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 installed.

   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-up.

   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

   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 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] 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 extensions.)

   *   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 format.

   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
   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 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 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 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.

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 together.

   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 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, 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

       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

       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

   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

       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 review.

       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

       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 ignored.

       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

       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

       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

       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

       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

       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

   $|  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


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