Provided by: perl-doc_5.28.1-6build1_all bug


       perlvms - VMS-specific documentation for Perl


       Gathered below are notes describing details of Perl 5's behavior on VMS.  They are a
       supplement 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


       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 build process, three Perl images are produced.  Miniperl.Exe is an executable
       image which contains all of the basic functionality of Perl, but cannot take advantage of
       Perl XS extensions and has a hard-wired list of library locations for loading pure-Perl
       modules.  It is used extensively to build and test Perl and various extensions, but is not

       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. It is
       generally located via the logical name PERLSHR.  While it's possible to put the image in
       SYS$SHARE to make it loadable, that's not recommended. And while you may wish to INSTALL
       the image for performance reasons, you should not install it with privileges; if you do,
       the result will not be what you expect as image privileges are disabled during Perl start-

       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,, 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

   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]
       subdirectory 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

       VMS support for this process in the current release of Perl is sufficient to handle most
       extensions.  (See the MakeMaker documentation for more details on installation options for

       ·   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

       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.

       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.

       Also when working on Perl programs on VMS, if you need a syntax in a specific operating
       system format, then you need either to check the appropriate DECC$ feature logical, or
       call a conversion routine to force it to that format.

       The feature logical name DECC$FILENAME_UNIX_REPORT modifies traditional Perl behavior in
       the conversion of file specifications from Unix to VMS format in order to follow the
       extended character handling rules now expected by the CRTL.  Specifically, when this
       feature is in effect, the "./.../" in a Unix path is now translated to "[.^.^.^.]" instead
       of the traditional VMS "[...]".  To be compatible with what MakeMaker expects, if a VMS
       path cannot be translated to a Unix path, it is passed through unchanged, so
       "unixify("[...]")" will return "[...]".

       There are several ambiguous cases where a conversion routine cannot determine whether an
       input filename is in Unix format or in VMS format, since now both VMS and Unix file
       specifications may have characters in them that could be mistaken for syntax delimiters of
       the other type. So some pathnames simply cannot be used in a mode that allows either type
       of pathname to be present.  Perl will tend to assume that an ambiguous filename is in Unix

       Allowing "." as a version delimiter is simply incompatible with determining whether a
       pathname is in VMS format or in Unix format with extended file syntax.  There is no way to
       know whether "perl-5.8.6" is a Unix "perl-5.8.6" or a VMS "perl-5.8;6" when passing it to
       unixify() or vmsify().

       The DECC$FILENAME_UNIX_REPORT logical name controls how Perl interprets filenames to the
       extent that Perl uses the CRTL internally for many purposes, and attempts to follow CRTL
       conventions for reporting filenames.  The DECC$FILENAME_UNIX_ONLY feature differs in that
       it expects all filenames passed to the C run-time to be already in Unix format.  This
       feature is not yet supported in Perl since Perl uses traditional OpenVMS file
       specifications internally and in the test harness, and it is not yet clear whether this
       mode will be useful or useable.  The feature logical name DECC$POSIX_COMPLIANT_PATHNAMES
       is new with the RMS Symbolic Link SDK and included with OpenVMS v8.3, but is not yet
       supported in Perl.

   Filename Case
       Perl enables DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE by default.  Note that the
       latter only takes effect when extended parse is set in the process in which Perl is
       running.  When these features are explicitly disabled in the environment or the CRTL does
       not support them, Perl follows the traditional CRTL behavior of downcasing command-line
       arguments and returning file specifications in lower case only.

       N. B.  It is very easy to get tripped up using a mixture of other programs, external
       utilities, and Perl scripts that are in varying states of being able to handle case
       preservation.  For example, a file created by an older version of an archive utility or a
       build utility such as MMK or MMS may generate a filename in all upper case even on an
       ODS-5 volume.  If this filename is later retrieved by a Perl script or module in a case
       preserving environment, that upper case name may not match the mixed-case or lower-case
       expectations of the Perl code.  Your best bet is to follow an all-or-nothing approach to
       case preservation: either don't use it at all, or make sure your entire toolchain and
       application environment support and use it.

       OpenVMS Alpha v7.3-1 and later and all version of OpenVMS I64 support case sensitivity as
       a process setting (see "SET PROCESS /CASE_LOOKUP=SENSITIVE"). Perl does not currently
       support case sensitivity on VMS, but it may in the future, so Perl programs should use the
       "File::Spec->case_tolerant" method to determine the state, and not the $^O variable.

   Symbolic Links
       When built on an ODS-5 volume with symbolic links enabled, Perl by default supports
       symbolic links when the requisite support is available in the filesystem and CRTL
       (generally 64-bit OpenVMS v8.3 and later).  There are a number of limitations and caveats
       to be aware of when working with symbolic links on VMS.  Most notably, the target of a
       valid symbolic link must be expressed as a Unix-style path and it must exist on a volume
       visible from your POSIX root (see the "SHOW ROOT" command in DCL help).  For further
       details on symbolic link capabilities and requirements, see chapter 12 of the CRTL manual
       that ships with OpenVMS v8.3 or later.

   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
       filespecs will follow VMS syntax; if a Unix-style filespec is passed in, Unix-style
       filespecs will be returned.  Similar to the behavior of wildcard globbing for a Unix
       shell, one can escape command line wildcards with double quotation marks """ around a perl
       program command line argument.  However, owing to the stripping of """ characters carried
       out by the C handling of argv you will need to escape a construct such as this one (in a
       directory containing the files PERL.C, PERL.EXE, PERL.H, and PERL.OBJ):

           $ perl -e "print join(' ',@ARGV)" perl.*
           perl.c perl.exe perl.h perl.obj

       in the following triple quoted manner:

           $ perl -e "print join(' ',@ARGV)" """perl.*"""

       In both the case of unquoted command line arguments or in calls to "glob()" 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
       performed by Unix shells.)

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

       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

       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
       subprocess to complete before continuing.

       The mailbox (MBX) that perl can create to communicate with a pipe defaults to a buffer
       size of 8192 on 64-bit systems, 512 on VAX.  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 set the mailbox size to 32767 use
       "$ENV{'PERL_MBX_SIZE'} = 32767;" and then open and use pipe constructs.  An alternative
       would be to issue the command:

           $ Define PERL_MBX_SIZE 32767

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


       The PERL5LIB and PERLLIB environment elements work as documented in perl, except that the
       element separator is, by default, '|' instead of ':'.  However, when running under a Unix
       shell as determined by the logical name "GNV$UNIX_SHELL", the separator will be ':' as on
       Unix systems. The directory specifications may use either VMS or Unix syntax.

The Perl Forked Debugger

       The Perl forked debugger places the debugger commands and output in a separate X-11
       terminal window so that commands and output from multiple processes are not mixed

       Perl on VMS supports an emulation of the forked debugger when Perl is run on a VMS system
       that has X11 support installed.

       To use the forked debugger, you need to have the default display set to an X-11 Server and
       some environment variables set that Unix expects.

       The forked debugger requires the environment variable "TERM" to be "xterm", and the
       environment variable "DISPLAY" to exist.  "xterm" must be in lower case.

         $define TERM "xterm"

         $define DISPLAY "hostname:0.0"

       Currently the value of "DISPLAY" is ignored.  It is recommended that it be set to be the
       hostname of the display, the server and screen in Unix notation.  In the future the value
       of DISPLAY may be honored by Perl instead of using the default display.

       It may be helpful to always use the forked debugger so that script I/O is separated from
       debugger I/O.  You can force the debugger to be forked by assigning a value to the logical
       name <PERLDB_PIDS> that is not a process identification number.

         $define PERLDB_PIDS XXXX


       The PERL_VMS_EXCEPTION_DEBUG being defined as "ENABLE" will cause the VMS debugger to be
       invoked if a fatal exception that is not otherwise handled is raised.  The purpose of this
       is to allow debugging of internal Perl problems that would cause such a condition.

       This allows the programmer to look at the execution stack and variables to find out the
       cause of the exception.  As the debugger is being invoked as the Perl interpreter is about
       to do a fatal exit, continuing the execution in debug mode is usually not practical.

       Starting Perl in the VMS debugger may change the program execution profile in a way that
       such problems are not reproduced.

       The "kill" function can be used to test this functionality from within a program.

       In typical VMS style, only the first letter of the value of this logical name is actually
       checked in a case insensitive mode, and it is considered enabled if it is the value
       "T","1" or "E".

       This logical name must be defined before Perl is started.

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:

       ·   "<file" reads stdin from "file",

       ·   ">file" writes stdout to "file",

       ·   ">>file" appends stdout to "file",

       ·   "2>file" writes stderr to "file",

       ·   "2>>file" appends stderr to "file", and

       ·   "2>&1" redirects stderr to stdout.

       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
       perlrun.  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.

       On newer 64 bit versions of OpenVMS, a process setting now controls if the quoting is
       needed to preserve the case of command line arguments.

       -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
           version under the original filename.)

       -S  If the "-S" or "-"S"" switch is present and the script name does not contain a
           directory, 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
           specified, 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
           compiled, 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
       implemented in the VMS port of Perl (functions marked with * are discussed in more detail

           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, endgrent, endpwent, eof, eval, exec*, exists, exit, exp,
           fileno, flock  getc, getgrent*, getgrgid*, getgrnam, getlogin,
           getppid, getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
           grep, hex, ioctl, import, index, int, join, keys, kill*,
           last, lc, lcfirst, lchown*, length, link*, local, localtime, log,
           lstat, 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, readlink*, redo, ref,
           rename, require, reset, return, reverse, rewinddir, rindex,
           rmdir, s///, scalar, seek, seekdir, select(internal),
           select (system call)*, setgrent, setpwent, shift, sin, sleep,
           socketpair, sort, splice, split, sprintf, sqrt, srand, stat,
           study, substr, symlink*, 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, fork*, getpgrp, getpriority,
           msgctl, msgget, msgsend, msgrcv, semctl,
           semget, semop, setpgrp, setpriority, shmctl, shmget,
           shmread, shmwrite, syscall

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


       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

       The following function is available on Perls built on 64 bit OpenVMS v8.2 with hard links
       enabled on an ODS-5 formatted build disk.  CRTL support is in principle available as of
       OpenVMS v7.3-1, and better configuration support could detect this.


       The following functions are available on Perls built on 64 bit OpenVMS v8.2 and later.
       CRTL support is in principle available as of OpenVMS v7.3-2, and better configuration
       support could detect this.

          getgrgid, getgrnam, getpwnam, getpwuid,
          setgrent, ttyname

       The following functions are available on Perls built on 64 bit OpenVMS v8.2 and later.

          statvfs, socketpair

       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
           meaningful 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.

           There are DECC feature logical names AND ODS-5 volume attributes that also control
           what values are returned for the date fields.

           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 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
           different 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
           necessary.  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) = @_;
                   if ( !($pwdhash = (getpwnam($user))[1]) ||
                          $pwdhash ne crypt("\U$passwd","\U$name") ) {
                   return 1;

       die "die" will force the native VMS exit status to be an SS$_ABORT code if neither of the
           $! or $? status values are ones that would cause the native status to be interpreted
           as being what VMS classifies as SEVERE_ERROR severity for DCL error handling.

           When "PERL_VMS_POSIX_EXIT" is active (see "$?" below), the native VMS exit status
           value will have either one of the $! or $? or $^E or the Unix value 255 encoded into
           it in a way that the effective original value can be decoded by other programs written
           in C, including Perl and the GNV package.  As per the normal non-VMS behavior of "die"
           if either $! or $? are non-zero, one of those values will be encoded into a native VMS
           status value.  If both of the Unix status values are 0, and the $^E value is set one
           of ERROR or SEVERE_ERROR severity, then the $^E value will be used as the exit code as
           is.  If none of the above apply, the Unix value of 255 will be encoded into a native
           VMS exit status value.

           Please note a significant difference in the behavior of "die" in the
           "PERL_VMS_POSIX_EXIT" mode is that it does not force a VMS SEVERE_ERROR status on
           exit.  The Unix exit values of 2 through 255 will be encoded in VMS status values with
           severity levels of SUCCESS.  The Unix exit value of 1 will be encoded in a VMS status
           value with a severity level of ERROR.  This is to be compatible with how the VMS C
           library encodes these values.

           The minimum severity level set by "die" in "PERL_VMS_POSIX_EXIT" mode may be changed
           to be ERROR or higher in the future depending on the results of testing and further

           See "$?" for a description of the encoding of the Unix value to produce a native VMS
           status containing it.

           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
           argument 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
           filespec) 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.

           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
           support 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.

           These operators obtain the information described in perlfunc, if you have the
           privileges 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
           directory in Unix syntax. The $gcos item contains the owner field from the UAF record.
           The $quota item is not used.

           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
           neither of these cases is true, a warning message is printed, and "undef" is returned.

           In most cases, "kill" is implemented via the undocumented system service $SIGPRC,
           which has the same calling sequence as $FORCEX, but throws an exception in the target
           process rather than forcing it to call $EXIT.  Generally speaking, "kill" follows the
           behavior of the CRTL's "kill()" function, but unlike that function can be called from
           within a signal handler.  Also, unlike the "kill" in some versions of the CRTL, Perl's
           "kill" checks the validity of the signal passed in and returns an error rather than
           attempting to send an unrecognized signal.

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

           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.

           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.

           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
           especially 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
           versions, 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
           $Config{'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
           protection (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::Filespec::candelete" operator.  For instance, in order to delete only files to
           which you have delete access, you could say something like

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

           (or you could just use "VMS::Stdio::remove", if you've installed the VMS::Stdio
           extension 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.

           This behavior of "unlink" is to be compatible with POSIX behavior and not traditional
           VMS behavior.

       utime LIST
           This operator changes only the modification time of the file (VMS revision date) on
           ODS-2 volumes and ODS-5 volumes without access dates enabled. On ODS-5 volumes with
           access dates enabled, the true access time is modified.

       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
           created 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
       information takes precedence.

           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
           specifies 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:

               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 some
               embedded Perl applications or when running under a shell such as GNV bash, the
               "environ" array may have been populated by the calling program.

               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
               characters 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$FILE_DEV, and then the CRTL "environ" array.  This default order is reversed when
           the logical name GNV$UNIX_SHELL is defined, such as when running under GNV bash.

           For operations on %ENV entries based on logical names or DCL symbols, the key string
           is treated as if it were entirely uppercase, regardless of the case actually specified
           in the Perl expression. Entries in %ENV based on the CRTL's environ array preserve the
           case of the key string when stored, and lookups are case sensitive.

           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
           existing 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 "\0") 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.)

           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
           "environ" array is set to the empty string.)  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

           Note that if you want to pass on any elements of the C-local environ array to a
           subprocess which isn't started by fork/exec, or isn't running a C program, you can
           "promote" 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
           logical names 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 logical names representing process-permanent files,
           such as "SYS$INPUT" and "SYS$OUTPUT".  The translations for these logical names 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 logical names, 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
           message string, as retrieved by sys$getmsg().  Setting $^E sets vaxc$errno to the
           value specified.

           While Perl attempts to keep the vaxc$errno value to be current, if errno is not
           EVMSERR, it may not be from the current operation.

       $?  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 contain the termination status of the program.

           If the child process follows the convention of C programs compiled with the
           _POSIX_EXIT macro set, the status value will contain the actual value of 0 to 255
           returned by that program on a normal exit.

           With the _POSIX_EXIT macro set, the Unix exit value of zero is represented as a VMS
           native status of 1, and the Unix values from 2 to 255 are encoded by the equation:

              VMS_status = 0x35a000 + (unix_value * 8) + 1.

           And in the special case of Unix value 1 the encoding is:

              VMS_status = 0x35a000 + 8 + 2 + 0x10000000.

           For other termination statuses, the severity portion of the subprocess's exit status
           is used: if the severity was success or informational, 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 severe_error.  Fatal is another term for the severe_error status.

           As a result, $? will always be zero if the subprocess's exit status indicated
           successful completion, and non-zero if a warning or error occurred or a program
           compliant with encoding _POSIX_EXIT values was run and set a status.

           How can you tell the difference between a non-zero status that is the result of a VMS
           native error status or an encoded Unix status?  You can not unless you look at the
           ${^CHILD_ERROR_NATIVE} value.  The ${^CHILD_ERROR_NATIVE} value returns the actual VMS
           status value and check the severity bits. If the severity bits are equal to 1, then if
           the numeric value for $? is between 2 and 255 or 0, then $? accurately reflects a
           value passed back from a Unix application.  If $? is 1, and the severity bits indicate
           a VMS error (2), then $? is from a Unix application exit value.

           In practice, Perl scripts that call programs that return _POSIX_EXIT type status
           values will be expecting those values, and programs that call traditional VMS programs
           will either be expecting the previous behavior or just checking for a non-zero status.

           And success is always the value 0 in all behaviors.

           When the actual VMS termination status of the child is an error, internally the $!
           value will be set to the closest Unix errno value to that error so that Perl scripts
           that test for error messages will see the expected Unix style error message instead of
           a VMS message.

           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.

           With the "PERL_VMS_POSIX_EXIT" logical name defined as "ENABLE", setting $? will cause
           the new value to be encoded into $^E so that either the original parent or child exit
           status values
            0 to 255 can be automatically recovered by C programs expecting _POSIX_EXIT behavior.
           If both a parent and a child exit value are non-zero, then it will be assumed that
           this is actually a VMS native status value to be passed through.  The special value of
           0xFFFF is almost a NOOP as it will cause the current native VMS status in the C
           library to become the current native Perl VMS status, and is handled this way as it is
           known to not be a valid native VMS status value.  It is recommend that only values in
           the range of normal Unix parent or child status numbers, 0 to 255 are used.

           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).

           Do not use the pragma "use vmsish 'status'" with "PERL_VMS_POSIX_EXIT" enabled, as
           they are at times requesting conflicting actions and the consequence of ignoring this
           advice will be undefined to allow future improvements in the POSIX exit handling.

           In general, with "PERL_VMS_POSIX_EXIT" enabled, more detailed information will be
           available in the exit status for DCL scripts or other native VMS tools, and will give
           the expected information for Posix programs.  It has not been made the default in
           order to preserve backward compatibility.

           N.B. Setting "DECC$FILENAME_UNIX_REPORT" implicitly enables "PERL_VMS_POSIX_EXIT".

       $|  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 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
       unacceptable problems.

Revision date

       Please see the git repository for revision history.


       Charles Bailey Craig Berry Dan Sugalski John Malmberg