PERLVMS(1)

📦
version 5.42.3 · 22 versions
, in fedora 43, fedora 44

✨ NAME ✨

perlvms — VMS-specific documentation for Perl. This is the PERLVMS(1) page from the Perl Programmers Reference Guide, bestie. iykyk.

💖 DESCRIPTION 💖

okay so bestie, 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 vmsperl@perl.org.

🎀 Installation 🎀

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

🦋 Organization of Perl Images 🦋

okay so the image situation is a whole vibe. Let's break it down.

🧚 Core Images 🧚

During the build process, three Perl images are produced.

  • Miniperl.Exe — 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.
  • PerlShr.Exe — the shareable image where most of the complete Perl resides. It 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.
  • Perl.Exe — finally, 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.

  • Static configuration — the object code for the extension is linked directly into PerlShr.Exe, and is initialized whenever Perl is invoked.
  • 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 used or required in your script. This allows you to maintain the extension as a separate entity, at the cost of keeping track of the additional shareable image.

Most extensions can be set up as either static or dynamic.

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

💅 Installing static extensions 💅

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

Finally, you'll need to copy the extension's Perl library module to the [.Extname] 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 🎀

✨ Syntax ✨

okay so bestie, the whole goal here is that Perl lowkey knows about both VMS-style and Unix-style file specifications wherever it possibly can. You can use either style, or both, on the command line and in scripts — but the one thing you absolutely cannot do is combine the two styles inside a single file specification. Pick a lane for each filespec, periodt.

VMS Perl reads Unix pathnames pretty much the same way the CRTL does — like, the first component of an absolute path gets read as the device name for the VMS file specification. And there's a whole set of functions chilling in the VMS::Filespec package for explicit interconversion between VMS and Unix syntax, so if you need the details, go read its documentation 💖

They've tried to minimize how much Perl library modules depend on Unix syntax, but ngl you may still find that some of them — plus some scripts written for Unix systems — will require you to use Unix syntax, because they just assume that / is the directory separator, etc. If you find instances of this in the Perl distribution itself, please let us know, so they can try to work around them 🙏

Also, when you're 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. no shortcuts, bestie.

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

There are several ambiguous cases where a conversion routine literally cannot tell whether an input filename is in Unix format or in VMS format, since now both VMS and Unix file specifications may contain characters 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. When it's ambiguous, Perl will tend to assume the 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(). it's giving genuinely undecidable, and not in a fun way 😭

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. That 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 either. 🫶

🌸 Filename Case 🌸

Perl enables DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE by default. Heads up though: 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 just doesn't 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. no in-between, bestie 💅

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. write that down 📝

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. go read chapter 12, i'm serious 👑

🌈 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. matchy matchy, love that for us ✨

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.*"""
    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.) see, it's all about matching the vibe of the Unix shell 🐚

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

💜 Pipes 💜

Input and output pipes to Perl filehandles are supported; the "file name" is passed to lib$spawn() for asynchronous execution. You should be careful to close any pipes you have opened in a Perl script, lest you leave any "orphaned" subprocesses around when Perl exits. orphaned processes are NOT the vibe, bestie 😭

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. so patient of her 💖

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. tradeoffs, always tradeoffs 🎀

🧚 PERL5LIB and PERLLIB 🧚

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. flexible queen behavior 👑

🌟 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. separate windows = separate vibes, no chaos, love that 🌸

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. lowercase only, do not test her on this 💅

  $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. manifesting that for a future release ✨

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

💥 PERL_VMS_EXCEPTION_DEBUG 💥

Okay so if you define the logical name PERL_VMS_EXCEPTION_DEBUG as "ENABLE", then whenever a fatal exception gets raised that isn't handled by anything else, the VMS debugger gets invoked. Why would you want that? So you can actually debug internal Perl problems that would cause a condition like that. 👑

This lets the programmer look at the execution stack and the variables to find out what caused the exception. But real talk — since the debugger is being invoked right as the Perl interpreter is about to do a fatal exit, continuing the execution in debug mode is usually not practical. 😭

Also, starting Perl in the VMS debugger may change the program execution profile in a way that such problems are not reproduced. Classic. 💀

You can use the kill function to test this functionality from within a program.

And 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's considered enabled if it's the value "T", "1" or "E".

This logical name must be defined before Perl is started. fr fr, order matters.

🎀 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.

On top of that, 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, and that subprocess takes the output of Perl as its input. 🫶

And finally — if the command line ends with '&', the entire command is run in the background as an asynchronous subprocess. main character energy, off doing its own thing. ✨

🎛️ Command line switches

The following command line switches behave differently under VMS than described in perlrun. Also note 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:

truncate

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

fcntl (without locking)

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

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

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.

link

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. And 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. iykyk.

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

💫 backticks

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

🫧 binmode FILEHANDLE

The binmode operator will attempt to ensure 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. 😭 heads up!

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 ensure that you'll get the proper value:

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

💀 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 (peep $? down below bestie), the native VMS exit status value gets either one of $!, $?, $^E, or the Unix value 255 encoded into it, in a way that other C programs — including Perl and the GNV package — can decode back to the effective original value. ✨

So like, per the normal non-VMS behavior of die: if either $! or $? is non-zero, one of those values gets encoded into a native VMS status value. If both Unix status values are 0 and the $^E value is set with either ERROR or SEVERE_ERROR severity, then $^E is used as the exit code, as is. And if none of the above apply? The Unix value 255 gets encoded into a native VMS exit status value. 💅

Okay bestie, this next bit is a significant difference, no cap: in PERL_VMS_POSIX_EXIT mode, die does not force a VMS SEVERE_ERROR status on exit. Unix exit values 2 through 255 get encoded into VMS status values with severity levels of SUCCESS. The Unix exit value 1 gets encoded into 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.

🌸 dump

Rather than causing Perl to abort and dump core, the dump operator invokes the VMS debugger. 🐛 If you keep executing the Perl program under the debugger, control gets transferred to the label specified as the argument to dump, or — if no label was specified — back to the beginning of the program. All the other state of the program (like values of variables, open file handles) is not affected by calling dump. Obsessed, honestly.

🌈 exec LIST

A call to exec makes Perl exit, and invokes 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's 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. 🦋

💀 fork

Okay so in principle the fork operator could be implemented via the CRTL vfork() routine (with the same rather severe limitations), and some internal support to do exactly that is in place — but 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, bestie.

🎀 getpwent, getpwnam, getpwuid

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.

  • $dir contains the login directory in VMS syntax
  • $comment contains the login directory in Unix syntax
  • $gcos contains the owner field from the UAF record
  • $quota is not used

⏰ gmtime

The gmtime operator functions 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're 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. 🙈

🔥 kill

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 it 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.

🧚 qx//

See the entry on backticks above. 💖

⭐ select (system call)

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

🍓 stat EXPR

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

We can't guarantee this, though, so caveat scriptor. 😭

🌟 system LIST

The system operator creates a subprocess, and passes its arguments to the subprocess for execution as a DCL command. Since the subprocess is created directly via lib$spawn(), any valid DCL command string may be specified.

If the string begins with '@', it's 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 lets you invoke an image directly just by passing the file specification to system — a common Unixish idiom. 🦋 If the token has no file type, and matches a file with null type, then an attempt is made to determine whether the file is an executable image which should be invoked using MCR or a text file which should be passed to DCL as a command procedure.

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

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

🕰️ time

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

⏳ times

The array returned by the times operator is divided up according to the same rules as the CRTL times() routine. So like:

  • the "system time" elements will always be 0, since there's no difference between "user time" and "system" time under VMS
  • 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 deletes 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 deletes 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 {
    my($file,$num);
    foreach $file (@_) {
        next unless VMS::Filespec::candelete($file);
        $num += unlink $file;
    }
    $num;
}

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

🌸 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 waits for that subprocess, and returns its final status value in $?. If PID is a subprocess created in some other way (e.g. SPAWNed before Perl was invoked), waitpid simply checks once per second whether the process has completed, and returns 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. Like, fully ignored, don't even bother. 💅

✨ Perl variables ✨

okay bestie this is the part where VMS gets extra with the "special" Perl variables. The info below applies to the ones listed, on top of everything the general docs in perlvar already told you. And if the two ever beef? this one wins. No cap.

🫶 %ENV

The way %ENV behaves depends entirely on how the logical name PERL_ENV_TABLES translates. If it's defined, it should be a search list, and each element of that list is a place where %ENV elements can live. So when you tell Perl "hey read this" or "hey set this" for $ENV{"name"}, Perl goes down the translations of PERL_ENV_TABLES like a checklist:

💖 CRTL_ENV

This string tells Perl to go poke the CRTL's internal environ array of key-value pairs, using name as the key. Most of the time that array is basically tiny — only a few keys — but if Perl got invoked through the C exec[lv]e() function, like in some embedded Perl applications or when you're running under a shell such as GNV bash, then the environ array may have been populated by whatever program called it. plot twist ✨

💖 CLISYM_[LOCAL]

A string that starts with CLISYM_ tells Perl to consult the CLI's symbol tables, using name as the name of the symbol. When you're reading an element of %ENV, the local symbol table gets scanned first, and then the global symbol table.

The characters that come after CLISYM_ actually matter when you set or delete an element of %ENV: if the whole string is exactly CLISYM_LOCAL, the change happens in the local symbol table. Any other ending? Then the global symbol table is the one that gets changed. 🎀

💖 Any other string

If an element of PERL_ENV_TABLES translates to literally anything else, that string is used as the name of a logical name table, and Perl consults it using name as the logical name. The normal search order of access modes applies, as usual. 🦋

PERL_ENV_TABLES gets translated once, right when Perl starts up. So any changes you make while Perl is running? They do not affect how %ENV behaves. Sorry bestie, that's just how it is. 😭

If PERL_ENV_TABLES isn't defined at all, then Perl defaults to consulting first the logical name tables specified by LNM$FILE_DEV, and then the CRTL environ array. And this default order gets reversed when the logical name GNV$UNIX_SHELL is defined — like when you're running under GNV bash. Sneaky, right?

For operations on %ENV entries that are based on logical names or DCL symbols, the key string gets treated as if it were entirely uppercase, no matter what case you actually typed in the Perl expression. Meanwhile, entries in %ENV based on the CRTL's environ array preserve the case of the key string when stored, and lookups there are case sensitive. So like... two different personalities in one hash. 💀

When you read an element of %ENV, the locations PERL_ENV_TABLES points to get checked in order, and the value from the first successful lookup is what you get back. Here's a fun one: if the name of the %ENV element contains a semi-colon, that semi-colon and anything after it get removed. Those bits are ignored when the CRTL environ array or a CLI symbol table is being consulted. But if the name gets looked up in a logical name table, the suffix after the semi-colon is treated as the translation index to use for the lookup. Which means you can look up successive values of search list logical names. Iconic behavior honestly. 🎀

So 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, obviously, that PERL_ENV_TABLES is set up so the logical name "story" is the thing that's found, and not a CLI symbol or a CRTL environ element with the same name. 🌸

When you set an element of %ENV to a defined string, the corresponding definition gets made in the location that the first translation of PERL_ENV_TABLES points to. If that causes a logical name to be created, it's defined in supervisor mode. (And the same thing happens if an existing logical name was defined in executive or kernel mode; an existing user or supervisor mode logical name just gets reset to the new value.) If the value is an empty string, the logical name's translation gets defined as a single NUL (ASCII "\0") character — because a logical name literally cannot translate to a zero-length string, bestie, it's just not allowed. (That restriction doesn't apply to CLI symbols or CRTL environ values though; those just get set to the empty string.) 🫶

When you set an element of %ENV to undef, the element gets looked up as if it were being read, and if it's found, it gets deleted. (An item that gets "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 the element up again. So an inner-mode logical name, or a name sitting in another location, will replace the logical name you just deleted. In either case, only the first value found while searching PERL_ENV_TABLES gets altered. And heads up: it is not possible at present to define a search list logical name via %ENV. 😭

The element $ENV{DEFAULT} is special: when you read it, it returns Perl's current default device and directory, and when you set it, it resets them — regardless of how PERL_ENV_TABLES is defined. You can't clear it or delete it; any attempt to do so is silently ignored. It said what it said. 👑

Note that if you want to pass on any elements of the C-local environ array to a subprocess that isn't started by fork/exec, or that 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. Rude, but fair.)

🚨 Do not try to clear %ENV by saying %ENV = (); — it will throw a fatal error. That's equivalent to doing the following from DCL:
DELETE/LOGICAL *

And you can just imagine how bad things would get if, say, the SYS$MANAGER or SYS$SYSTEM logical names got deleted. Actual nightmare fuel. 💀

At present, the first time you iterate over %ENV using keys, or values, you'll take a time penalty while all the logical names get read, just to fully populate %ENV. Subsequent iterations won't 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. Pick your poison. 🦋

You do need to be careful with the logical names that represent process-permanent files, like SYS$INPUT and SYS$OUTPUT. The translations for those logical names are prepended with a two-byte binary value (0x1B 0x00) that you need to strip off if you actually want to use it. (In previous versions of Perl it wasn't even possible to get the values of these logical names, because the null byte acted as an end-of-string marker. So... progress, I guess?) ✨

🎀 $!

The string value of $! is whatever the CRTL's strerror() function returns, 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 $! always sets errno to the value you specified. And if that value is EVMSERR, it also sets vaxc$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 gives you direct access to VMS status values in vaxc$errno, which are often way more specific than the generic Unix-style error messages hanging out 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 you specified. 🫶

While Perl does attempt to keep the vaxc$errno value current, if errno is not EVMSERR, it may not actually be from the current operation. So like, don't @ it. 🙈

⭐ $?

The "status value" you get back in $? is synthesized from the actual exit status of the subprocess, in a way that approximates POSIX wait(5) semantics — all so Perl programs can portably test whether subprocesses completed successfully. 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, then 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 gets 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. And "fatal" is just 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 if a program compliant with encoding _POSIX_EXIT values was run and set a status.

So how can you tell the difference between a non-zero status that's the result of a VMS native error status versus an encoded Unix status? You can not — not unless you look at the ${^CHILD_ERROR_NATIVE} value. That value returns the actual VMS status value, so you 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. iykyk. 🧚

In practice, Perl scripts that call programs returning _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. Both vibes are valid. 💜

And success is always the value 0 in all behaviors. Periodt.

When the actual VMS termination status of the child is an error, internally the $! value gets set to the closest Unix errno value to that error, so Perl scripts that test for error messages see the expected Unix style error message instead of a VMS message. It's giving translation services, fr fr.

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: 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 for the receipts.

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 recommended that only values in the range of normal Unix parent or child status numbers, 0 to 255 are used. No cap.

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). Lowkey a vibe shift.

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. Bestie, this is a hard no. 🚫

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. So it's opt-in, iykyk.

N.B. Setting DECC$FILENAME_UNIX_REPORT implicitly enables PERL_VMS_POSIX_EXIT. Plot twist!

$| — 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. It's giving main character energy for your I/O. 💅

✨ Standard modules with VMS-specific differences ✨

💾 SDBM_File 💾

SDBM_File works properly on VMS. It has, however, one minor difference. The database directory file created has a .sdbm_dir extension rather than a .dir extension. .dir files are VMS filesystem directory files, and using them for other purposes could cause unacceptable problems. So don't play with .dir files like that, bestie. 🛑

🗓️ Revision date 🗓️

Please see the git repository for revision history. 🦋 (Yes, that's literally all it says.)

👑 AUTHOR 👑

  • Charles Bailey — bailey@cor.newman.upenn.edu
  • Craig Berry — craigberry@mac.com
  • Dan Sugalski — dan@sidhe.org
  • John Malmberg — wb8tyw@qsl.net

Legends, all of them. 👑✨

This page is from perl v5.42.3, dated 2026-08-03, and it's PERLVMS(1). Stay slay, bestie. 💅🫶

📦 where this page comes from