so:

	   BEGIN
	     CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
	   ENDPGM

       This will invoke the perl script hello.pl in the root of the QOpenSys file system.  On the
       AS/400 calls to "system" or backticks must use CL syntax.

       On these platforms, bear in mind that the EBCDIC character set may have an effect on what
       happens with some perl functions (such as "chr", "pack", "print", "printf", "ord", "sort",
       "sprintf", "unpack"), as well as bit-fiddling with ASCII constants using operators like
       "^", "&" and "|", not to mention dealing with socket interfaces to ASCII computers (see
       "Newlines").

       Fortunately, most web servers for the mainframe will correctly translate the "\n" in the
       following statement to its ASCII equivalent ("\r" is the same under both Unix and OS/390 &
       VM/ESA):

	   print "Content-type: text/html\r\n\r\n";

       The values of $^O on some of these platforms includes:

	   uname	 $^O	    $Config{'archname'}
	   --------------------------------------------
	   OS/390	 os390	    os390
	   OS400	 os400	    os400
	   POSIX-BC	 posix-bc   BS2000-posix-bc
	   VM/ESA	 vmesa	    vmesa

       Some simple tricks for determining if you are running on an EBCDIC platform could include
       any of the following (perhaps all):

	   if ("\t" eq "\05")	{ print "EBCDIC may be spoken here!\n"; }

	   if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }

	   if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }

       One thing you may not want to rely on is the EBCDIC encoding of punctuation characters
       since these may differ from code page to code page (and once your module or script is
       rumoured to work with EBCDIC, folks will want it to work with all EBCDIC character sets).

       Also see:

       o   *

	   perlos390, README.os390, perlbs2000, README.vmesa, perlebcdic.

       o   The perl-mvs@perl.org list is for discussion of porting issues as well as general
	   usage issues for all EBCDIC Perls.  Send a message body of "subscribe perl-mvs" to
	   majordomo@perl.org.

       o   AS/400 Perl information at http://as400.rochester.ibm.com/ as well as on CPAN in the
	   ports/ directory.

       Acorn RISC OS

       Because Acorns use ASCII with newlines ("\n") in text files as "\012" like Unix, and
       because Unix filename emulation is turned on by default, most simple scripts will probably
       work "out of the box".  The native filesystem is modular, and individual filesystems are
       free to be case-sensitive or insensitive, and are usually case-preserving.  Some native
       filesystems have name length limits, which file and directory names are silently truncated
       to fit.	Scripts should be aware that the standard filesystem currently has a name length
       limit of 10 characters, with up to 77 items in a directory, but other filesystems may not
       impose such limitations.

       Native filenames are of the form

	   Filesystem#Special_Field::DiskName.$.Directory.Directory.File

       where

	   Special_Field is not usually present, but may contain . and $ .
	   Filesystem =~ m|[A-Za-z0-9_]|
	   DsicName   =~ m|[A-Za-z0-9_/]|
	   $ represents the root directory
	   . is the path separator
	   @ is the current directory (per filesystem but machine global)
	   ^ is the parent directory
	   Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|

       The default filename translation is roughly "tr|/.|./|;"

       Note that ""ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File'" and that the second stage
       of "$" interpolation in regular expressions will fall foul of the $. if scripts are not
       careful.

       Logical paths specified by system variables containing comma-separated search lists are
       also allowed; hence "System:Modules" is a valid filename, and the filesystem will prefix
       "Modules" with each section of "System$Path" until a name is made that points to an object
       on disk.  Writing to a new file "System:Modules" would be allowed only if "System$Path"
       contains a single item list.  The filesystem will also expand system variables in file-
       names if enclosed in angle brackets, so "<System$Dir>.Modules" would look for the file
       "$ENV{'System$Dir'} . 'Modules'".  The obvious implication of this is that fully qualified
       filenames can start with "<>" and should be protected when "open" is used for input.

       Because "." was in use as a directory separator and filenames could not be assumed to be
       unique after 10 characters, Acorn implemented the C compiler to strip the trailing ".c"
       ".h" ".s" and ".o" suffix from filenames specified in source code and store the respective
       files in subdirectories named after the suffix.	Hence files are translated:

	   foo.h	   h.foo
	   C:foo.h	   C:h.foo	  (logical path variable)
	   sys/os.h	   sys.h.os	  (C compiler groks Unix-speak)
	   10charname.c    c.10charname
	   10charname.o    o.10charname
	   11charname_.c   c.11charname   (assuming filesystem truncates at 10)

       The Unix emulation library's translation of filenames to native assumes that this sort of
       translation is required, and it allows a user-defined list of known suffixes that it will
       transpose in this fashion.  This may seem transparent, but consider that with these rules
       "foo/bar/baz.h" and "foo/bar/h/baz" both map to "foo.bar.h.baz", and that "readdir" and
       "glob" cannot and do not attempt to emulate the reverse mapping.  Other "."'s in filenames
       are translated to "/".

       As implied above, the environment accessed through %ENV is global, and the convention is
       that program specific environment variables are of the form "Program$Name".  Each filesys-
       tem maintains a current directory, and the current filesystem's current directory is the
       global current directory.  Consequently, sociable programs don't change the current direc-
       tory but rely on full pathnames, and programs (and Makefiles) cannot assume that they can
       spawn a child process which can change the current directory without affecting its parent
       (and everyone else for that matter).

       Because native operating system filehandles are global and are currently allocated down
       from 255, with 0 being a reserved value, the Unix emulation library emulates Unix filehan-
       dles.  Consequently, you can't rely on passing "STDIN", "STDOUT", or "STDERR" to your
       children.

       The desire of users to express filenames of the form "<Foo$Dir>.Bar" on the command line
       unquoted causes problems, too: `` command output capture has to perform a guessing game.
       It assumes that a string "<[^<>]+\$[^<>]>" is a reference to an environment variable,
       whereas anything else involving "<" or ">" is redirection, and generally manages to be 99%
       right.  Of course, the problem remains that scripts cannot rely on any Unix tools being
       available, or that any tools found have Unix-like command line arguments.

       Extensions and XS are, in theory, buildable by anyone using free tools.	In practice, many
       don't, as users of the Acorn platform are used to binary distributions.	MakeMaker does
       run, but no available make currently copes with MakeMaker's makefiles; even if and when
       this should be fixed, the lack of a Unix-like shell will cause problems with makefile
       rules, especially lines of the form "cd sdbm && make all", and anything using quoting.

       "RISC OS" is the proper name for the operating system, but the value in $^O is "riscos"
       (because we don't like shouting).

       Other perls

       Perl has been ported to many platforms that do not fit into any of the categories listed
       above.  Some, such as AmigaOS, Atari MiNT, BeOS, HP MPE/iX, QNX, Plan 9, and VOS, have
       been well-integrated into the standard Perl source code kit.  You may need to see the
       ports/ directory on CPAN for information, and possibly binaries, for the likes of: aos,
       Atari ST, lynxos, riscos, Novell Netware, Tandem Guardian, etc.	(Yes, we know that some
       of these OSes may fall under the Unix category, but we are not a standards body.)

       Some approximate operating system names and their $^O values in the "OTHER" category
       include:

	   OS		 $^O	    $Config{'archname'}
	   ------------------------------------------
	   Amiga DOS	 amigaos    m68k-amigos
	   BeOS 	 beos
	   MPE/iX	 mpeix	    PA-RISC1.1

       See also:

       o   Amiga, README.amiga (installed as perlamiga).

       o   Atari, README.mint and Guido Flohr's web page http://stud.uni-sb.de/~gufl0000/

       o   Be OS, README.beos

       o   HP 300 MPE/iX, README.mpeix and Mark Bixby's web page http://www.bixby.org/mark/per-
	   lix.html

       o   A free perl5-based PERL.NLM for Novell Netware is available in precompiled binary and
	   source code form from http://www.novell.com/ as well as from CPAN.

       o   Plan 9, README.plan9

FUNCTION IMPLEMENTATIONS
       Listed below are functions that are either completely unimplemented or else have been
       implemented differently on various platforms.  Following each description will be, in
       parentheses, a list of platforms that the description applies to.

       The list may well be incomplete, or even wrong in some places.  When in doubt, consult the
       platform-specific README files in the Perl source distribution, and any other documenta-
       tion resources accompanying a given port.

       Be aware, moreover, that even among Unix-ish systems there are variations.

       For many functions, you can also query %Config, exported by default from the Config mod-
       ule.  For example, to check whether the platform has the "lstat" call, check $Con-
       fig{d_lstat}.  See Config for a full description of available variables.

       Alphabetical Listing of Perl Functions

       -X FILEHANDLE
       -X EXPR
       -X      "-r", "-w", and "-x" have a limited meaning only; directories and applications are
	       executable, and there are no uid/gid considerations.  "-o" is not supported.
	       (Mac OS)

	       "-r", "-w", "-x", and "-o" tell whether the file is accessible, which may not
	       reflect UIC-based file protections.  (VMS)

	       "-s" returns the size of the data fork, not the total size of data fork plus
	       resource fork.  (Mac OS).

	       "-s" by name on an open file will return the space reserved on disk, rather than
	       the current extent.  "-s" on an open filehandle returns the current size.
	       (RISC OS)

	       "-R", "-W", "-X", "-O" are indistinguishable from "-r", "-w", "-x", "-o". (Mac OS,
	       Win32, VMS, RISC OS)

	       "-b", "-c", "-k", "-g", "-p", "-u", "-A" are not implemented.  (Mac OS)

	       "-g", "-k", "-l", "-p", "-u", "-A" are not particularly meaningful.  (Win32, VMS,
	       RISC OS)

	       "-d" is true if passed a device spec without an explicit directory.  (VMS)

	       "-T" and "-B" are implemented, but might misclassify Mac text files with foreign
	       characters; this is the case will all platforms, but may affect Mac OS often.
	       (Mac OS)

	       "-x" (or "-X") determine if a file ends in one of the executable suffixes.  "-S"
	       is meaningless.	(Win32)

	       "-x" (or "-X") determine if a file has an executable file type.	(RISC OS)

       alarm SECONDS
       alarm   Not implemented. (Win32)

       binmode FILEHANDLE
	       Meaningless.  (Mac OS, RISC OS)

	       Reopens file and restores pointer; if function fails, underlying filehandle may be
	       closed, or pointer may be in a different position.  (VMS)

	       The value returned by "tell" may be affected after the call, and the filehandle
	       may be flushed. (Win32)

       chmod LIST
	       Only limited meaning.  Disabling/enabling write permission is mapped to lock-
	       ing/unlocking the file. (Mac OS)

	       Only good for changing "owner" read-write access, "group", and "other" bits are
	       meaningless. (Win32)

	       Only good for changing "owner" and "other" read-write access. (RISC OS)

	       Access permissions are mapped onto VOS access-control list changes. (VOS)

	       The actual permissions set depend on the value of the "CYGWIN" in the SYSTEM envi-
	       ronment settings.  (Cygwin)

       chown LIST
	       Not implemented. (Mac OS, Win32, Plan 9, RISC OS, VOS)

	       Does nothing, but won't fail. (Win32)

       chroot FILENAME
       chroot  Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS, VM/ESA)

       crypt PLAINTEXT,SALT
	       May not be available if library or source was not provided when building perl.
	       (Win32)

	       Not implemented. (VOS)

       dbmclose HASH
	       Not implemented. (VMS, Plan 9, VOS)

       dbmopen HASH,DBNAME,MODE
	       Not implemented. (VMS, Plan 9, VOS)

       dump LABEL
	       Not useful. (Mac OS, RISC OS)

	       Not implemented. (Win32)

	       Invokes VMS debugger. (VMS)

       exec LIST
	       Not implemented. (Mac OS)

	       Implemented via Spawn. (VM/ESA)

	       Does not automatically flush output handles on some platforms.  (SunOS, Solaris,
	       HP-UX)

       exit EXPR
       exit    Emulates UNIX exit() (which considers "exit 1" to indicate an error) by mapping
	       the 1 to SS$_ABORT(44).  This behavior may be overridden with the pragma "use
	       vmsish 'exit'".	As with the CRTL's exit() function, "exit 0" is also mapped to an
	       exit status of SS$_NORMAL(1); this mapping cannot be overridden.  Any other argu-
	       ment to exit() is used directly as Perl's exit status. (VMS)

       fcntl FILEHANDLE,FUNCTION,SCALAR
	       Not implemented. (Win32, VMS)

       flock FILEHANDLE,OPERATION
	       Not implemented (Mac OS, VMS, RISC OS, VOS).

	       Available only on Windows NT (not on Windows 95). (Win32)

       fork    Not implemented. (Mac OS, AmigaOS, RISC OS, VOS, VM/ESA, VMS)

	       Emulated using multiple interpreters.  See perlfork.  (Win32)

	       Does not automatically flush output handles on some platforms.  (SunOS, Solaris,
	       HP-UX)

       getlogin
	       Not implemented. (Mac OS, RISC OS)

       getpgrp PID
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       getppid Not implemented. (Mac OS, Win32, RISC OS)

       getpriority WHICH,WHO
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)

       getpwnam NAME
	       Not implemented. (Mac OS, Win32)

	       Not useful. (RISC OS)

       getgrnam NAME
	       Not implemented. (Mac OS, Win32, VMS, RISC OS)

       getnetbyname NAME
	       Not implemented. (Mac OS, Win32, Plan 9)

       getpwuid UID
	       Not implemented. (Mac OS, Win32)

	       Not useful. (RISC OS)

       getgrgid GID
	       Not implemented. (Mac OS, Win32, VMS, RISC OS)

       getnetbyaddr ADDR,ADDRTYPE
	       Not implemented. (Mac OS, Win32, Plan 9)

       getprotobynumber NUMBER
	       Not implemented. (Mac OS)

       getservbyport PORT,PROTO
	       Not implemented. (Mac OS)

       getpwent
	       Not implemented. (Mac OS, Win32, VM/ESA)

       getgrent
	       Not implemented. (Mac OS, Win32, VMS, VM/ESA)

       gethostent
	       Not implemented. (Mac OS, Win32)

       getnetent
	       Not implemented. (Mac OS, Win32, Plan 9)

       getprotoent
	       Not implemented. (Mac OS, Win32, Plan 9)

       getservent
	       Not implemented. (Win32, Plan 9)

       sethostent STAYOPEN
	       Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setnetent STAYOPEN
	       Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setprotoent STAYOPEN
	       Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setservent STAYOPEN
	       Not implemented. (Plan 9, Win32, RISC OS)

       endpwent
	       Not implemented. (Mac OS, MPE/iX, VM/ESA, Win32)

       endgrent
	       Not implemented. (Mac OS, MPE/iX, RISC OS, VM/ESA, VMS, Win32)

       endhostent
	       Not implemented. (Mac OS, Win32)

       endnetent
	       Not implemented. (Mac OS, Win32, Plan 9)

       endprotoent
	       Not implemented. (Mac OS, Win32, Plan 9)

       endservent
	       Not implemented. (Plan 9, Win32)

       getsockopt SOCKET,LEVEL,OPTNAME
	       Not implemented. (Plan 9)

       glob EXPR
       glob    This operator is implemented via the File::Glob extension on most platforms.  See
	       File::Glob for portability information.

       ioctl FILEHANDLE,FUNCTION,SCALAR
	       Not implemented. (VMS)

	       Available only for socket handles, and it does what the ioctlsocket() call in the
	       Winsock API does. (Win32)

	       Available only for socket handles. (RISC OS)

       kill SIGNAL, LIST
	       "kill(0, LIST)" is implemented for the sake of taint checking; use with other sig-
	       nals is unimplemented. (Mac OS)

	       Not implemented, hence not useful for taint checking. (RISC OS)

	       "kill()" doesn't have the semantics of "raise()", i.e. it doesn't send a signal to
	       the identified process like it does on Unix platforms.  Instead "kill($sig, $pid)"
	       terminates the process identified by $pid, and makes it exit immediately with exit
	       status $sig.  As in Unix, if $sig is 0 and the specified process exists, it
	       returns true without actually terminating it. (Win32)

       link OLDFILE,NEWFILE
	       Not implemented. (Mac OS, MPE/iX, VMS, RISC OS)

	       Link count not updated because hard links are not quite that hard (They are sort
	       of half-way between hard and soft links). (AmigaOS)

	       Hard links are implemented on Win32 (Windows NT and Windows 2000) under NTFS only.

       lstat FILEHANDLE
       lstat EXPR
       lstat   Not implemented. (VMS, RISC OS)

	       Return values (especially for device and inode) may be bogus. (Win32)

       msgctl ID,CMD,ARG
       msgget KEY,FLAGS
       msgsnd ID,MSG,FLAGS
       msgrcv ID,VAR,SIZE,TYPE,FLAGS
	       Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS)

       open FILEHANDLE,EXPR
       open FILEHANDLE
	       The "|" variants are supported only if ToolServer is installed.	(Mac OS)

	       open to "|-" and "-|" are unsupported. (Mac OS, Win32, RISC OS)

	       Opening a process does not automatically flush output handles on some platforms.
	       (SunOS, Solaris, HP-UX)

       pipe READHANDLE,WRITEHANDLE
	       Very limited functionality. (MiNT)

       readlink EXPR
       readlink
	       Not implemented. (Win32, VMS, RISC OS)

       select RBITS,WBITS,EBITS,TIMEOUT
	       Only implemented on sockets. (Win32, VMS)

	       Only reliable on sockets. (RISC OS)

	       Note that the "select FILEHANDLE" form is generally portable.

       semctl ID,SEMNUM,CMD,ARG
       semget KEY,NSEMS,FLAGS
       semop KEY,OPSTRING
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       setgrent
	       Not implemented. (Mac OS, MPE/iX, VMS, Win32, RISC OS)

       setpgrp PID,PGRP
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       setpriority WHICH,WHO,PRIORITY
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       setpwent
	       Not implemented. (Mac OS, MPE/iX, Win32, RISC OS)

       setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
	       Not implemented. (Plan 9)

       shmctl ID,CMD,ARG
       shmget KEY,SIZE,FLAGS
       shmread ID,VAR,POS,SIZE
       shmwrite ID,STRING,POS,SIZE
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       sockatmark SOCKET
	       A relatively recent addition to socket functions, may not be implemented even in
	       UNIX platforms.

       socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
	       Not implemented. (Win32, VMS, RISC OS, VOS, VM/ESA)

       stat FILEHANDLE
       stat EXPR
       stat    Platforms that do not have rdev, blksize, or blocks will return these as '', so
	       numeric comparison or manipulation of these fields may cause 'not numeric' warn-
	       ings.

	       mtime and atime are the same thing, and ctime is creation time instead of inode
	       change time. (Mac OS).

	       ctime not supported on UFS (Mac OS X).

	       ctime is creation time instead of inode change time  (Win32).

	       device and inode are not meaningful.  (Win32)

	       device and inode are not necessarily reliable.  (VMS)

	       mtime, atime and ctime all return the last modification time.  Device and inode
	       are not necessarily reliable.  (RISC OS)

	       dev, rdev, blksize, and blocks are not available.  inode is not meaningful and
	       will differ between stat calls on the same file.  (os2)

	       some versions of cygwin when doing a stat("foo") and if not finding it may then
	       attempt to stat("foo.exe") (Cygwin)

       symlink OLDFILE,NEWFILE
	       Not implemented. (Win32, VMS, RISC OS)

       syscall LIST
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)

       sysopen FILEHANDLE,FILENAME,MODE,PERMS
	       The traditional "0", "1", and "2" MODEs are implemented with different numeric
	       values on some systems.	The flags exported by "Fcntl" (O_RDONLY, O_WRONLY,
	       O_RDWR) should work everywhere though.  (Mac OS, OS/390, VM/ESA)

       system LIST
	       In general, do not assume the UNIX/POSIX semantics that you can shift $? right by
	       eight to get the exit value, or that "$? & 127" would give you the number of the
	       signal that terminated the program, or that "$? & 128" would test true if the pro-
	       gram was terminated by a coredump.  Instead, use the POSIX W*() interfaces: for
	       example, use WIFEXITED($?) and WEXITVALUE($?) to test for a normal exit and the
	       exit value, WIFSIGNALED($?) and WTERMSIG($?) for a signal exit and the signal.
	       Core dumping is not a portable concept, so there's no portable way to test for
	       that.

	       Only implemented if ToolServer is installed. (Mac OS)

	       As an optimization, may not call the command shell specified in $ENV{PERL5SHELL}.
	       "system(1, @args)" spawns an external process and immediately returns its process
	       designator, without waiting for it to terminate.  Return value may be used subse-
	       quently in "wait" or "waitpid".	Failure to spawn() a subprocess is indicated by
	       setting $? to "255 << 8".  $? is set in a way compatible with Unix (i.e. the exit-
	       status of the subprocess is obtained by "$? >> 8", as described in the documenta-
	       tion).  (Win32)

	       There is no shell to process metacharacters, and the native standard is to pass a
	       command line terminated by "\n" "\r" or "\0" to the spawned program.  Redirection
	       such as "> foo" is performed (if at all) by the run time library of the spawned
	       program.  "system" list will call the Unix emulation library's "exec" emulation,
	       which attempts to provide emulation of the stdin, stdout, stderr in force in the
	       parent, providing the child program uses a compatible version of the emulation
	       library.  scalar will call the native command line direct and no such emulation of
	       a child Unix program will exists.  Mileage will vary.  (RISC OS)

	       Far from being POSIX compliant.	Because there may be no underlying /bin/sh tries
	       to work around the problem by forking and execing the first token in its argument
	       string.	Handles basic redirection ("<" or ">") on its own behalf. (MiNT)

	       Does not automatically flush output handles on some platforms.  (SunOS, Solaris,
	       HP-UX)

	       The return value is POSIX-like (shifted up by 8 bits), which only allows room for
	       a made-up value derived from the severity bits of the native 32-bit condition code
	       (unless overridden by "use vmsish 'status'").  For more details see "$?" in per-
	       lvms. (VMS)

       times   Only the first entry returned is nonzero. (Mac OS)

	       "cumulative" times will be bogus.  On anything other than Windows NT or Windows
	       2000, "system" time will be bogus, and "user" time is actually the time returned
	       by the clock() function in the C runtime library. (Win32)

	       Not useful. (RISC OS)

       truncate FILEHANDLE,LENGTH
       truncate EXPR,LENGTH
	       Not implemented. (Older versions of VMS)

	       Truncation to zero-length only. (VOS)

	       If a FILEHANDLE is supplied, it must be writable and opened in append mode (i.e.,
	       use "open(FH, '>>filename')" or "sysopen(FH,...,O_APPEND|O_RDWR)".  If a filename
	       is supplied, it should not be held open elsewhere. (Win32)

       umask EXPR
       umask   Returns undef where unavailable, as of version 5.005.

	       "umask" works but the correct permissions are set only when the file is finally
	       closed. (AmigaOS)

       utime LIST
	       Only the modification time is updated. (BeOS, Mac OS, VMS, RISC OS)

	       May not behave as expected.  Behavior depends on the C runtime library's implemen-
	       tation of utime(), and the filesystem being used.  The FAT filesystem typically
	       does not support an "access time" field, and it may limit timestamps to a granu-
	       larity of two seconds. (Win32)

       wait
       waitpid PID,FLAGS
	       Not implemented. (Mac OS, VOS)

	       Can only be applied to process handles returned for processes spawned using "sys-
	       tem(1, ...)" or pseudo processes created with "fork()". (Win32)

	       Not useful. (RISC OS)

CHANGES
       v1.48, 02 February 2001
	   Various updates from perl5-porters over the past year, supported platforms update from
	   Jarkko Hietaniemi.

       v1.47, 22 March 2000
	   Various cleanups from Tom Christiansen, including migration of long platform listings
	   from perl.

       v1.46, 12 February 2000
	   Updates for VOS and MPE/iX. (Peter Prymmer)	Other small changes.

       v1.45, 20 December 1999
	   Small changes from 5.005_63 distribution, more changes to EBCDIC info.

       v1.44, 19 July 1999
	   A bunch of updates from Peter Prymmer for $^O values, endianness, File::Spec, VMS,
	   BS2000, OS/400.

       v1.43, 24 May 1999
	   Added a lot of cleaning up from Tom Christiansen.

       v1.42, 22 May 1999
	   Added notes about tests, sprintf/printf, and epoch offsets.

       v1.41, 19 May 1999
	   Lots more little changes to formatting and content.

	   Added a bunch of $^O and related values for various platforms; fixed mail and web
	   addresses, and added and changed miscellaneous notes.  (Peter Prymmer)

       v1.40, 11 April 1999
	   Miscellaneous changes.

       v1.39, 11 February 1999
	   Changes from Jarkko and EMX URL fixes Michael Schwern.  Additional note about newlines
	   added.

       v1.38, 31 December 1998
	   More changes from Jarkko.

       v1.37, 19 December 1998
	   More minor changes.	Merge two separate version 1.35 documents.

       v1.36, 9 September 1998
	   Updated for Stratus VOS.  Also known as version 1.35.

       v1.35, 13 August 1998
	   Integrate more minor changes, plus addition of new sections under "ISSUES": "Numbers
	   endianness and Width", "Character sets and character encoding", "Internationalisa-
	   tion".

       v1.33, 06 August 1998
	   Integrate more minor changes.

       v1.32, 05 August 1998
	   Integrate more minor changes.

       v1.30, 03 August 1998
	   Major update for RISC OS, other minor changes.

       v1.23, 10 July 1998
	   First public release with perl5.005.

Supported Platforms
       As of July 2002 (the Perl release 5.8.0), the following platforms are able to build Perl
       from the standard source code distribution available at http://www.cpan.org/src/index.html

	       AIX
	       BeOS
	       Cygwin
	       DG/UX
	       DOS DJGPP       1)
	       DYNIX/ptx
	       EPOC R5
	       FreeBSD
	       HP-UX
	       IRIX
	       Linux
	       Mac OS Classic
	       Mac OS X 	(Darwin)
	       MPE/iX
	       NetBSD
	       NetWare
	       NonStop-UX
	       ReliantUNIX     (SINIX)
	       OpenBSD
	       OpenVMS	       (VMS)
	       OS/2
	       OS/400	       (using the PASE) (since Perl 5.8.1/5.9.0)
	       PowerUX
	       POSIX-BC        (BS2000)
	       QNX
	       Solaris
	       SunOS 4
	       SUPER-UX
	       Tru64 UNIX      (DEC OSF/1, Digital UNIX)
	       UNICOS
	       UNICOS/mk
	       UTS
	       VOS
	       Win95/98/ME/2K/XP 2)
	       WinCE
	       z/OS	       (OS/390)
	       VM/ESA

	       1) in DOS mode either the DOS or OS/2 ports can be used
	       2) compilers: Borland, MinGW (GCC), VC6

       The following platforms worked with the previous releases (5.6 and 5.7), but we did not
       manage either to fix or to test these in time for the 5.8.0 release.  There is a very good
       chance that many of these will work fine with the 5.8.0.

	       BSD/OS
	       DomainOS
	       Hurd
	       LynxOS
	       MachTen
	       PowerMAX
	       SCO SV
	       SVR4
	       Unixware
	       Windows 3.1

       Known to be broken for 5.8.0 (but 5.6.1 and 5.7.2 can be used):

	       AmigaOS

       The following platforms have been known to build Perl from source in the past (5.005_03
       and earlier), but we haven't been able to verify their status for the current release,
       either because the hardware/software platforms are rare or because we don't have an active
       champion on these platforms--or both.  They used to work, though, so go ahead and try com-
       piling them, and let perlbug@perl.org of any trouble.

	       3b1
	       A/UX
	       ConvexOS
	       CX/UX
	       DC/OSx
	       DDE SMES
	       DOS EMX
	       Dynix
	       EP/IX
	       ESIX
	       FPS
	       GENIX
	       Greenhills
	       ISC
	       MachTen 68k
	       MiNT
	       MPC
	       NEWS-OS
	       NextSTEP
	       OpenSTEP
	       Opus
	       Plan 9
	       RISC/os
	       SCO ODT/OSR
	       Stellar
	       SVR2
	       TI1500
	       TitanOS
	       Ultrix
	       Unisys Dynix

       The following platforms have their own source code distributions and binaries available
       via http://www.cpan.org/ports/

				       Perl release

	       OS/400 (ILE)	       5.005_02
	       Tandem Guardian	       5.004

       The following platforms have only binaries available via
       http://www.cpan.org/ports/index.html :

				       Perl release

	       Acorn RISCOS	       5.005_02
	       AOS		       5.002
	       LynxOS		       5.004_02

       Although we do suggest that you always build your own Perl from the source code, both for
       maximal configurability and for security, in case you are in a hurry you can check
       http://www.cpan.org/ports/index.html for binary distributions.

SEE ALSO
       perlaix, perlamiga, perlapollo, perlbeos, perlbs2000, perlce, perlcygwin, perldgux, perl-
       dos, perlepoc, perlebcdic, perlfreebsd, perlhurd, perlhpux, perlirix, perlmachten, perlma-
       cos, perlmint, perlmpeix, perlnetware, perlos2, perlos390, perlos400, perlplan9, perlqnx,
       perlsolaris, perltru64, perlunicode, perlvmesa, perlvms, perlvos, perlwin32, and Win32.

AUTHORS / CONTRIBUTORS
       Abigail <abigail@foad.org>, Charles Bailey <bailey@newman.upenn.edu>, Graham Barr
       <gbarr@pobox.com>, Tom Christiansen <tchrist@perl.com>, Nicholas Clark <nick@ccl4.org>,
       Thomas Dorner <Thomas.Dorner@start.de>, Andy Dougherty <doughera@lafayette.edu>, Dominic
       Dunlop <domo@computer.org>, Neale Ferguson <neale@vma.tabnsw.com.au>, David J. Fiander
       <davidf@mks.com>, Paul Green <Paul_Green@stratus.com>, M.J.T. Guy <mjtg@cam.ac.uk>, Jarkko
       Hietaniemi <jhi@iki.fi>, Luther Huffman <lutherh@stratcom.com>, Nick Ing-Simmons
       <nick@ing-simmons.net>, Andreas J. Koenig <a.koenig@mind.de>, Markus Laker <mlaker@con-
       tax.co.uk>, Andrew M. Langmead <aml@world.std.com>, Larry Moore <ljmoore@freespace.net>,
       Paul Moore <Paul.Moore@uk.origin-it.com>, Chris Nandor <pudge@pobox.com>, Matthias Neer-
       acher <neeracher@mac.com>, Philip Newton <pne@cpan.org>, Gary Ng <71564.1743@Com-
       puServe.COM>, Tom Phoenix <rootbeer@teleport.com>, Andre Pirard <A.Pirard@ulg.ac.be>,
       Peter Prymmer <pvhp@forte.com>, Hugo van der Sanden <hv@crypt0.demon.co.uk>, Gurusamy
       Sarathy <gsar@activestate.com>, Paul J. Schinder <schinder@pobox.com>, Michael G Schwern
       <schwern@pobox.com>, Dan Sugalski <dan@sidhe.org>, Nathan Torkington <gnat@frii.com>.

perl v5.8.0				    2003-02-18				      PERLPORT(1)


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