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

PERLVMS(1)			 Perl Programmers Reference Guide		       PERLVMS(1)

NAME
       perlvms - VMS-specific documentation for Perl

DESCRIPTION
       Gathered below are notes describing details of Perl 5's behavior on VMS.  They are a sup-
       plement to the regular Perl 5 documentation, so we have focussed on the ways in which Perl
       5 functions differently under VMS than it does under Unix, and on the interactions between
       Perl and the rest of the operating system.  We haven't tried to duplicate complete
       descriptions of Perl features from the main Perl documentation, which can be found in the
       [.pod] subdirectory of the Perl distribution.

       We hope these notes will save you from confusion and lost sleep when writing Perl scripts
       on VMS.	If you find we've missed something you think should appear here, please don't
       hesitate to drop a line to vmsperl@perl.org.

Installation
       Directions for building and installing Perl 5 can be found in the file README.vms in the
       main source directory of the Perl distribution..

Organization of Perl Images
       Core Images

       During the installation process, three Perl images are produced.  Miniperl.Exe is an exe-
       cutable image which contains all of the basic functionality of Perl, but cannot take
       advantage of Perl extensions.  It is used to generate several files needed to build the
       complete Perl and various extensions.  Once you've finished installing Perl, you can
       delete this image.

       Most of the complete Perl resides in the shareable image PerlShr.Exe, which provides a
       core to which the Perl executable image and all Perl extensions are linked.  You should
       place this image in Sys$Share, or define the logical name PerlShr to translate to the full
       file specification of this image.  It should be world readable.	(Remember that if a user
       has execute only access to PerlShr, VMS will treat it as if it were a privileged shareable
       image, and will therefore require all downstream shareable images to be INSTALLed, etc.)

       Finally, Perl.Exe is an executable image containing the main entry point for Perl, as well
       as some initialization code.  It should be placed in a public directory, and made world
       executable.  In order to run Perl with command line arguments, you should define a foreign
       command to invoke this image.

       Perl Extensions

       Perl extensions are packages which provide both XS and Perl code to add new functionality
       to perl.  (XS is a meta-language which simplifies writing C code which interacts with
       Perl, see perlxs for more details.)  The Perl code for an extension is treated like any
       other library module - it's made available in your script through the appropriate "use" or
       "require" statement, and usually defines a Perl package containing the extension.

       The portion of the extension provided by the XS code may be connected to the rest of Perl
       in either of two ways.  In the static configuration, the object code for the extension is
       linked directly into PerlShr.Exe, and is initialized whenever Perl is invoked.  In the
       dynamic configuration, the extension's machine code is placed into a separate shareable
       image, which is mapped by Perl's DynaLoader when the extension is "use"d or "require"d in
       your script.  This allows you to maintain the extension as a separate entity, at the cost
       of keeping track of the additional shareable image.  Most extensions can be set up as
       either static or dynamic.

       The source code for an extension usually resides in its own directory.  At least three
       files are generally provided: Extshortname.xs (where Extshortname is the portion of the
       extension's name following the last "::"), containing the XS code, Extshortname.pm, the
       Perl library module for the extension, and Makefile.PL, a Perl script which uses the
       "MakeMaker" library modules supplied with Perl to generate a Descrip.MMS file for the
       extension.

       Installing static extensions

       Since static extensions are incorporated directly into PerlShr.Exe, you'll have to rebuild
       Perl to incorporate a new extension.  You should edit the main Descrip.MMS or Makefile you
       use to build Perl, adding the extension's name to the "ext" macro, and the extension's
       object file to the "extobj" macro.  You'll also need to build the extension's object file,
       either by adding dependencies to the main Descrip.MMS, or using a separate Descrip.MMS for
       the extension.  Then, rebuild PerlShr.Exe to incorporate the new code.

       Finally, you'll need to copy the extension's Perl library module to the [.Extname] subdi-
       rectory under one of the directories in @INC, where Extname is the name of the extension,
       with all "::" replaced by "." (e.g.  the library module for extension Foo::Bar would be
       copied to a [.Foo.Bar] subdirectory).

       Installing dynamic extensions

       In general, the distributed kit for a Perl extension includes a file named Makefile.PL,
       which is a Perl program which is used to create a Descrip.MMS file which can be used to
       build and install the files required by the extension.  The kit should be unpacked into a
       directory tree not under the main Perl source directory, and the procedure for building
       the extension is simply

	   $ perl Makefile.PL  ! Create Descrip.MMS
	   $ mmk	       ! Build necessary files
	   $ mmk test	       ! Run test code, if supplied
	   $ mmk install       ! Install into public Perl tree

       N.B. The procedure by which extensions are built and tested creates several levels (at
       least 4) under the directory in which the extension's source files live.  For this reason,
       you shouldn't nest the source directory too deeply in your directory structure, lest you
       exceed RMS' maximum of 8 levels of subdirectory in a filespec.  (You can use rooted logi-
       cal names to get another 8 levels of nesting, if you can't place the files near the top of
       the physical directory structure.)

       VMS support for this process in the current release of Perl is sufficient to handle most
       extensions.  However, it does not yet recognize extra libraries required to build share-
       able images which are part of an extension, so these must be added to the linker options
       file for the extension by hand.	For instance, if the PGPLOT extension to Perl requires
       the PGPLOTSHR.EXE shareable image in order to properly link the Perl extension, then the
       line "PGPLOTSHR/Share" must be added to the linker options file PGPLOT.Opt produced during
       the build process for the Perl extension.

       By default, the shareable image for an extension is placed
       [.lib.site_perl.autoArch.Extname] directory of the installed Perl directory tree (where
       Arch is VMS_VAX or VMS_AXP, and Extname is the name of the extension, with each "::"
       translated to ".").  (See the MakeMaker documentation for more details on installation
       options for extensions.)  However, it can be manually placed in any of several locations:
	  - the [.Lib.Auto.Arch$PVersExtname] subdirectory
	    of one of the directories in @INC (where PVers
	    is the version of Perl you're using, as supplied in $],
	    with '.' converted to '_'), or
	  - one of the directories in @INC, or
	  - a directory which the extensions Perl library module
	    passes to the DynaLoader when asking it to map
	    the shareable image, or
	  - Sys$Share or Sys$Library.  If the shareable image isn't in any of these places,
       you'll need to define a logical name Extshortname, where Extshortname is the portion of
       the extension's name after the last "::", which translates to the full file specification
       of the shareable image.

File specifications
       Syntax

       We have tried to make Perl aware of both VMS-style and Unix- style file specifications
       wherever possible.  You may use either style, or both, on the command line and in scripts,
       but you may not combine the two styles within a single file specification.  VMS Perl
       interprets Unix pathnames in much the same way as the CRTL (e.g. the first component of an
       absolute path is read as the device name for the VMS file specification).  There are a set
       of functions provided in the "VMS::Filespec" package for explicit interconversion between
       VMS and Unix syntax; its documentation provides more details.

       Filenames are, of course, still case-insensitive.  For consistency, most Perl routines
       return  filespecs using lower case letters only, regardless of the case used in the argu-
       ments passed to them.  (This is true  only when running under VMS; Perl respects the case-
       sensitivity of OSs like Unix.)

       We've tried to minimize the dependence of Perl library modules on Unix syntax, but you may
       find that some of these, as well as some scripts written for Unix systems, will require
       that you use Unix syntax, since they will assume that '/' is the directory separator, etc.
       If you find instances of this in the Perl distribution itself, please let us know, so we
       can try to work around them.

       Wildcard expansion

       File specifications containing wildcards are allowed both on the command line and within
       Perl globs (e.g. "<*.c>").  If the wildcard filespec uses VMS syntax, the resultant file-
       specs will follow VMS syntax; if a Unix-style filespec is passed in, Unix-style filespecs
       will be returned.

       In both cases, VMS wildcard expansion is performed. (csh-style wildcard expansion is
       available if you use "File::Glob::glob".)  If the wildcard filespec contains a device or
       directory specification, then the resultant filespecs will also contain a device and
       directory; otherwise, device and directory information are removed.  VMS-style resultant
       filespecs will contain a full device and directory, while Unix-style resultant filespecs
       will contain only as much of a directory path as was present in the input filespec.  For
       example, if your default directory is Perl_Root:[000000], the expansion of "[.t]*.*" will
       yield filespecs	like "perl_root:[t]base.dir", while the expansion of "t/*/*" will yield
       filespecs like "t/base.dir".  (This is done to match the behavior of glob expansion per-
       formed by Unix shells.)

       Similarly, the resultant filespec will contain the file version only if one was present in
       the input filespec.

       Pipes

       Input and output pipes to Perl filehandles are supported; the "file name" is passed to
       lib$spawn() for asynchronous execution.	You should be careful to close any pipes you have
       opened in a Perl script, lest you leave any "orphaned" subprocesses around when Perl
       exits.

       You may also use backticks to invoke a DCL subprocess, whose output is used as the return
       value of the expression.  The string between the backticks is handled as if it were the
       argument to the "system" operator (see below).  In this case, Perl will wait for the sub-
       process to complete before continuing.

       The mailbox (MBX) that perl can create to communicate with a pipe defaults to a buffer
       size of 512.  The default buffer size is adjustable via the logical name PERL_MBX_SIZE
       provided that the value falls between 128 and the SYSGEN parameter MAXBUF inclusive.  For
       example, to double the MBX size from the default within a Perl program, use
       "$ENV{'PERL_MBX_SIZE'} = 1024;" and then open and use pipe constructs.  An alternative
       would be to issue the command:

	   $ Define PERL_MBX_SIZE 1024

       before running your wide record pipe program.  A larger value may improve performance at
       the expense of the BYTLM UAF quota.

PERL5LIB and PERLLIB
       The PERL5LIB and PERLLIB logical names work as documented in perl, except that the element
       separator is '|' instead of ':'.  The directory specifications may use either VMS or Unix
       syntax.

Command line
       I/O redirection and backgrounding

       Perl for VMS supports redirection of input and output on the command line, using a subset
       of Bourne shell syntax:

       o   "<file" reads stdin from "file",

       o   ">file" writes stdout to "file",

       o   ">>file" appends stdout to "file",

       o   "2>file" writes stderr to "file", and

       o   "2>>file" appends stderr to "file".

       In addition, output may be piped to a subprocess, using the character '|'.  Anything after
       this character on the command line is passed to a subprocess for execution; the subprocess
       takes the output of Perl as its input.

       Finally, if the command line ends with '&', the entire command is run in the background as
       an asynchronous subprocess.

       Command line switches

       The following command line switches behave differently under VMS than described in perl-
       run.  Note also that in order to pass uppercase switches to Perl, you need to enclose them
       in double-quotes on the command line, since the CRTL downcases all unquoted strings.

       -i  If the "-i" switch is present but no extension for a backup copy is given, then
	   inplace editing creates a new version of a file; the existing copy is not deleted.
	   (Note that if an extension is given, an existing file is renamed to the backup file,
	   as is the case under other operating systems, so it does not remain as a previous ver-
	   sion under the original filename.)

       -S  If the "-S" or "-"S"" switch is present and the script name does not contain a direc-
	   tory, then Perl translates the logical name DCL$PATH as a searchlist, using each
	   translation as a directory in which to look for the script.	In addition, if no file
	   type is specified, Perl looks in each directory for a file matching the name speci-
	   fied, with a blank type, a type of .pl, and a type of .com, in that order.

       -u  The "-u" switch causes the VMS debugger to be invoked after the Perl program is com-
	   piled, but before it has run.  It does not create a core dump file.

Perl functions
       As of the time this document was last revised, the following Perl functions were imple-
       mented in the VMS port of Perl (functions marked with * are discussed in more detail
       below):

	   file tests*, abs, alarm, atan, backticks*, binmode*, bless,
	   caller, chdir, chmod, chown, chomp, chop, chr,
	   close, closedir, cos, crypt*, defined, delete,
	   die, do, dump*, each, endpwent, eof, eval, exec*,
	   exists, exit, exp, fileno, getc, getlogin, getppid,
	   getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
	   grep, hex, import, index, int, join, keys, kill*,
	   last, lc, lcfirst, length, local, localtime, log, m//,
	   map, mkdir, my, next, no, oct, open, opendir, ord, pack,
	   pipe, pop, pos, print, printf, push, q//, qq//, qw//,
	   qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
	   require, reset, return, reverse, rewinddir, rindex,
	   rmdir, s///, scalar, seek, seekdir, select(internal),
	   select (system call)*, setpwent, shift, sin, sleep,
	   sort, splice, split, sprintf, sqrt, srand, stat,
	   study, substr, sysread, system*, syswrite, tell,
	   telldir, tie, time, times*, tr///, uc, ucfirst, umask,
	   undef, unlink*, unpack, untie, unshift, use, utime*,
	   values, vec, wait, waitpid*, wantarray, warn, write, y///

       The following functions were not implemented in the VMS port, and calling them produces a
       fatal error (usually) or undefined behavior (rarely, we hope):

	   chroot, dbmclose, dbmopen, flock, fork*,
	   getpgrp, getpriority, getgrent, getgrgid,
	   getgrnam, setgrent, endgrent, ioctl, link, lstat,
	   msgctl, msgget, msgsend, msgrcv, readlink, semctl,
	   semget, semop, setpgrp, setpriority, shmctl, shmget,
	   shmread, shmwrite, socketpair, symlink, syscall

       The following functions are available on Perls compiled with Dec C 5.2 or greater and run-
       ning VMS 7.0 or greater:

	   truncate

       The following functions are available on Perls built on VMS 7.2 or greater:

	   fcntl (without locking)

       The following functions may or may not be implemented, depending on what type of socket
       support you've built into your copy of Perl:

	   accept, bind, connect, getpeername,
	   gethostbyname, getnetbyname, getprotobyname,
	   getservbyname, gethostbyaddr, getnetbyaddr,
	   getprotobynumber, getservbyport, gethostent,
	   getnetent, getprotoent, getservent, sethostent,
	   setnetent, setprotoent, setservent, endhostent,
	   endnetent, endprotoent, endservent, getsockname,
	   getsockopt, listen, recv, select(system call)*,
	   send, setsockopt, shutdown, socket

       File tests
	   The tests "-b", "-B", "-c", "-C", "-d", "-e", "-f", "-o", "-M", "-s", "-S", "-t",
	   "-T", and "-z" work as advertised.  The return values for "-r", "-w", and "-x" tell
	   you whether you can actually access the file; this may not reflect the UIC-based file
	   protections.  Since real and effective UIC don't differ under VMS, "-O", "-R", "-W",
	   and "-X" are equivalent to "-o", "-r", "-w", and "-x".  Similarly, several other
	   tests, including "-A", "-g", "-k", "-l", "-p", and "-u", aren't particularly meaning-
	   ful under VMS, and the values returned by these tests reflect whatever your CRTL
	   "stat()" routine does to the equivalent bits in the st_mode field.  Finally, "-d"
	   returns true if passed a device specification without an explicit directory (e.g.
	   "DUA1:"), as well as if passed a directory.

	   Note: Some sites have reported problems when using the file-access tests ("-r", "-w",
	   and "-x") on files accessed via DEC's DFS.  Specifically, since DFS does not currently
	   provide access to the extended file header of files on remote volumes, attempts to
	   examine the ACL fail, and the file tests will return false, with $! indicating that
	   the file does not exist.  You can use "stat" on these files, since that checks UIC-
	   based protection only, and then manually check the appropriate bits, as defined by
	   your C compiler's stat.h, in the mode value it returns, if you need an approximation
	   of the file's protections.

       backticks
	   Backticks create a subprocess, and pass the enclosed string to it for execution as a
	   DCL command.  Since the subprocess is created directly via "lib$spawn()", any valid
	   DCL command string may be specified.

       binmode FILEHANDLE
	   The "binmode" operator will attempt to insure that no translation of carriage control
	   occurs on input from or output to this filehandle.  Since this involves reopening the
	   file and then restoring its file position indicator, if this function returns FALSE,
	   the underlying filehandle may no longer point to an open file, or may point to a dif-
	   ferent position in the file than before "binmode" was called.

	   Note that "binmode" is generally not necessary when using normal filehandles; it is
	   provided so that you can control I/O to existing record-structured files when neces-
	   sary.  You can also use the "vmsfopen" function in the VMS::Stdio extension to gain
	   finer control of I/O to files and devices with different record structures.

       crypt PLAINTEXT, USER
	   The "crypt" operator uses the "sys$hash_password" system service to generate the
	   hashed representation of PLAINTEXT.	If USER is a valid username, the algorithm and
	   salt values are taken from that user's UAF record.  If it is not, then the preferred
	   algorithm and a salt of 0 are used.	The quadword encrypted value is returned as an
	   8-character string.

	   The value returned by "crypt" may be compared against the encrypted password from the
	   UAF returned by the "getpw*" functions, in order to authenticate users.  If you're
	   going to do this, remember that the encrypted password in the UAF was generated using
	   uppercase username and password strings; you'll have to upcase the arguments to
	   "crypt" to insure that you'll get the proper value:

	       sub validate_passwd {
		   my($user,$passwd) = @_;
		   my($pwdhash);
		   if ( !($pwdhash = (getpwnam($user))[1]) ||
			  $pwdhash ne crypt("\U$passwd","\U$name") ) {
		       intruder_alert($name);
		   }
		   return 1;
	       }

       dump
	   Rather than causing Perl to abort and dump core, the "dump" operator invokes the VMS
	   debugger.  If you continue to execute the Perl program under the debugger, control
	   will be transferred to the label specified as the argument to "dump", or, if no label
	   was specified, back to the beginning of the program.  All other state of the program
	   (e.g. values of variables, open file handles) are not affected by calling "dump".

       exec LIST
	   A call to "exec" will cause Perl to exit, and to invoke the command given as an argu-
	   ment to "exec" via "lib$do_command".  If the argument begins with '@' or '$' (other
	   than as part of a filespec), then it is executed as a DCL command.  Otherwise, the
	   first token on the command line is treated as the filespec of an image to run, and an
	   attempt is made to invoke it (using .Exe and the process defaults to expand the file-
	   spec) and pass the rest of "exec"'s argument to it as parameters.  If the token has no
	   file type, and matches a file with null type, then an attempt is made to determine
	   whether the file is an executable image which should be invoked using "MCR" or a text
	   file which should be passed to DCL as a command procedure.

       fork
	   While in principle the "fork" operator could be implemented via (and with the same
	   rather severe limitations as) the CRTL "vfork()" routine, and while some internal sup-
	   port to do just that is in place, the implementation has never been completed, making
	   "fork" currently unavailable.  A true kernel "fork()" is expected in a future version
	   of VMS, and the pseudo-fork based on interpreter threads may be available in a future
	   version of Perl on VMS (see perlfork).  In the meantime, use "system", backticks, or
	   piped filehandles to create subprocesses.

       getpwent
       getpwnam
       getpwuid
	   These operators obtain the information described in perlfunc, if you have the privi-
	   leges necessary to retrieve the named user's UAF information via "sys$getuai".  If
	   not, then only the $name, $uid, and $gid items are returned.  The $dir item contains
	   the login directory in VMS syntax, while the $comment item contains the login direc-
	   tory in Unix syntax. The $gcos item contains the owner field from the UAF record.  The
	   $quota item is not used.

       gmtime
	   The "gmtime" operator will function properly if you have a working CRTL "gmtime()"
	   routine, or if the logical name SYS$TIMEZONE_DIFFERENTIAL is defined as the number of
	   seconds which must be added to UTC to yield local time.  (This logical name is defined
	   automatically if you are running a version of VMS with built-in UTC support.)  If nei-
	   ther of these cases is true, a warning message is printed, and "undef" is returned.

       kill
	   In most cases, "kill" is implemented via the CRTL's "kill()" function, so it will
	   behave according to that function's documentation.  If you send a SIGKILL, however,
	   the $DELPRC system service is called directly.  This insures that the target process
	   is actually deleted, if at all possible.  (The CRTL's "kill()" function is presently
	   implemented via $FORCEX, which is ignored by supervisor-mode images like DCL.)

	   Also, negative signal values don't do anything special under VMS; they're just con-
	   verted to the corresponding positive value.

       qx//
	   See the entry on "backticks" above.

       select (system call)
	   If Perl was not built with socket support, the system call version of "select" is not
	   available at all.  If socket support is present, then the system call version of
	   "select" functions only for file descriptors attached to sockets.  It will not provide
	   information about regular files or pipes, since the CRTL "select()" routine does not
	   provide this functionality.

       stat EXPR
	   Since VMS keeps track of files according to a different scheme than Unix, it's not
	   really possible to represent the file's ID in the "st_dev" and "st_ino" fields of a
	   "struct stat".  Perl tries its best, though, and the values it uses are pretty
	   unlikely to be the same for two different files.  We can't guarantee this, though, so
	   caveat scriptor.

       system LIST
	   The "system" operator creates a subprocess, and passes its arguments to the subprocess
	   for execution as a DCL command.  Since the subprocess is created directly via
	   "lib$spawn()", any valid DCL command string may be specified.  If the string begins
	   with '@', it is treated as a DCL command unconditionally.  Otherwise, if the first
	   token contains a character used as a delimiter in file specification (e.g. ":" or
	   "]"), an attempt is made to expand it using	a default type of .Exe and the process
	   defaults, and if successful, the resulting file is invoked via "MCR". This allows you
	   to invoke an image directly simply by passing the file specification to "system", a
	   common Unixish idiom.  If the token has no file type, and matches a file with null
	   type, then an attempt is made to determine whether the file is an executable image
	   which should be invoked using "MCR" or a text file which should be passed to DCL as a
	   command procedure.

	   If LIST consists of the empty string, "system" spawns an interactive DCL subprocess,
	   in the same fashion as typing SPAWN at the DCL prompt.

	   Perl waits for the subprocess to complete before continuing execution in the current
	   process.  As described in perlfunc, the return value of "system" is a fake "status"
	   which follows POSIX semantics unless the pragma "use vmsish 'status'" is in effect;
	   see the description of $? in this document for more detail.

       time
	   The value returned by "time" is the offset in seconds from 01-JAN-1970 00:00:00 (just
	   like the CRTL's times() routine), in order to make life easier for code coming in from
	   the POSIX/Unix world.

       times
	   The array returned by the "times" operator is divided up according to the same rules
	   the CRTL "times()" routine.	Therefore, the "system time" elements will always be 0,
	   since there is no difference between "user time" and "system" time under VMS, and the
	   time accumulated by a subprocess may or may not appear separately in the "child time"
	   field, depending on whether times keeps track of subprocesses separately.  Note espe-
	   cially that the VAXCRTL (at least) keeps track only of subprocesses spawned using fork
	   and exec; it will not accumulate the times of subprocesses spawned via pipes, system,
	   or backticks.

       unlink LIST
	   "unlink" will delete the highest version of a file only; in order to delete all ver-
	   sions, you need to say

	       1 while unlink LIST;

	   You may need to make this change to scripts written for a Unix system which expect
	   that after a call to "unlink", no files with the names passed to "unlink" will exist.
	   (Note: This can be changed at compile time; if you "use Config" and $Con-
	   fig{'d_unlink_all_versions'} is "define", then "unlink" will delete all versions of a
	   file on the first call.)

	   "unlink" will delete a file if at all possible, even if it requires changing file pro-
	   tection (though it won't try to change the protection of the parent directory).  You
	   can tell whether you've got explicit delete access to a file by using the "VMS::File-
	   spec::candelete" operator.  For instance, in order to delete only files to which you
	   have delete access, you could say something like

	       sub safe_unlink {
		   my($file,$num);
		   foreach $file (@_) {
		       next unless VMS::Filespec::candelete($file);
		       $num += unlink $file;
		   }
		   $num;
	       }

	   (or you could just use "VMS::Stdio::remove", if you've installed the VMS::Stdio exten-
	   sion distributed with Perl). If "unlink" has to change the file protection to delete
	   the file, and you interrupt it in midstream, the file may be left intact, but with a
	   changed ACL allowing you delete access.

       utime LIST
	   Since ODS-2, the VMS file structure for disk files, does not keep track of access
	   times, this operator changes only the modification time of the file (VMS revision
	   date).

       waitpid PID,FLAGS
	   If PID is a subprocess started by a piped "open()" (see open), "waitpid" will wait for
	   that subprocess, and return its final status value in $?.  If PID is a subprocess cre-
	   ated in some other way (e.g.  SPAWNed before Perl was invoked), "waitpid" will simply
	   check once per second whether the process has completed, and return when it has.  (If
	   PID specifies a process that isn't a subprocess of the current process, and you
	   invoked Perl with the "-w" switch, a warning will be issued.)

	   Returns PID on success, -1 on error.  The FLAGS argument is ignored in all cases.

Perl variables
       The following VMS-specific information applies to the indicated "special" Perl variables,
       in addition to the general information in perlvar.  Where there is a conflict, this infor-
       mation takes precedence.

       %ENV
	   The operation of the %ENV array depends on the translation of the logical name
	   PERL_ENV_TABLES.  If defined, it should be a search list, each element of which speci-
	   fies a location for %ENV elements.  If you tell Perl to read or set the element
	   "$ENV{"name"}", then Perl uses the translations of PERL_ENV_TABLES as follows:

	   CRTL_ENV
	       This string tells Perl to consult the CRTL's internal "environ" array of key-value
	       pairs, using name as the key.  In most cases, this contains only a few keys, but
	       if Perl was invoked via the C "exec[lv]e()" function, as is the case for CGI pro-
	       cessing by some HTTP servers, then the "environ" array may have been populated by
	       the calling program.

	   CLISYM_[LOCAL]
	       A string beginning with "CLISYM_"tells Perl to consult the CLI's symbol tables,
	       using name as the name of the symbol.  When reading an element of %ENV, the local
	       symbol table is scanned first, followed by the global symbol table..  The charac-
	       ters following "CLISYM_" are significant when an element of %ENV is set or
	       deleted: if the complete string is "CLISYM_LOCAL", the change is made in the local
	       symbol table; otherwise the global symbol table is changed.

	   Any other string
	       If an element of PERL_ENV_TABLES translates to any other string, that string is
	       used as the name of a logical name table, which is consulted using name as the
	       logical name.  The normal search order of access modes is used.

	   PERL_ENV_TABLES is translated once when Perl starts up; any changes you make while
	   Perl is running do not affect the behavior of %ENV.	If PERL_ENV_TABLES is not
	   defined, then Perl defaults to consulting first the logical name tables specified by
	   LNM$FILE_DEV, and then the CRTL "environ" array.

	   In all operations on %ENV, the key string is treated as if it were entirely uppercase,
	   regardless of the case actually specified in the Perl expression.

	   When an element of %ENV is read, the locations to which PERL_ENV_TABLES points are
	   checked in order, and the value obtained from the first successful lookup is returned.
	   If the name of the %ENV element contains a semi-colon, it and any characters after it
	   are removed.  These are ignored when the CRTL "environ" array or a CLI symbol table is
	   consulted.  However, the name is looked up in a logical name table, the suffix after
	   the semi-colon is treated as the translation index to be used for the lookup.   This
	   lets you look up successive values for search list logical names.  For instance, if
	   you say

	      $  Define STORY  once,upon,a,time,there,was
	      $  perl -e "for ($i = 0; $i <= 6; $i++) " -
	      _$ -e "{ print $ENV{'story;'.$i},' '}"

	   Perl will print "ONCE UPON A TIME THERE WAS", assuming, of course, that
	   PERL_ENV_TABLES is set up so that the logical name "story" is found, rather than a CLI
	   symbol or CRTL "environ" element with the same name.

	   When an element of %ENV is set to a defined string, the corresponding definition is
	   made in the location to which the first translation of PERL_ENV_TABLES points.  If
	   this causes a logical name to be created, it is defined in supervisor mode.	(The same
	   is done if an existing logical name was defined in executive or kernel mode; an exist-
	   ing user or supervisor mode logical name is reset to the new value.)  If the value is
	   an empty string, the logical name's translation is defined as a single NUL (ASCII 00)
	   character, since a logical name cannot translate to a zero-length string.  (This
	   restriction does not apply to CLI symbols or CRTL "environ" values; they are set to
	   the empty string.)  An element of the CRTL "environ" array can be set only if your
	   copy of Perl knows about the CRTL's "setenv()" function.  (This is present only in
	   some versions of the DECCRTL; check $Config{d_setenv} to see whether your copy of Perl
	   was built with a CRTL that has this function.)

	   When an element of %ENV is set to "undef", the element is looked up as if it were
	   being read, and if it is found, it is deleted.  (An item "deleted" from the CRTL "env-
	   iron" array is set to the empty string; this can only be done if your copy of Perl
	   knows about the CRTL "setenv()" function.)  Using "delete" to remove an element from
	   %ENV has a similar effect, but after the element is deleted, another attempt is made
	   to look up the element, so an inner-mode logical name or a name in another location
	   will replace the logical name just deleted.	In either case, only the first value
	   found searching PERL_ENV_TABLES is altered.	It is not possible at present to define a
	   search list logical name via %ENV.

	   The element $ENV{DEFAULT} is special: when read, it returns Perl's current default
	   device and directory, and when set, it resets them, regardless of the definition of
	   PERL_ENV_TABLES.  It cannot be cleared or deleted; attempts to do so are silently
	   ignored.

	   Note that if you want to pass on any elements of the C-local environ array to a sub-
	   process which isn't started by fork/exec, or isn't running a C program, you can "pro-
	   mote" them to logical names in the current process, which will then be inherited by
	   all subprocesses, by saying

	       foreach my $key (qw[C-local keys you want promoted]) {
		   my $temp = $ENV{$key}; # read from C-local array
		   $ENV{$key} = $temp;	  # and define as logical name
	       }

	   (You can't just say $ENV{$key} = $ENV{$key}, since the Perl optimizer is smart enough
	   to elide the expression.)

	   Don't try to clear %ENV by saying "%ENV = ();", it will throw a fatal error.  This is
	   equivalent to doing the following from DCL:

	       DELETE/LOGICAL *

	   You can imagine how bad things would be if, for example, the SYS$MANAGER or SYS$SYSTEM
	   logicals were deleted.

	   At present, the first time you iterate over %ENV using "keys", or "values",	you will
	   incur a time penalty as all logical names are read, in order to fully populate %ENV.
	   Subsequent iterations will not reread logical names, so they won't be as slow, but
	   they also won't reflect any changes to logical name tables caused by other programs.

	   You do need to be careful with the logicals representing process-permanent files, such
	   as "SYS$INPUT" and "SYS$OUTPUT".  The translations for these logicals are prepended
	   with a two-byte binary value (0x1B 0x00) that needs to be stripped off if you want to
	   use it. (In previous versions of Perl it wasn't possible to get the values of these
	   logicals, as the null byte acted as an end-of-string marker)

       $!  The string value of $! is that returned by the CRTL's strerror() function, so it will
	   include the VMS message for VMS-specific errors.  The numeric value of $! is the value
	   of "errno", except if errno is EVMSERR, in which case $! contains the value of
	   vaxc$errno.	Setting $!  always sets errno to the value specified.  If this value is
	   EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so that the string value of $!
	   won't reflect the VMS error message from before $! was set.

       $^E This variable provides direct access to VMS status values in vaxc$errno, which are
	   often more specific than the generic Unix-style error messages in $!.  Its numeric
	   value is the value of vaxc$errno, and its string value is the corresponding VMS mes-
	   sage string, as retrieved by sys$getmsg().  Setting $^E sets vaxc$errno to the value
	   specified.

       $?  The "status value" returned in $? is synthesized from the actual exit status of the
	   subprocess in a way that approximates POSIX wait(5) semantics, in order to allow Perl
	   programs to portably test for successful completion of subprocesses.  The low order 8
	   bits of $? are always 0 under VMS, since the termination status of a process may or
	   may not have been generated by an exception.  The next 8 bits are derived from the
	   severity portion of the subprocess' exit status: if the severity was success or infor-
	   mational, these bits are all 0; if the severity was warning, they contain a value of
	   1; if the severity was error or fatal error, they contain the actual severity bits,
	   which turns out to be a value of 2 for error and 4 for fatal error.

	   As a result, $? will always be zero if the subprocess' exit status indicated success-
	   ful completion, and non-zero if a warning or error occurred.  Conversely, when setting
	   $? in an END block, an attempt is made to convert the POSIX value into a native status
	   intelligible to the operating system upon exiting Perl.  What this boils down to is
	   that setting $?  to zero results in the generic success value SS$_NORMAL, and setting
	   $? to a non-zero value results in the generic failure status SS$_ABORT.  See also
	   "exit" in perlport.

	   The pragma "use vmsish 'status'" makes $? reflect the actual VMS exit status instead
	   of the default emulation of POSIX status described above.  This pragma also disables
	   the conversion of non-zero values to SS$_ABORT when setting $? in an END block (but
	   zero will still be converted to SS$_NORMAL).

       $|  Setting $| for an I/O stream causes data to be flushed all the way to disk on each
	   write (i.e. not just to the underlying RMS buffers for a file).  In other words, it's
	   equivalent to calling fflush() and fsync() from C.

Standard modules with VMS-specific differences
       SDBM_File

       SDBM_File works properly on VMS. It has, however, one minor difference. The database
       directory file created has a .sdbm_dir extension rather than a .dir extension. .dir files
       are VMS filesystem directory files, and using them for other purposes could cause unac-
       ceptable problems.

Revision date
       This document was last updated on 01-May-2002, for Perl 5, patchlevel 8.

AUTHOR
       Charles Bailey  bailey@cor.newman.upenn.edu Craig Berry	craigberry@mac.com Dan Sugalski
       dan@sidhe.org

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


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