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 vmsperl@genetics.upenn.edu.

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 perlapi 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 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

N.B. The procedure by which extensions are built and tested creates several levels (at least 4) under the directory in which the extension's source files live. For this reason, you shouldn't nest the source directory too deeply in your directory structure, lest you eccedd 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.Auto.Arch.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 .). However, it can be manually placed in any of several locations: - the [.Lib.Auto.Extname] subdirectory of one of the directories in @INC, 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.

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..

File specifications

We have tried to make Perl aware of both VMS-style and Unix- style file specifications wherever possible. You may use either style, or both, on the command line and in scripts, but you may not combine the two styles within a single fle specfication. Filenames are, of course, still case- insensitive. For consistency, most Perl routines return filespecs using lower case latters only, regardless of the case used in the arguments passed to them. (This is true only when running under VMS; Perl respects the case- sensitivity of OSs like Unix.)

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

Command line redirection

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, and 2>>file appends stderr to file.

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

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

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 passed directly to lib$spawn as the command to execute. In this case, Perl will wait for the subprocess to complete before continuing.

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..

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 the file version only if one was present in the input filespec.

PERL5LIB and PERLLIB

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

%ENV

Reading the elements of the %ENV array returns the translation of the logical name specified by the key, according to the normal search order of access modes and logical name tables. If you append a semicolon to the logical name, followed by an integer, that integer is used as the translation index for the logical name, so that you can 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 $ENV{'foo'.$i},' '}"

Perl will print ONCE UPON A TIME THERE WAS.

The %ENV keys home, path,term, and user return the CRTL "environment variables" of the same names, if these logical names are not defined. The key default returns the current default device and directory specification, regardless of whether there is a logical name DEFAULT defined..

Setting an element of %ENV defines a supervisor-mode logical name in the process logical name table. Undefing or deleteing an element of %ENV deletes the equivalent user- mode or supervisor-mode logical name from the process logical name table. If you use undef, the %ENV element remains empty. If you use delete, another attempt is made at logical name translation after the deletion, so an inner-mode logical name or a name in another logical name table will replace the logical name just deleted. It is not possible at present to define a search list logical name via %ENV.

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.

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

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

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

The following functions may or may not be implemented, depending on what type of socket support you've built into your copy of Perl: accept, bind, connect, getpeername, gethostbyname, getnetbyname, getprotobyname, getservbyname, gethostbyaddr, getnetbyaddr, getprotobynumber, getservbyport, gethostent, getnetent, getprotoent, getservent, sethostent, setnetent, setprotoent, setservent, endhostent, endnetent, endprotoent, endservent, getsockname, getsockopt, listen, recv, select(system call)*, send, setsockopt, shutdown, socket

File tests

The tests -b, -B, -c, -C, -d, -e, -f, -o, -M, -s, -S, -t, -T, and -z work as advertised. The return values for -r, -w, and -x tell you whether you can actually access the file; this may not reflect the UIC-based file protections. Since real and effective UIC don't differ under VMS, -O, -R, -W, and -X are equivalent to -o, -r, -w, and -x. Similarly, several other tests, including -A, -g, -k, -l, -p, and -u, aren't particularly 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.

binmode FILEHANDLE

The binmode operator has no effect under VMS. It will return TRUE whenever called, but will not affect I/O operations on the filehandle given as its argument.

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;
}

exec LIST

The exec operator behaves in one of two different ways. If called after a call to fork, it will invoke the CRTL execv() routine, passing its arguments to the subprocess created by fork for execution. In this case, it is subject to all limitations that affect execv(). (In particular, this usually means that the command executed in the subprocess must be an image compiled from C source code, and that your options for passing file descriptors and signal handlers to the subprocess are limited.)

If the call to exec does not follow a call to fork, it will cause Perl to exit, and to invoke the command given as an argument to exec via lib$do_command. If the argument begins with a '$' (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.

You can use exec in both ways within the same script, as long as you call fork and exec in pairs. Perl keeps track of how many times fork and exec have been called, and will call the CRTL execv() routine if there have previously been more calls to fork than to exec.

fork

The fork operator works in the same way as the CRTL vfork() routine, which is quite different under VMS than under Unix. Specifically, while fork returns 0 after it is called and the subprocess PID after exec is called, in both cases the thread of execution is within the parent process, so there is no opportunity to perform operations in the subprocess before calling exec.

In general, the use of fork and exec to create subprocess is not recommended under VMS; wherever possible, use the system operator or piped filehandles instead.

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

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

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 LIST consists of the empty string, system spawns an interactive DCL subprocess, in the same fashion as typiing SPAWN at the DCL prompt. Perl waits for the subprocess to complete before continuing execution in the current process.

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 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 suprocesses 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; } Finally, if unlink has to change the file protection to delete the file, and you interrupt it in midstream, the file may be left intact, but with a changed ACL allowing you delete access.

utime LIST

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

waitpid PID,FLAGS

If PID is a subprocess started by a piped open, waitpid will wait for that subprocess, and return its final status value. If PID is a subprocess created in some other way (e.g. SPAWNed before Perl was invoked), or is not a subprocess of the current process, waitpid will check once per second whether the process has completed, and when it has, will return 0. (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.)

The FLAGS argument is ignored in all cases.

Revision date

This document was last updated on 16-Dec-1994, for Perl 5, patchlevel 2.

AUTHOR

Charles Bailey bailey@genetics.upenn.edu

cpanm lib

perl -MCPAN -e shell
install lib