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PERLVMS(1) Perl Programmers Reference Guide PERLVMS(1)
NAME
perlvms - VMS-specific documentation for Perl
DESCRIPTION
Gathered below are notes describing details of Perl 5's behavior on VMS. They are a 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 vmsperlATperl.org.
Installation
Directions for building and installing Perl 5 can be found in the file README.vms in the main source directory of the
Perl distribution..
Organization of Perl Images
Core Images
During the installation process, three Perl images are produced. Miniperl.Exe is an executable image which contains all
of the basic functionality of Perl, but cannot take advantage of Perl extensions. It is used to generate several files
needed to build the complete Perl and various extensions. Once you've finished installing Perl, you can delete this
image.
Most of the complete Perl resides in the shareable image PerlShr.Exe, which provides a core to which the Perl executable
image and all Perl extensions are linked. You should place this image in Sys$Share, or define the logical name PerlShr
to translate to the full file specification of this image. It should be world readable. (Remember that if a user has
execute only access to PerlShr, VMS will treat it as if it were a privileged shareable image, and will therefore require
all downstream shareable images to be INSTALLed, etc.)
Finally, Perl.Exe is an executable image containing the main entry point for Perl, as well as some initialization code.
It should be placed in a public directory, and made world executable. In order to run Perl with command line arguments,
you should define a foreign command to invoke this image.
Perl Extensions
Perl extensions are packages which provide both XS and Perl code to add new functionality to perl. (XS is a meta-
language which simplifies writing C code which interacts with Perl, see perlxs for more details.) The Perl code for an
extension is treated like any other library module - it's made available in your script through the appropriate "use" or
"require" statement, and usually defines a Perl package containing the extension.
The portion of the extension provided by the XS code may be connected to the rest of Perl in either of two ways. In the
static configuration, the object code for the extension is linked directly into PerlShr.Exe, and is initialized whenever
Perl is invoked. In the dynamic configuration, the extension's machine code is placed into a separate shareable image,
which is mapped by Perl's DynaLoader when the extension is "use"d or "require"d in your script. This allows you to
maintain the extension as a separate entity, at the cost of keeping track of the additional shareable image. Most
extensions can be set up as either static or dynamic.
The source code for an extension usually resides in its own directory. At least three files are generally provided:
Extshortname.xs (where Extshortname is the portion of the extension's name following the last "::"), containing the XS
code, Extshortname.pm, the Perl library module for the extension, and Makefile.PL, a Perl script which uses the
"MakeMaker" library modules supplied with Perl to generate a Descrip.MMS file for the extension.
Installing static extensions
Since static extensions are incorporated directly into PerlShr.Exe, you'll have to rebuild Perl to incorporate a new
extension. You should edit the main Descrip.MMS or Makefile you use to build Perl, adding the extension's name to the
"ext" macro, and the extension's object file to the "extobj" macro. You'll also need to build the extension's object
file, either by adding dependencies to the main Descrip.MMS, or using a separate Descrip.MMS for the extension. Then,
rebuild PerlShr.Exe to incorporate the new code.
Finally, you'll need to copy the extension's Perl library module to the [.Extname] 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
N.B. The procedure by which extensions are built and tested creates several levels (at least 4) under the directory in
which the extension's source files live. For this reason if you are running a version of VMS prior to V7.1 you shouldn't
nest the source directory too deeply in your directory structure lest you exceed RMS' maximum of 8 levels of subdirectory
in a filespec. (You can use rooted logical names to get another 8 levels of nesting, if you can't place the files near
the top of the physical directory structure.)
VMS support for this process in the current release of Perl is sufficient to handle most extensions. However, it does
not yet recognize extra libraries required to build shareable images which are part of an extension, so these must be
added to the linker options file for the extension by hand. For instance, if the PGPLOT extension to Perl requires the
PGPLOTSHR.EXE shareable image in order to properly link the Perl extension, then the line "PGPLOTSHR/Share" must be added
to the linker options file PGPLOT.Opt produced during the build process for the Perl extension.
By default, the shareable image for an extension is placed in the [.lib.site_perl.autoArch.Extname] directory of the
installed Perl directory tree (where Arch is VMS_VAX or VMS_AXP, and Extname is the name of the extension, with each "::"
translated to "."). (See the MakeMaker documentation for more details on installation options for extensions.) However,
it can be manually placed in any of several locations:
o 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 $], with '.' converted to '_'), or
o one of the directories in @INC, or
o a directory which the extensions Perl library module passes to the DynaLoader when asking it to map the shareable
image, or
o Sys$Share or Sys$Library.
If the shareable image isn't in any of these places, you'll need to define a logical name Extshortname, where
Extshortname is the portion of the extension's name after the last "::", which translates to the full file specification
of the shareable image.
File specifications
Syntax
We have tried to make Perl aware of both VMS-style and Unix-style file specifications wherever possible. You may use
either style, or both, on the command line and in scripts, but you may not combine the two styles within a single file
specification. VMS Perl interprets Unix pathnames in much the same way as the CRTL (e.g. the first component of an
absolute path is read as the device name for the VMS file specification). There are a set of functions provided in the
"VMS::Filespec" package for explicit interconversion between VMS and Unix syntax; its documentation provides more
details.
We've tried to minimize the dependence of Perl library modules on Unix syntax, but you may find that some of these, as
well as some scripts written for Unix systems, will require that you use Unix syntax, since they will assume that '/' is
the directory separator, etc. If you find instances of this in the Perl distribution itself, please let us know, so we
can try to work around them.
Also when working on Perl programs on VMS, if you need a syntax in a specific operating system format, then you need
either to check the appropriate DECC$ feature logical, or call a conversion routine to force it to that format.
The feature logical name DECC$FILENAME_UNIX_REPORT modifies traditional Perl behavior in the conversion of file
specifications from Unix to VMS format in order to follow the extended character handling rules now expected by the CRTL.
Specifically, when this feature is in effect, the "./.../" in a Unix path is now translated to "[.^.^.^.]" instead of the
traditional VMS "[...]". To be compatible with what MakeMaker expects, if a VMS path cannot be translated to a Unix
path, it is passed through unchanged, so "unixify("[...]")" will return "[...]".
The handling of extended characters is largely complete in the VMS-specific C infrastructure of Perl, but more work is
still needed to fully support extended syntax filenames in several core modules. In particular, at this writing
PathTools has only partial support for directories containing some extended characters.
There are several ambiguous cases where a conversion routine cannot determine whether an input filename is in Unix format
or in VMS format, since now both VMS and Unix file specifications may have characters in them that could be mistaken for
syntax delimiters of the other type. So some pathnames simply cannot be used in a mode that allows either type of
pathname to be present. Perl will tend to assume that an ambiguous filename is in Unix format.
Allowing "." as a version delimiter is simply incompatible with determining whether a pathname is in VMS format or in
Unix format with extended file syntax. There is no way to know whether "perl-5.8.6" is a Unix "perl-5.8.6" or a VMS
"perl-5.8;6" when passing it to unixify() or vmsify().
The DECC$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
Perl follows VMS defaults and override settings in preserving (or not preserving) filename case. Case is not preserved
on ODS-2 formatted volumes on any architecture. On ODS-5 volumes, filenames may be case preserved depending on process
and feature settings. Perl now honors DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE on those systems where the CRTL
supports these features. When these features are not enabled 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 expections 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 suppport 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.*"""
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.
Pipes
Input and output pipes to Perl filehandles are supported; the "file name" is passed to lib$spawn() for asynchronous
execution. You should be careful to close any pipes you have opened in a Perl script, lest you leave any "orphaned"
subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose output is used as the return value of the expression. The
string between the backticks is handled as if it were the argument to the "system" operator (see below). In this case,
Perl will wait for the subprocess to complete before continuing.
The mailbox (MBX) that perl can create to communicate with a pipe defaults to a buffer size of 8192 on 64-bit systems,
512 on VAX. The default buffer size is adjustable via the logical name PERL_MBX_SIZE provided that the value falls
between 128 and the SYSGEN parameter MAXBUF inclusive. For example, to set the mailbox size to 32767 use
"$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.
PERL5LIB and PERLLIB
The PERL5LIB and PERLLIB logical names work as documented in perl, except that the element separator is '|' instead of
':'. The directory specifications may use either VMS or Unix syntax.
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
PERL_VMS_EXCEPTION_DEBUG
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
usally 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:
o "<file" reads stdin from "file",
o ">file" writes stdout to "file",
o ">>file" appends stdout to "file",
o "2>file" writes stderr to "file",
o "2>>file" appends stderr to "file", and
o "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:
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. Since real and effective UIC don't differ under VMS, "-O", "-R", "-W", and "-X" are
equivalent to "-o", "-r", "-w", and "-x". Similarly, several other tests, including "-A", "-g", "-k", "-l", "-p",
and "-u", aren't particularly meaningful under VMS, and the values returned by these tests reflect whatever your CRTL
"stat()" routine does to the equivalent bits in the st_mode field. Finally, "-d" returns true if passed a device
specification without an explicit directory (e.g. "DUA1:"), as well as if passed a directory.
There are DECC feature logical names AND ODS-5 volume attributes that also control what values are returned for the
date fields.
Note: Some sites have reported problems when using the file-access tests ("-r", "-w", and "-x") on files accessed via
DEC's DFS. Specifically, since DFS does not currently provide access to the extended file header of files on remote
volumes, attempts to examine the ACL fail, and the file tests will return false, with $! indicating that the file
does not exist. You can use "stat" on these files, since that checks UIC-based protection only, and then manually
check the appropriate bits, as defined by your C compiler's stat.h, in the mode value it returns, if you need an
approximation of the file's protections.
backticks
Backticks create a subprocess, and pass the enclosed string to it for execution as a DCL command. Since the
subprocess is created directly via "lib$spawn()", any valid DCL command string may be specified.
binmode FILEHANDLE
The "binmode" operator will attempt to insure that no translation of carriage control occurs on input from or output
to this filehandle. Since this involves reopening the file and then restoring its file position indicator, if this
function returns FALSE, the underlying filehandle may no longer point to an open file, or may point to a different
position in the file than before "binmode" was called.
Note that "binmode" is generally not necessary when using normal filehandles; it is provided so that you can control
I/O to existing record-structured files when necessary. You can also use the "vmsfopen" function in the VMS::Stdio
extension to gain finer control of I/O to files and devices with different record structures.
crypt PLAINTEXT, USER
The "crypt" operator uses the "sys$hash_password" system service to generate the hashed representation of PLAINTEXT.
If USER is a valid username, the algorithm and salt values are taken from that user's UAF record. If it is not, then
the preferred algorithm and a salt of 0 are used. The quadword encrypted value is returned as an 8-character string.
The value returned by "crypt" may be compared against the encrypted password from the UAF returned by the "getpw*"
functions, in order to authenticate users. If you're going to do this, remember that the encrypted password in the
UAF was generated using uppercase username and password strings; you'll have to upcase the arguments to "crypt" to
insure that you'll get the proper value:
sub validate_passwd {
my($user,$passwd) = @_;
my($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 $? status values are ones
that would cause the native status to be interpreted as being what VMS classifies as SEVERE_ERROR severity for DCL
error handling.
When "PERL_VMS_POSIX_EXIT" is active (see "$?" 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.
dump
Rather than causing Perl to abort and dump core, the "dump" operator invokes the VMS debugger. If you continue to
execute the Perl program under the debugger, control will be transferred to the label specified as the argument to
"dump", or, if no label was specified, back to the beginning of the program. All other state of the program (e.g.
values of variables, open file handles) are not affected by calling "dump".
exec LIST
A call to "exec" will cause Perl to exit, and to invoke the command given as an 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.
fork
While in principle the "fork" operator could be implemented via (and with the same rather severe limitations as) the
CRTL "vfork()" routine, and while some internal 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.
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. 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 $quota item is not used.
gmtime
The "gmtime" operator will function properly if you have a working CRTL "gmtime()" routine, or if the logical name
SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds which must be added to UTC to yield local time. (This
logical name is defined automatically if you are running a version of VMS with built-in UTC support.) If 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 $EXIT. Generally speaking,
"kill" follows the behavior of the CRTL's "kill()" function, but unlike that function can be called from within a
signal handler. Also, unlike the "kill" in some versions of the CRTL, Perl's "kill" checks the validity of the
signal passed in and returns an error rather than attempting to send an unrecognized signal.
Also, negative signal values don't do anything special under VMS; they're just converted to the corresponding
positive value.
qx//
See the entry on "backticks" above.
select (system call)
If Perl was not built with socket support, the system call version of "select" is not available at all. If socket
support is present, then the system call version of "select" functions only for file descriptors attached to sockets.
It will not provide information about regular files or pipes, since the CRTL "select()" routine does not provide this
functionality.
stat EXPR
Since VMS keeps track of files according to a different scheme than Unix, it's not really possible to represent the
file's ID in the "st_dev" and "st_ino" fields of a "struct stat". Perl tries its best, though, and the values it
uses are pretty unlikely to be the same for two different files. We can't guarantee this, though, so caveat
scriptor.
system LIST
The "system" operator creates a subprocess, and passes its arguments to the subprocess for execution as a DCL
command. Since the subprocess is created directly via "lib$spawn()", any valid DCL command string may be specified.
If the string begins with '@', it is treated as a DCL command unconditionally. Otherwise, if the first token
contains a character used as a delimiter in file specification (e.g. ":" or "]"), an attempt is made to expand it
using a default type of .Exe and the process defaults, and if successful, the resulting file is invoked via "MCR".
This allows you to invoke an image directly simply by passing the file specification to "system", a common Unixish
idiom. If the token has no file type, and matches a file with null type, then an attempt is made to determine
whether the file is an executable image which should be invoked using "MCR" or a text file which should be passed to
DCL as a command procedure.
If LIST consists of the empty string, "system" spawns an interactive DCL subprocess, in the same fashion as typing
SPAWN at the DCL prompt.
Perl waits for the subprocess to complete before continuing execution in the current process. As described in
perlfunc, the return value of "system" is a fake "status" which follows POSIX semantics unless the pragma "use vmsish
'status'" is in effect; see the description of $? in this document for more detail.
time
The value returned by "time" is the offset in seconds from 01-JAN-1970 00:00:00 (just like the CRTL's times()
routine), in order to make life easier for code coming in from the POSIX/Unix world.
times
The array returned by the "times" operator is divided up according to the same rules the CRTL "times()" routine.
Therefore, the "system time" elements will always be 0, since there is no difference between "user time" and "system"
time under VMS, and the time accumulated by a subprocess may or may not appear separately in the "child time" field,
depending on whether times keeps track of subprocesses separately. Note 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 $Config{'d_unlink_all_versions'} is "define", then "unlink" will delete all versions of a file on the first
call.)
"unlink" will delete a file if at all possible, even if it requires changing file protection (though it won't try to
change the protection of the parent directory). You can tell whether you've got explicit delete access to a file by
using the "VMS::Filespec::candelete" operator. For instance, in order to delete only files to which you have delete
access, you could say something like
sub safe_unlink {
my($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.
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 $?. If PID is a subprocess created in some other way (e.g. SPAWNed before Perl was
invoked), "waitpid" will simply check once per second whether the process has completed, and return when it has. (If
PID specifies a process that isn't a subprocess of the current process, and you invoked Perl with the "-w" switch, a
warning will be issued.)
Returns PID on success, -1 on error. The FLAGS argument is ignored in all cases.
Perl variables
The following VMS-specific information applies to the indicated "special" Perl variables, in addition to the general
information in perlvar. Where there is a conflict, this information takes precedence.
%ENV
The operation of the %ENV array depends on the translation of the logical name PERL_ENV_TABLES. If defined, it
should be a search list, each element of which specifies a location for %ENV elements. If you tell Perl to read or
set the element "$ENV{"name"}", then Perl uses the translations of PERL_ENV_TABLES as follows:
CRTL_ENV
This string tells Perl to consult the CRTL's internal "environ" array of key-value pairs, using name as the key.
In most cases, this contains only a few keys, but if Perl was invoked via the C "exec[lv]e()" function, as is the
case for CGI processing by some HTTP servers, then the "environ" array may have been populated by the calling
program.
CLISYM_[LOCAL]
A string beginning with "CLISYM_"tells Perl to consult the CLI's symbol tables, using name as the name of the
symbol. When reading an element of %ENV, the local symbol table is scanned first, followed by the global symbol
table.. The 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.
In all operations on %ENV, the key string is treated as if it were entirely uppercase, regardless of the case
actually specified in the Perl expression.
When an element of %ENV is read, the locations to which PERL_ENV_TABLES points are checked in order, and the value
obtained from the first successful lookup is returned. If the name of the %ENV element contains a semi-colon, it and
any characters after it are removed. These are ignored when the CRTL "environ" array or a CLI symbol table is
consulted. However, the name is looked up in a logical name table, the suffix after the semi-colon is treated as the
translation index to be used for the lookup. This lets you look up successive values for search list logical names.
For instance, if you say
$ Define STORY once,upon,a,time,there,was
$ perl -e "for ($i = 0; $i <= 6; $i++) " -
_$ -e "{ print $ENV{'story;'.$i},' '}"
Perl will print "ONCE UPON A TIME THERE WAS", assuming, of course, that PERL_ENV_TABLES is set up so that the logical
name "story" is found, rather than a CLI symbol or CRTL "environ" element with the same name.
When an element of %ENV is set to a defined string, the corresponding definition is made in the location to which the
first translation of PERL_ENV_TABLES points. If this causes a logical name to be created, it is defined in
supervisor mode. (The same is done if an existing logical name was defined in executive or kernel mode; an 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 00) character, since a logical name cannot translate to a zero-length
string. (This restriction does not apply to CLI symbols or CRTL "environ" values; they are set to the empty string.)
An element of the CRTL "environ" array can be set only if your copy of Perl knows about the CRTL's "setenv()"
function. (This is present only in some versions of the DECCRTL; check $Config{d_setenv} to see whether your copy of
Perl was built with a CRTL that has this function.)
When an element of %ENV is set to "undef", the element is looked up as if it were being read, and if it is found, it
is deleted. (An item "deleted" from the CRTL "environ" array is set to the empty string; this can only be done if
your copy of Perl knows about the CRTL "setenv()" function.) Using "delete" to remove an element from %ENV has a
similar effect, but after the element is deleted, another attempt is made to look up the element, so an inner-mode
logical name or a name in another location will replace the logical name just deleted. In either case, only the
first value found searching PERL_ENV_TABLES is altered. It is not possible at present to define a search list
logical name via %ENV.
The element $ENV{DEFAULT} is special: when read, it returns Perl's current default device and directory, and when
set, it resets them, regardless of the definition of PERL_ENV_TABLES. It cannot be cleared or deleted; attempts to
do so are silently ignored.
Note that if you want to pass on any elements of the C-local environ array to a subprocess which isn't started by
fork/exec, or isn't running a C program, you can "promote" them to logical names in the current process, which will
then be inherited by all subprocesses, by saying
foreach my $key (qw[C-local keys you want promoted]) {
my $temp = $ENV{$key}; # read from C-local array
$ENV{$key} = $temp; # and define as logical name
}
(You can't just say $ENV{$key} = $ENV{$key}, since the Perl optimizer is smart enough to elide the expression.)
Don't try to clear %ENV by saying "%ENV = ();", it will throw a fatal error. This is equivalent to doing the
following from DCL:
DELETE/LOGICAL *
You can imagine how bad things would be if, for example, the SYS$MANAGER or SYS$SYSTEM logical names were deleted.
At present, the first time you iterate over %ENV using "keys", or "values", you will incur a time penalty as all
logical names are read, in order to fully populate %ENV. Subsequent iterations will not reread logical names, so
they won't be as slow, but they also won't reflect any changes to logical name tables caused by other programs.
You do need to be careful with the logical names representing process-permanent files, such as "SYS$INPUT" and
"SYS$OUTPUT". The translations for these logical names are prepended with a two-byte binary value (0x1B 0x00) that
needs to be stripped off if you wantto use it. (In previous versions of Perl it wasn't possible to get the values of
these logical names, as the null byte acted as an end-of-string marker)
$! The string value of $! is that returned by the CRTL's strerror() function, so it will include the VMS message for
VMS-specific errors. The numeric value of $! is the value of "errno", except if errno is EVMSERR, in which case $!
contains the value of vaxc$errno. Setting $! always sets errno to the value specified. If this value is EVMSERR,
it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so that the string value of $! won't reflect the VMS error message
from before $! was set.
$^E This variable provides direct access to VMS status values in vaxc$errno, which are often more specific than the
generic Unix-style error messages in $!. Its numeric value is the value of vaxc$errno, and its string value is the
corresponding VMS message string, as retrieved by sys$getmsg(). Setting $^E sets vaxc$errno to the value specified.
While Perl attempts to keep the vaxc$errno value to be current, if errno is not EVMSERR, it may not be from the
current operation.
$? The "status value" returned in $? is synthesized from the actual exit status of the subprocess in a way that
approximates POSIX wait(5) semantics, in order to allow Perl programs to portably test for successful completion of
subprocesses. The low order 8 bits of $? are always 0 under VMS, since the termination status of a process may or
may not have been generated by an exception.
The next 8 bits contain the termination status of the program.
If the child process follows the convention of C programs compiled with the _POSIX_EXIT macro set, the status value
will contain the actual value of 0 to 255 returned by that program on a normal exit.
With the _POSIX_EXIT macro set, the Unix exit value of zero is represented as a VMS native status of 1, and the Unix
values from 2 to 255 are encoded by the equation:
VMS_status = 0x35a000 + (unix_value * 8) + 1.
And in the special case of Unix value 1 the encoding is:
VMS_status = 0x35a000 + 8 + 2 + 0x10000000.
For other termination statuses, the severity portion of the subprocess's exit status is used: if the severity was
success or informational, these bits are all 0; if the severity was warning, they contain a value of 1; if the
severity was error or fatal error, they contain the actual severity bits, which turns out to be a value of 2 for
error and 4 for severe_error. Fatal is another term for the severe_error status.
As a result, $? will always be zero if the subprocess's exit status indicated successful completion, and non-zero if
a warning or error occurred or a program compliant with encoding _POSIX_EXIT values was run and set a status.
How can you tell the difference between a non-zero status that is the result of a VMS native error status or an
encoded Unix status? You can not unless you look at the ${^CHILD_ERROR_NATIVE} value. The ${^CHILD_ERROR_NATIVE}
value returns the actual VMS status value and check the severity bits. If the severity bits are equal to 1, then if
the numeric value for $? is between 2 and 255 or 0, then $? accurately reflects a value passed back from a Unix
application. If $? is 1, and the severity bits indicate a VMS error (2), then $? is from a Unix application exit
value.
In practice, Perl scripts that call programs that return _POSIX_EXIT type status values will be expecting those
values, and programs that call traditional VMS programs will either be expecting the previous behavior or just
checking for a non-zero status.
And success is always the value 0 in all behaviors.
When the actual VMS termination status of the child is an error, internally the $! value will be set to the closest
Unix errno value to that error so that Perl scripts that test for error messages will see the expected Unix style
error message instead of a VMS message.
Conversely, when setting $? in an END block, an attempt is made to convert the POSIX value into a native status
intelligible to the operating system upon exiting Perl. What this boils down to is that setting $? to zero results
in the generic success value SS$_NORMAL, and setting $? to a non-zero value results in the generic failure status
SS$_ABORT. See also "exit" in perlport.
With the "PERL_VMS_POSIX_EXIT" logical name defined as "ENABLE", setting $? will cause the new value to be encoded
into $^E so that either the original parent or child exit status values
0 to 255 can be automatically recovered by C programs expecting _POSIX_EXIT behavior. If both a parent and a child
exit value are non-zero, then it will be assumed that this is actually a VMS native status value to be passed
through. The special value of 0xFFFF is almost a NOOP as it will cause the current native VMS status in the C
library to become the current native Perl VMS status, and is handled this way as it is known to not be a valid native
VMS status value. It is recommend that only values in the range of normal Unix parent or child status numbers, 0 to
255 are used.
The pragma "use vmsish 'status'" makes $? reflect the actual VMS exit status instead of the default emulation of
POSIX status described above. This pragma also disables the conversion of non-zero values to SS$_ABORT when setting
$? in an END block (but zero will still be converted to SS$_NORMAL).
Do not use the pragma "use vmsish 'status'" with "PERL_VMS_POSIX_EXIT" enabled, as they are at times requesting
conflicting actions and the consequence of ignoring this advice will be undefined to allow future improvements in the
POSIX exit handling.
In general, with "PERL_VMS_POSIX_EXIT" enabled, more detailed information will be availble in the exit status for DCL
scripts or other native VMS tools, and will give the expected information for Posix programs. It has not been made
the default in order to preserve backward compatibility.
N.B. Setting "DECC$FILENAME_UNIX_REPORT" implicitly enables "PERL_VMS_POSIX_EXIT".
$| Setting $| for an I/O stream causes data to be flushed all the way to disk on each write (i.e. not just to the
underlying RMS buffers for a file). In other words, it's equivalent to calling fflush() and fsync() from C.
Standard modules with VMS-specific differences
SDBM_File
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.
AUTHOR
Charles Bailey baileyATcor.edu Craig Berry craigberryATmac.com Dan Sugalski danATsidhe.org John Malmberg
wb8tywATqsl.net
perl v5.12.4 2011-06-07 PERLVMS(1)
