perlvms - VMS-specific documentation for Perl
Gathered below are notes describing details of Perl 5's behavior on VMS. They are a supplement to the regular Perl 5 documentation, so we have focussed on the ways in which Perl 5 functions differently under VMS than it does under Unix, and on the interactions between Perl and the rest of the operating system. We haven't tried to duplicate complete descriptions of Perl features from the main Perl documentation, which can be found in the [.pod] subdirectory of the Perl distribution.
We hope these notes will save you from confusion and lost sleep when writing Perl scripts on VMS. If you find we've missed something you think should appear here, please don't hesitate to drop a line to vmsperl@genetics.upenn.edu.
Directions for building and installing Perl 5 can be found in the file README.vms in the main source directory of the Perl distribution..
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 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 the perlxs manpage 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.
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).
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
[.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: - 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.
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 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.
Filenames are, of course, still case-insensitive. For consistency, most Perl routines return filespecs using lower case letters 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.
File specifications containing wildcards are allowed both on the command line and within Perl globs (e.g. <C<*.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 contain the file version only if one was present in the input filespec.
Input and output pipes to Perl filehandles are supported; the ``file name'' is passed to lib$spawn() for asynchronous execution. You should be careful to close any pipes you have opened in a Perl script, lest you leave any ``orphaned'' subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose output is used as the return value of the expression. The string between the backticks is passed directly to lib$spawn as the command to execute. In this case, Perl will wait for the subprocess to complete before continuing.
The PERL5LIB and PERLLIB logical names work as documented the perl manpage, except that the element separator is '|' instead of ':'. The directory specifications may use either VMS or Unix syntax.
Perl for VMS supports redirection of input and output on the command line, using a subset of Bourne shell syntax:
<F<file> reads stdin from F<file>,
>F<file> writes stdout to F<file>,
>>F<file> appends stdout to F<file>,
2>F<file> writes stderr to F<file>, and
2>>F<file> appends stderr to F<file>.
In addition, output may be piped to a subprocess, using the character '|'. Anything after this character on the command line is passed to a subprocess for execution; the subprocess takes the output of Perl as its input.
Finally, if the command line ends with '&', the entire command is run in the background as an asynchronous subprocess.
The following command line switches behave differently under VMS than described in the perlrun manpage. Note also that in order to pass uppercase switches to Perl, you need to enclose them in double-quotes on the command line, since the CRTL downcases all unquoted strings.
-i switch is present but no extension for a backup copy is given, then inplace
editing creates a new version of a file; the existing copy is not deleted.
(Note that if an extension is given, an existing file is renamed to the
backup file, as is the case under other operating systems, so it does not
remain as a previous version under the original filename.)
-S switch is present and the script name does not contain a directory, then Perl translates the logical name
DCL$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 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.
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, 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, 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
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 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
-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.
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
$! indicating that the file does not exist. You can use stat on these files, since that checks UIC-based protection only, and then manually check the appropriate bits, as defined by your
C compiler's
stat.h, in the mode value it returns, if you need an approximation of the file's
protections.
lib$spawn(), any valid
DCL command string may be specified.
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.
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;
}
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.
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.
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.
$DELPRC system service 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
$FORCEX, which is ignored by supervisor-mode images like
DCL.)
Also, negative signal values don't do anything special under VMS; they're just converted to the corresponding positive value.
backticks above.
st_dev and st_ino fields of a struct stat. Perl tries its best, though, and the values it uses are pretty unlikely
to be the same for two different files. We can't guarantee this, though, so
caveat scriptor.
lib$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. As described in the perlfunc manpage, the return value of system is a fake ``status'' which follows
POSIX semantics; see the description of $? in this document for more detail. The actual
VMS exit status of the subprocess is available in $^S (as long as you haven't used another Perl function that resets $? and $^S in the meantime).
times() routine), in order to make life easier for code coming in from the POSIX/Unix world.
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.
-w switch, a warning will be issued.)
The FLAGS argument is ignored in all cases.
The following VMS-specific information applies to the indicated ``special'' Perl variables, in addition to the general information in the perlvar manpage. Where there is a conflict, this infrmation takes precedence.
%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 $ENV{'story;'.$i},' '}"
Perl will print ONCE UPON A TIME THERE WAS.
The key default returns the current default device and directory specification, regardless of whether there is a logical name
DEFAULT defined. If you try to read an element of %ENV for which there is no corresponding logical name, and for which no corresponding
CLI symbol exists (this is to identify ``blocking'' symbols only; to manipulate
CLI symbols, see
DCLSym) then the key will be looked up in the CRTL-local environment array, and
the corresponding value, if any returned. This lets you get at C-specific
keys like home, path,term, and
user, as well as other keys which may have been passed directly into the C-specific array if Perl was called from another
C program using the version of
execve() or
execle() present in recent revisions of the
DECCRTL.
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. It is also not possible to delete an element from the C-local environ array.
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.)
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. The
each
operator is special: it returns each element already in
%ENV, but doesn't go out and look for more. Therefore,
if you've previously used keys or values, you'll see all the logical names visible to your process, and if not,
you'll see only the names you've looked up so far. (This is a consequence
of the way each is implemented now, and it may change in the future, so it wouldn't be a
good idea to rely on it too much.)
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.
$! 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.
$!. Its numeric value is the value of vaxc$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.
$? 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 are derived
from severity portion of the subprocess' exit status: if the severity was
success or informational, these bits are all 0; otherwise, they contain the
severity value shifted left one bit. As a result, $? will always be zero if the subprocess' exit status indicated successful completion, and non-zero if a warning or error occurred. The actual
VMS exit status may be found in
$^S (q.v.).
$?, no manipulation is done to make this look like a
POSIX
wait(5) value, so it may be treated as a normal
VMS status value.
$| 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.
SDBM_File works peroperly 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.
This document was last updated on 26-Feb-1998, for Perl 5, patchlevel 5.
Charles Bailey bailey@cor.newman.upenn.edu
Last revision by Dan Sugalski sugalskd@ous.edu
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.