3 perlvms - VMS-specific documentation for Perl
7 Gathered below are notes describing details of Perl 5's
8 behavior on VMS. They are a supplement to the regular Perl 5
9 documentation, so we have focussed on the ways in which Perl
10 5 functions differently under VMS than it does under Unix,
11 and on the interactions between Perl and the rest of the
12 operating system. We haven't tried to duplicate complete
13 descriptions of Perl features from the main Perl
14 documentation, which can be found in the F<[.pod]>
15 subdirectory of the Perl distribution.
17 We hope these notes will save you from confusion and lost
18 sleep when writing Perl scripts on VMS. If you find we've
19 missed something you think should appear here, please don't
20 hesitate to drop a line to vmsperl@perl.org.
24 Directions for building and installing Perl 5 can be found in
25 the file F<README.vms> in the main source directory of the
28 =head1 Organization of Perl Images
32 During the installation process, three Perl images are produced.
33 F<Miniperl.Exe> is an executable image which contains all of
34 the basic functionality of Perl, but cannot take advantage of
35 Perl extensions. It is used to generate several files needed
36 to build the complete Perl and various extensions. Once you've
37 finished installing Perl, you can delete this image.
39 Most of the complete Perl resides in the shareable image
40 F<PerlShr.Exe>, which provides a core to which the Perl executable
41 image and all Perl extensions are linked. You should place this
42 image in F<Sys$Share>, or define the logical name F<PerlShr> to
43 translate to the full file specification of this image. It should
44 be world readable. (Remember that if a user has execute only access
45 to F<PerlShr>, VMS will treat it as if it were a privileged shareable
46 image, and will therefore require all downstream shareable images to be
50 Finally, F<Perl.Exe> is an executable image containing the main
51 entry point for Perl, as well as some initialization code. It
52 should be placed in a public directory, and made world executable.
53 In order to run Perl with command line arguments, you should
54 define a foreign command to invoke this image.
56 =head2 Perl Extensions
58 Perl extensions are packages which provide both XS and Perl code
59 to add new functionality to perl. (XS is a meta-language which
60 simplifies writing C code which interacts with Perl, see
61 L<perlxs> for more details.) The Perl code for an
62 extension is treated like any other library module - it's
63 made available in your script through the appropriate
64 C<use> or C<require> statement, and usually defines a Perl
65 package containing the extension.
67 The portion of the extension provided by the XS code may be
68 connected to the rest of Perl in either of two ways. In the
69 B<static> configuration, the object code for the extension is
70 linked directly into F<PerlShr.Exe>, and is initialized whenever
71 Perl is invoked. In the B<dynamic> configuration, the extension's
72 machine code is placed into a separate shareable image, which is
73 mapped by Perl's DynaLoader when the extension is C<use>d or
74 C<require>d in your script. This allows you to maintain the
75 extension as a separate entity, at the cost of keeping track of the
76 additional shareable image. Most extensions can be set up as either
79 The source code for an extension usually resides in its own
80 directory. At least three files are generally provided:
81 I<Extshortname>F<.xs> (where I<Extshortname> is the portion of
82 the extension's name following the last C<::>), containing
83 the XS code, I<Extshortname>F<.pm>, the Perl library module
84 for the extension, and F<Makefile.PL>, a Perl script which uses
85 the C<MakeMaker> library modules supplied with Perl to generate
86 a F<Descrip.MMS> file for the extension.
88 =head2 Installing static extensions
90 Since static extensions are incorporated directly into
91 F<PerlShr.Exe>, you'll have to rebuild Perl to incorporate a
92 new extension. You should edit the main F<Descrip.MMS> or F<Makefile>
93 you use to build Perl, adding the extension's name to the C<ext>
94 macro, and the extension's object file to the C<extobj> macro.
95 You'll also need to build the extension's object file, either
96 by adding dependencies to the main F<Descrip.MMS>, or using a
97 separate F<Descrip.MMS> for the extension. Then, rebuild
98 F<PerlShr.Exe> to incorporate the new code.
100 Finally, you'll need to copy the extension's Perl library
101 module to the F<[.>I<Extname>F<]> subdirectory under one
102 of the directories in C<@INC>, where I<Extname> is the name
103 of the extension, with all C<::> replaced by C<.> (e.g.
104 the library module for extension Foo::Bar would be copied
105 to a F<[.Foo.Bar]> subdirectory).
107 =head2 Installing dynamic extensions
109 In general, the distributed kit for a Perl extension includes
110 a file named Makefile.PL, which is a Perl program which is used
111 to create a F<Descrip.MMS> file which can be used to build and
112 install the files required by the extension. The kit should be
113 unpacked into a directory tree B<not> under the main Perl source
114 directory, and the procedure for building the extension is simply
116 $ perl Makefile.PL ! Create Descrip.MMS
117 $ mmk ! Build necessary files
118 $ mmk test ! Run test code, if supplied
119 $ mmk install ! Install into public Perl tree
121 I<N.B.> The procedure by which extensions are built and
122 tested creates several levels (at least 4) under the
123 directory in which the extension's source files live.
124 For this reason if you are running a version of VMS prior
125 to V7.1 you shouldn't nest the source directory
126 too deeply in your directory structure lest you exceed RMS'
127 maximum of 8 levels of subdirectory in a filespec. (You
128 can use rooted logical names to get another 8 levels of
129 nesting, if you can't place the files near the top of
130 the physical directory structure.)
132 VMS support for this process in the current release of Perl
133 is sufficient to handle most extensions. However, it does
134 not yet recognize extra libraries required to build shareable
135 images which are part of an extension, so these must be added
136 to the linker options file for the extension by hand. For
137 instance, if the F<PGPLOT> extension to Perl requires the
138 F<PGPLOTSHR.EXE> shareable image in order to properly link
139 the Perl extension, then the line C<PGPLOTSHR/Share> must
140 be added to the linker options file F<PGPLOT.Opt> produced
141 during the build process for the Perl extension.
143 By default, the shareable image for an extension is placed in
144 the F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
145 installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
146 F<VMS_AXP>, and I<Extname> is the name of the extension, with
147 each C<::> translated to C<.>). (See the MakeMaker documentation
148 for more details on installation options for extensions.)
149 However, it can be manually placed in any of several locations:
155 the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
156 of one of the directories in C<@INC> (where I<PVers>
157 is the version of Perl you're using, as supplied in C<$]>,
158 with '.' converted to '_'), or
162 one of the directories in C<@INC>, or
166 a directory which the extensions Perl library module
167 passes to the DynaLoader when asking it to map
168 the shareable image, or
172 F<Sys$Share> or F<Sys$Library>.
176 If the shareable image isn't in any of these places, you'll need
177 to define a logical name I<Extshortname>, where I<Extshortname>
178 is the portion of the extension's name after the last C<::>, which
179 translates to the full file specification of the shareable image.
181 =head1 File specifications
185 We have tried to make Perl aware of both VMS-style and Unix-
186 style file specifications wherever possible. You may use
187 either style, or both, on the command line and in scripts,
188 but you may not combine the two styles within a single file
189 specification. VMS Perl interprets Unix pathnames in much
190 the same way as the CRTL (I<e.g.> the first component of
191 an absolute path is read as the device name for the
192 VMS file specification). There are a set of functions
193 provided in the C<VMS::Filespec> package for explicit
194 interconversion between VMS and Unix syntax; its
195 documentation provides more details.
197 Perl is now in the process of evolving to follow the setting of
198 the DECC$* feature logicals in the interpretation of UNIX pathnames.
199 This is still a work in progress.
201 For handling extended characters, and case sensitivity, as long as
202 DECC$POSIX_COMPLIANT_PATHNAMES, DECC$FILENAME_UNIX_REPORT, and
203 DECC$FILENAME_UNIX_ONLY are not set, then the older Perl behavior
204 for conversions of file specifications from UNIX to VMS is followed,
205 except that VMS paths with concealed rooted logicals are now
206 translated correctly to UNIX paths.
208 With those features set, then new routines may handle the translation,
209 because some of the rules are different. The presence of ./.../
210 in a UNIX path is no longer translated to the VMS [...]. It will
211 translate to [.^.^.^.]. To be compatible with what MakeMaker expects,
212 if a VMS path can not be translated to a UNIX path when unixify
213 is called, it is passed through unchanged. So unixify("[...]") will
216 The handling of extended characters will also be better with the
217 newer translation routines. But more work is needed to fully support
218 extended file syntax names. In particular, at this writing Pathtools
219 can not deal with directories containing some extended characters.
221 There are several ambiguous cases where a conversion routine can not
222 determine if an input filename is in UNIX format or in VMS format,
223 since now both VMS UNIX file specifications can have characters in
224 them that could be mistaken for syntax delimiters of the other type.
225 So some pathnames simply can not be used in a mode that allows either
226 type of pathname to be present.
228 Perl will tend to assume that an ambiguous filename is in UNIX format.
230 Allowing "." as a version delimiter is simply incompatible with
231 determining if a pathname is already VMS format or UNIX with the
232 extended file syntax. There is no way to know if "perl-5.8.6" that
233 TAR produces is a UNIX "perl-5.8.6" or a VMS "perl-5.8;6" when
234 passing it to unixify() or vmsify().
236 The DECC$FILENAME_UNIX_REPORT or the DECC$FILENAME_UNIX_ONLY logical
237 names control how Perl interprets filenames.
239 The DECC$FILENAME_UNIX_ONLY setting has not been tested at this time.
240 Perl uses traditional OpenVMS file specifications internally and in
241 the test harness, so this mode may have limited use, or require more
242 changes to make usable.
244 Everything about DECC$FILENAME_UNIX_REPORT should be assumed to apply
245 to DECC$FILENAME_UNIX_ONLY mode. The DECC$FILENAME_UNIX_ONLY differs
246 in that it expects all filenames passed to the C runtime to be already
249 Again, currently most of the core Perl modules have not yet been updated
250 to understand that VMS is not as limited as it use to be. Fixing that
251 is a work in progress.
253 The logical name DECC$POSIX_COMPLIANT_PATHNAMES is new with the
254 RMS Symbolic Link SDK. This version of Perl does not support it being set.
257 Filenames are case-insensitive on VAX, and on ODS-2 formatted
258 volumes on ALPHA and I64.
260 On ODS-5 volumes filenames are case preserved and on newer
261 versions of OpenVMS can be optionally case sensitive.
263 On ALPHA and I64, Perl is in the process of being changed to follow the
264 process case sensitivity setting to report if the file system is case
267 Perl programs should not assume that VMS is case blind, or that
268 filenames will be in lowercase.
270 Programs should use the File::Spec:case_tolerant setting to determine
271 the state, and not the $^O setting.
273 For consistency, when the above feature is clear and when not
274 otherwise overridden by DECC feature logicals, most Perl routines
275 return file specifications using lower case letters only,
276 regardless of the case used in the arguments passed to them.
277 (This is true only when running under VMS; Perl respects the
278 case-sensitivity of OSs like Unix.)
280 We've tried to minimize the dependence of Perl library
281 modules on Unix syntax, but you may find that some of these,
282 as well as some scripts written for Unix systems, will
283 require that you use Unix syntax, since they will assume that
284 '/' is the directory separator, I<etc.> If you find instances
285 of this in the Perl distribution itself, please let us know,
286 so we can try to work around them.
288 Also when working on Perl programs on VMS, if you need a syntax
289 in a specific operating system format, then you need to either
290 check the appropriate DECC$ feature logical, or call a conversion
291 routine to force it to that format.
293 =head2 Wildcard expansion
295 File specifications containing wildcards are allowed both on
296 the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>). If
297 the wildcard filespec uses VMS syntax, the resultant
298 filespecs will follow VMS syntax; if a Unix-style filespec is
299 passed in, Unix-style filespecs will be returned.
300 Similar to the behavior of wildcard globbing for a Unix shell,
301 one can escape command line wildcards with double quotation
302 marks C<"> around a perl program command line argument. However,
303 owing to the stripping of C<"> characters carried out by the C
304 handling of argv you will need to escape a construct such as
305 this one (in a directory containing the files F<PERL.C>, F<PERL.EXE>,
306 F<PERL.H>, and F<PERL.OBJ>):
308 $ perl -e "print join(' ',@ARGV)" perl.*
309 perl.c perl.exe perl.h perl.obj
311 in the following triple quoted manner:
313 $ perl -e "print join(' ',@ARGV)" """perl.*"""
316 In both the case of unquoted command line arguments or in calls
317 to C<glob()> VMS wildcard expansion is performed. (csh-style
318 wildcard expansion is available if you use C<File::Glob::glob>.)
319 If the wildcard filespec contains a device or directory
320 specification, then the resultant filespecs will also contain
321 a device and directory; otherwise, device and directory
322 information are removed. VMS-style resultant filespecs will
323 contain a full device and directory, while Unix-style
324 resultant filespecs will contain only as much of a directory
325 path as was present in the input filespec. For example, if
326 your default directory is Perl_Root:[000000], the expansion
327 of C<[.t]*.*> will yield filespecs like
328 "perl_root:[t]base.dir", while the expansion of C<t/*/*> will
329 yield filespecs like "t/base.dir". (This is done to match
330 the behavior of glob expansion performed by Unix shells.)
332 Similarly, the resultant filespec will contain the file version
333 only if one was present in the input filespec.
338 Input and output pipes to Perl filehandles are supported; the
339 "file name" is passed to lib$spawn() for asynchronous
340 execution. You should be careful to close any pipes you have
341 opened in a Perl script, lest you leave any "orphaned"
342 subprocesses around when Perl exits.
344 You may also use backticks to invoke a DCL subprocess, whose
345 output is used as the return value of the expression. The
346 string between the backticks is handled as if it were the
347 argument to the C<system> operator (see below). In this case,
348 Perl will wait for the subprocess to complete before continuing.
350 The mailbox (MBX) that perl can create to communicate with a pipe
351 defaults to a buffer size of 512. The default buffer size is
352 adjustable via the logical name PERL_MBX_SIZE provided that the
353 value falls between 128 and the SYSGEN parameter MAXBUF inclusive.
354 For example, to double the MBX size from the default within
355 a Perl program, use C<$ENV{'PERL_MBX_SIZE'} = 1024;> and then
356 open and use pipe constructs. An alternative would be to issue
359 $ Define PERL_MBX_SIZE 1024
361 before running your wide record pipe program. A larger value may
362 improve performance at the expense of the BYTLM UAF quota.
364 =head1 PERL5LIB and PERLLIB
366 The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
367 except that the element separator is '|' instead of ':'. The
368 directory specifications may use either VMS or Unix syntax.
372 =head2 I/O redirection and backgrounding
374 Perl for VMS supports redirection of input and output on the
375 command line, using a subset of Bourne shell syntax:
381 C<E<lt>file> reads stdin from C<file>,
385 C<E<gt>file> writes stdout to C<file>,
389 C<E<gt>E<gt>file> appends stdout to C<file>,
393 C<2E<gt>file> writes stderr to C<file>,
397 C<2E<gt>E<gt>file> appends stderr to C<file>, and
401 C<< 2>&1 >> redirects stderr to stdout.
405 In addition, output may be piped to a subprocess, using the
406 character '|'. Anything after this character on the command
407 line is passed to a subprocess for execution; the subprocess
408 takes the output of Perl as its input.
410 Finally, if the command line ends with '&', the entire
411 command is run in the background as an asynchronous
414 =head2 Command line switches
416 The following command line switches behave differently under
417 VMS than described in L<perlrun>. Note also that in order
418 to pass uppercase switches to Perl, you need to enclose
419 them in double-quotes on the command line, since the CRTL
420 downcases all unquoted strings.
422 On newer 64 bit versions of OpenVMS, a process setting now
423 controls if the quoting is needed to preserve the case of
424 command line arguments.
430 If the C<-i> switch is present but no extension for a backup
431 copy is given, then inplace editing creates a new version of
432 a file; the existing copy is not deleted. (Note that if
433 an extension is given, an existing file is renamed to the backup
434 file, as is the case under other operating systems, so it does
435 not remain as a previous version under the original filename.)
439 If the C<"-S"> or C<-"S"> switch is present I<and> the script
440 name does not contain a directory, then Perl translates the
441 logical name DCL$PATH as a searchlist, using each translation
442 as a directory in which to look for the script. In addition,
443 if no file type is specified, Perl looks in each directory
444 for a file matching the name specified, with a blank type,
445 a type of F<.pl>, and a type of F<.com>, in that order.
449 The C<-u> switch causes the VMS debugger to be invoked
450 after the Perl program is compiled, but before it has
451 run. It does not create a core dump file.
455 =head1 Perl functions
457 As of the time this document was last revised, the following
458 Perl functions were implemented in the VMS port of Perl
459 (functions marked with * are discussed in more detail below):
461 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
462 caller, chdir, chmod, chown, chomp, chop, chr,
463 close, closedir, cos, crypt*, defined, delete,
464 die, do, dump*, each, endpwent, eof, eval, exec*,
465 exists, exit, exp, fileno, getc, getlogin, getppid,
466 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
467 grep, hex, import, index, int, join, keys, kill*,
468 last, lc, lcfirst, length, local, localtime, log, m//,
469 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
470 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
471 qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
472 require, reset, return, reverse, rewinddir, rindex,
473 rmdir, s///, scalar, seek, seekdir, select(internal),
474 select (system call)*, setpwent, shift, sin, sleep,
475 sort, splice, split, sprintf, sqrt, srand, stat,
476 study, substr, sysread, system*, syswrite, tell,
477 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
478 undef, unlink*, unpack, untie, unshift, use, utime*,
479 values, vec, wait, waitpid*, wantarray, warn, write, y///
481 The following functions were not implemented in the VMS port,
482 and calling them produces a fatal error (usually) or
483 undefined behavior (rarely, we hope):
485 chroot, dbmclose, dbmopen, flock, fork*,
486 getpgrp, getpriority, getgrent, getgrgid,
487 getgrnam, setgrent, endgrent, ioctl, link, lstat,
488 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
489 semget, semop, setpgrp, setpriority, shmctl, shmget,
490 shmread, shmwrite, socketpair, symlink, syscall
492 The following functions are available on Perls compiled with Dec C
493 5.2 or greater and running VMS 7.0 or greater:
497 The following functions are available on Perls built on VMS 7.2 or
500 fcntl (without locking)
502 The following functions may or may not be implemented,
503 depending on what type of socket support you've built into
506 accept, bind, connect, getpeername,
507 gethostbyname, getnetbyname, getprotobyname,
508 getservbyname, gethostbyaddr, getnetbyaddr,
509 getprotobynumber, getservbyport, gethostent,
510 getnetent, getprotoent, getservent, sethostent,
511 setnetent, setprotoent, setservent, endhostent,
512 endnetent, endprotoent, endservent, getsockname,
513 getsockopt, listen, recv, select(system call)*,
514 send, setsockopt, shutdown, socket
516 The following function is available on Perls built on 64 bit OpenVMS 8.2
517 with hard links enabled on an ODS-5 formatted build disk. If someone with
518 an OpenVMS 7.3-1 system were to modify configure.com and test the results,
519 this feature can be brought back to OpenVMS 7.3-1 and later. Hardlinks
520 must be enabled on the build disk because if the build procedure sees
521 this feature enabled, it uses it.
525 The following functions are available on Perls built on 64 bit OpenVMS
526 8.2 and can be implemented on OpenVMS 7.3-2 if someone were to modify
527 configure.com and test the results. (While in the build, at the time
528 of this writing, they have not been specifically tested.)
530 getgrgid, getgrnam, getpwnam, getpwuid,
533 The following functions are available on Perls built on 64 bit OpenVMS 8.2
534 and later. (While in the build, at the time of this writing, they have
535 not been specifically tested.)
539 The following functions are expected to soon be available on Perls built
540 on 64 bit OpenVMS 8.2 or later with the RMS Symbolic link package. Use
541 of symbolic links at this time effectively requires the
542 DECC$POSIX_COMPLIANT_PATHNAMES to defined as 3, and operating in a
543 DECC$FILENAME_UNIX_REPORT mode.
545 lchown, link, lstat, readlink, symlink
550 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
551 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
552 advertised. The return values for C<-r>, C<-w>, and C<-x>
553 tell you whether you can actually access the file; this may
554 not reflect the UIC-based file protections. Since real and
555 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
556 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
557 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
558 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
559 VMS, and the values returned by these tests reflect whatever
560 your CRTL C<stat()> routine does to the equivalent bits in the
561 st_mode field. Finally, C<-d> returns true if passed a device
562 specification without an explicit directory (e.g. C<DUA1:>), as
563 well as if passed a directory.
565 There are DECC feature logicals AND ODS-5 volume attributes that
566 also control what values are returned for the date fields.
568 Note: Some sites have reported problems when using the file-access
569 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
570 Specifically, since DFS does not currently provide access to the
571 extended file header of files on remote volumes, attempts to
572 examine the ACL fail, and the file tests will return false,
573 with C<$!> indicating that the file does not exist. You can
574 use C<stat> on these files, since that checks UIC-based protection
575 only, and then manually check the appropriate bits, as defined by
576 your C compiler's F<stat.h>, in the mode value it returns, if you
577 need an approximation of the file's protections.
581 Backticks create a subprocess, and pass the enclosed string
582 to it for execution as a DCL command. Since the subprocess is
583 created directly via C<lib$spawn()>, any valid DCL command string
586 =item binmode FILEHANDLE
588 The C<binmode> operator will attempt to insure that no translation
589 of carriage control occurs on input from or output to this filehandle.
590 Since this involves reopening the file and then restoring its
591 file position indicator, if this function returns FALSE, the
592 underlying filehandle may no longer point to an open file, or may
593 point to a different position in the file than before C<binmode>
596 Note that C<binmode> is generally not necessary when using normal
597 filehandles; it is provided so that you can control I/O to existing
598 record-structured files when necessary. You can also use the
599 C<vmsfopen> function in the VMS::Stdio extension to gain finer
600 control of I/O to files and devices with different record structures.
602 =item crypt PLAINTEXT, USER
604 The C<crypt> operator uses the C<sys$hash_password> system
605 service to generate the hashed representation of PLAINTEXT.
606 If USER is a valid username, the algorithm and salt values
607 are taken from that user's UAF record. If it is not, then
608 the preferred algorithm and a salt of 0 are used. The
609 quadword encrypted value is returned as an 8-character string.
611 The value returned by C<crypt> may be compared against
612 the encrypted password from the UAF returned by the C<getpw*>
613 functions, in order to authenticate users. If you're
614 going to do this, remember that the encrypted password in
615 the UAF was generated using uppercase username and
616 password strings; you'll have to upcase the arguments to
617 C<crypt> to insure that you'll get the proper value:
619 sub validate_passwd {
620 my($user,$passwd) = @_;
622 if ( !($pwdhash = (getpwnam($user))[1]) ||
623 $pwdhash ne crypt("\U$passwd","\U$name") ) {
624 intruder_alert($name);
631 Rather than causing Perl to abort and dump core, the C<dump>
632 operator invokes the VMS debugger. If you continue to
633 execute the Perl program under the debugger, control will
634 be transferred to the label specified as the argument to
635 C<dump>, or, if no label was specified, back to the
636 beginning of the program. All other state of the program
637 (I<e.g.> values of variables, open file handles) are not
638 affected by calling C<dump>.
642 A call to C<exec> will cause Perl to exit, and to invoke the command
643 given as an argument to C<exec> via C<lib$do_command>. If the
644 argument begins with '@' or '$' (other than as part of a filespec),
645 then it is executed as a DCL command. Otherwise, the first token on
646 the command line is treated as the filespec of an image to run, and
647 an attempt is made to invoke it (using F<.Exe> and the process
648 defaults to expand the filespec) and pass the rest of C<exec>'s
649 argument to it as parameters. If the token has no file type, and
650 matches a file with null type, then an attempt is made to determine
651 whether the file is an executable image which should be invoked
652 using C<MCR> or a text file which should be passed to DCL as a
657 While in principle the C<fork> operator could be implemented via
658 (and with the same rather severe limitations as) the CRTL C<vfork()>
659 routine, and while some internal support to do just that is in
660 place, the implementation has never been completed, making C<fork>
661 currently unavailable. A true kernel C<fork()> is expected in a
662 future version of VMS, and the pseudo-fork based on interpreter
663 threads may be available in a future version of Perl on VMS (see
664 L<perlfork>). In the meantime, use C<system>, backticks, or piped
665 filehandles to create subprocesses.
673 These operators obtain the information described in L<perlfunc>,
674 if you have the privileges necessary to retrieve the named user's
675 UAF information via C<sys$getuai>. If not, then only the C<$name>,
676 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
677 the login directory in VMS syntax, while the C<$comment> item
678 contains the login directory in Unix syntax. The C<$gcos> item
679 contains the owner field from the UAF record. The C<$quota>
684 The C<gmtime> operator will function properly if you have a
685 working CRTL C<gmtime()> routine, or if the logical name
686 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
687 which must be added to UTC to yield local time. (This logical
688 name is defined automatically if you are running a version of
689 VMS with built-in UTC support.) If neither of these cases is
690 true, a warning message is printed, and C<undef> is returned.
694 In most cases, C<kill> is implemented via the CRTL's C<kill()>
695 function, so it will behave according to that function's
696 documentation. If you send a SIGKILL, however, the $DELPRC system
697 service is called directly. This insures that the target
698 process is actually deleted, if at all possible. (The CRTL's C<kill()>
699 function is presently implemented via $FORCEX, which is ignored by
700 supervisor-mode images like DCL.)
702 Also, negative signal values don't do anything special under
703 VMS; they're just converted to the corresponding positive value.
707 See the entry on C<backticks> above.
709 =item select (system call)
711 If Perl was not built with socket support, the system call
712 version of C<select> is not available at all. If socket
713 support is present, then the system call version of
714 C<select> functions only for file descriptors attached
715 to sockets. It will not provide information about regular
716 files or pipes, since the CRTL C<select()> routine does not
717 provide this functionality.
721 Since VMS keeps track of files according to a different scheme
722 than Unix, it's not really possible to represent the file's ID
723 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
724 tries its best, though, and the values it uses are pretty unlikely
725 to be the same for two different files. We can't guarantee this,
726 though, so caveat scriptor.
730 The C<system> operator creates a subprocess, and passes its
731 arguments to the subprocess for execution as a DCL command.
732 Since the subprocess is created directly via C<lib$spawn()>, any
733 valid DCL command string may be specified. If the string begins with
734 '@', it is treated as a DCL command unconditionally. Otherwise, if
735 the first token contains a character used as a delimiter in file
736 specification (e.g. C<:> or C<]>), an attempt is made to expand it
737 using a default type of F<.Exe> and the process defaults, and if
738 successful, the resulting file is invoked via C<MCR>. This allows you
739 to invoke an image directly simply by passing the file specification
740 to C<system>, a common Unixish idiom. If the token has no file type,
741 and matches a file with null type, then an attempt is made to
742 determine whether the file is an executable image which should be
743 invoked using C<MCR> or a text file which should be passed to DCL
744 as a command procedure.
746 If LIST consists of the empty string, C<system> spawns an
747 interactive DCL subprocess, in the same fashion as typing
748 B<SPAWN> at the DCL prompt.
750 Perl waits for the subprocess to complete before continuing
751 execution in the current process. As described in L<perlfunc>,
752 the return value of C<system> is a fake "status" which follows
753 POSIX semantics unless the pragma C<use vmsish 'status'> is in
754 effect; see the description of C<$?> in this document for more
759 The value returned by C<time> is the offset in seconds from
760 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
761 to make life easier for code coming in from the POSIX/Unix world.
765 The array returned by the C<times> operator is divided up
766 according to the same rules the CRTL C<times()> routine.
767 Therefore, the "system time" elements will always be 0, since
768 there is no difference between "user time" and "system" time
769 under VMS, and the time accumulated by a subprocess may or may
770 not appear separately in the "child time" field, depending on
771 whether L<times> keeps track of subprocesses separately. Note
772 especially that the VAXCRTL (at least) keeps track only of
773 subprocesses spawned using L<fork> and L<exec>; it will not
774 accumulate the times of subprocesses spawned via pipes, L<system>,
779 C<unlink> will delete the highest version of a file only; in
780 order to delete all versions, you need to say
784 You may need to make this change to scripts written for a
785 Unix system which expect that after a call to C<unlink>,
786 no files with the names passed to C<unlink> will exist.
787 (Note: This can be changed at compile time; if you
788 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
789 C<define>, then C<unlink> will delete all versions of a
790 file on the first call.)
792 C<unlink> will delete a file if at all possible, even if it
793 requires changing file protection (though it won't try to
794 change the protection of the parent directory). You can tell
795 whether you've got explicit delete access to a file by using the
796 C<VMS::Filespec::candelete> operator. For instance, in order
797 to delete only files to which you have delete access, you could
803 next unless VMS::Filespec::candelete($file);
804 $num += unlink $file;
809 (or you could just use C<VMS::Stdio::remove>, if you've installed
810 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
811 change the file protection to delete the file, and you interrupt it
812 in midstream, the file may be left intact, but with a changed ACL
813 allowing you delete access.
817 Since ODS-2, the VMS file structure for disk files, does not keep
818 track of access times, this operator changes only the modification
819 time of the file (VMS revision date).
821 =item waitpid PID,FLAGS
823 If PID is a subprocess started by a piped C<open()> (see L<open>),
824 C<waitpid> will wait for that subprocess, and return its final status
825 value in C<$?>. If PID is a subprocess created in some other way (e.g.
826 SPAWNed before Perl was invoked), C<waitpid> will simply check once per
827 second whether the process has completed, and return when it has. (If
828 PID specifies a process that isn't a subprocess of the current process,
829 and you invoked Perl with the C<-w> switch, a warning will be issued.)
831 Returns PID on success, -1 on error. The FLAGS argument is ignored
836 =head1 Perl variables
838 The following VMS-specific information applies to the indicated
839 "special" Perl variables, in addition to the general information
840 in L<perlvar>. Where there is a conflict, this information
847 The operation of the C<%ENV> array depends on the translation
848 of the logical name F<PERL_ENV_TABLES>. If defined, it should
849 be a search list, each element of which specifies a location
850 for C<%ENV> elements. If you tell Perl to read or set the
851 element C<$ENV{>I<name>C<}>, then Perl uses the translations of
852 F<PERL_ENV_TABLES> as follows:
858 This string tells Perl to consult the CRTL's internal C<environ>
859 array of key-value pairs, using I<name> as the key. In most cases,
860 this contains only a few keys, but if Perl was invoked via the C
861 C<exec[lv]e()> function, as is the case for CGI processing by some
862 HTTP servers, then the C<environ> array may have been populated by
867 A string beginning with C<CLISYM_>tells Perl to consult the CLI's
868 symbol tables, using I<name> as the name of the symbol. When reading
869 an element of C<%ENV>, the local symbol table is scanned first, followed
870 by the global symbol table.. The characters following C<CLISYM_> are
871 significant when an element of C<%ENV> is set or deleted: if the
872 complete string is C<CLISYM_LOCAL>, the change is made in the local
873 symbol table; otherwise the global symbol table is changed.
875 =item Any other string
877 If an element of F<PERL_ENV_TABLES> translates to any other string,
878 that string is used as the name of a logical name table, which is
879 consulted using I<name> as the logical name. The normal search
880 order of access modes is used.
884 F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
885 you make while Perl is running do not affect the behavior of C<%ENV>.
886 If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
887 first the logical name tables specified by F<LNM$FILE_DEV>, and then
888 the CRTL C<environ> array.
890 In all operations on %ENV, the key string is treated as if it
891 were entirely uppercase, regardless of the case actually
892 specified in the Perl expression.
894 When an element of C<%ENV> is read, the locations to which
895 F<PERL_ENV_TABLES> points are checked in order, and the value
896 obtained from the first successful lookup is returned. If the
897 name of the C<%ENV> element contains a semi-colon, it and
898 any characters after it are removed. These are ignored when
899 the CRTL C<environ> array or a CLI symbol table is consulted.
900 However, the name is looked up in a logical name table, the
901 suffix after the semi-colon is treated as the translation index
902 to be used for the lookup. This lets you look up successive values
903 for search list logical names. For instance, if you say
905 $ Define STORY once,upon,a,time,there,was
906 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
907 _$ -e "{ print $ENV{'story;'.$i},' '}"
909 Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
910 that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
911 is found, rather than a CLI symbol or CRTL C<environ> element with
914 When an element of C<%ENV> is set to a defined string, the
915 corresponding definition is made in the location to which the
916 first translation of F<PERL_ENV_TABLES> points. If this causes a
917 logical name to be created, it is defined in supervisor mode.
918 (The same is done if an existing logical name was defined in
919 executive or kernel mode; an existing user or supervisor mode
920 logical name is reset to the new value.) If the value is an empty
921 string, the logical name's translation is defined as a single NUL
922 (ASCII 00) character, since a logical name cannot translate to a
923 zero-length string. (This restriction does not apply to CLI symbols
924 or CRTL C<environ> values; they are set to the empty string.)
925 An element of the CRTL C<environ> array can be set only if your
926 copy of Perl knows about the CRTL's C<setenv()> function. (This is
927 present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
928 to see whether your copy of Perl was built with a CRTL that has this
931 When an element of C<%ENV> is set to C<undef>,
932 the element is looked up as if it were being read, and if it is
933 found, it is deleted. (An item "deleted" from the CRTL C<environ>
934 array is set to the empty string; this can only be done if your
935 copy of Perl knows about the CRTL C<setenv()> function.) Using
936 C<delete> to remove an element from C<%ENV> has a similar effect,
937 but after the element is deleted, another attempt is made to
938 look up the element, so an inner-mode logical name or a name in
939 another location will replace the logical name just deleted.
940 In either case, only the first value found searching PERL_ENV_TABLES
941 is altered. It is not possible at present to define a search list
942 logical name via %ENV.
944 The element C<$ENV{DEFAULT}> is special: when read, it returns
945 Perl's current default device and directory, and when set, it
946 resets them, regardless of the definition of F<PERL_ENV_TABLES>.
947 It cannot be cleared or deleted; attempts to do so are silently
950 Note that if you want to pass on any elements of the
951 C-local environ array to a subprocess which isn't
952 started by fork/exec, or isn't running a C program, you
953 can "promote" them to logical names in the current
954 process, which will then be inherited by all subprocesses,
957 foreach my $key (qw[C-local keys you want promoted]) {
958 my $temp = $ENV{$key}; # read from C-local array
959 $ENV{$key} = $temp; # and define as logical name
962 (You can't just say C<$ENV{$key} = $ENV{$key}>, since the
963 Perl optimizer is smart enough to elide the expression.)
965 Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
966 a fatal error. This is equivalent to doing the following from DCL:
970 You can imagine how bad things would be if, for example, the SYS$MANAGER
971 or SYS$SYSTEM logicals were deleted.
973 At present, the first time you iterate over %ENV using
974 C<keys>, or C<values>, you will incur a time penalty as all
975 logical names are read, in order to fully populate %ENV.
976 Subsequent iterations will not reread logical names, so they
977 won't be as slow, but they also won't reflect any changes
978 to logical name tables caused by other programs.
980 You do need to be careful with the logicals representing process-permanent
981 files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
982 logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
983 stripped off if you want to use it. (In previous versions of Perl it wasn't
984 possible to get the values of these logicals, as the null byte acted as an
985 end-of-string marker)
989 The string value of C<$!> is that returned by the CRTL's
990 strerror() function, so it will include the VMS message for
991 VMS-specific errors. The numeric value of C<$!> is the
992 value of C<errno>, except if errno is EVMSERR, in which
993 case C<$!> contains the value of vaxc$errno. Setting C<$!>
994 always sets errno to the value specified. If this value is
995 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
996 that the string value of C<$!> won't reflect the VMS error
997 message from before C<$!> was set.
1001 This variable provides direct access to VMS status values
1002 in vaxc$errno, which are often more specific than the
1003 generic Unix-style error messages in C<$!>. Its numeric value
1004 is the value of vaxc$errno, and its string value is the
1005 corresponding VMS message string, as retrieved by sys$getmsg().
1006 Setting C<$^E> sets vaxc$errno to the value specified.
1008 While Perl attempts to keep the vaxc$errno value to be current, if
1009 errno is not EVMSERR, it may not be from the current operation.
1013 The "status value" returned in C<$?> is synthesized from the
1014 actual exit status of the subprocess in a way that approximates
1015 POSIX wait(5) semantics, in order to allow Perl programs to
1016 portably test for successful completion of subprocesses. The
1017 low order 8 bits of C<$?> are always 0 under VMS, since the
1018 termination status of a process may or may not have been
1019 generated by an exception.
1021 The next 8 bits contain the termination status of the program.
1023 If the child process follows the convention of C programs
1024 compiled with the _POSIX_EXIT macro set, the status value will
1025 contain the actual value of 0 to 255 returned by that program
1028 With the _POSIX_EXIT macro set, the exit code of zero is represented
1029 as 1, and the values from 1 to 255 are encoded by the equation
1030 VMS_status = 0x35a000 + (exit_code * 8).
1032 For other termination statuses, the severity portion of the
1033 subprocess' exit status: if the severity was success or
1034 informational, these bits are all 0; if the severity was
1035 warning, they contain a value of 1; if the severity was
1036 error or fatal error, they contain the actual severity bits,
1037 which turns out to be a value of 2 for error and 4 for fatal error.
1039 As a result, C<$?> will always be zero if the subprocess' exit
1040 status indicated successful completion, and non-zero if a
1041 warning or error occurred or a program compliant with encoding
1042 _POSIX_EXIT values was run and set a status.
1044 How can you tell the difference? You can not unless you look at
1045 the ${^CHILD_ERROR_NATIVE} code. The ${^CHILD_ERROR_NATIVE} code
1046 returns the actual VMS status value and check the severity bits.
1047 If the severity bits are clear, then the numeric value is code
1048 passed back from the application.
1050 In practice, Perl scripts that call programs that return _POSIX_EXIT
1051 type status codes will be expecting those codes, and programs that
1052 call traditional VMS programs will be expecting the previous behavior.
1054 And success is always the code 0.
1056 Conversely, when setting C<$?> in an END block, an attempt is made
1057 to convert the POSIX value into a native status intelligible to
1058 the operating system upon exiting Perl. What this boils down to
1059 is that setting C<$?> to zero results in the generic success value
1060 SS$_NORMAL, and setting C<$?> to a non-zero value results in the
1061 generic failure status SS$_ABORT. See also L<perlport/exit>.
1063 The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
1064 VMS exit status instead of the default emulation of POSIX status
1065 described above. This pragma also disables the conversion of
1066 non-zero values to SS$_ABORT when setting C<$?> in an END
1067 block (but zero will still be converted to SS$_NORMAL).
1071 Setting C<$|> for an I/O stream causes data to be flushed
1072 all the way to disk on each write (I<i.e.> not just to
1073 the underlying RMS buffers for a file). In other words,
1074 it's equivalent to calling fflush() and fsync() from C.
1078 =head1 Standard modules with VMS-specific differences
1082 SDBM_File works properly on VMS. It has, however, one minor
1083 difference. The database directory file created has a F<.sdbm_dir>
1084 extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
1085 directory files, and using them for other purposes could cause unacceptable
1088 =head1 Revision date
1090 This document was last updated on 14-Oct-2005, for Perl 5,
1095 Charles Bailey bailey@cor.newman.upenn.edu
1096 Craig Berry craigberry@mac.com
1097 Dan Sugalski dan@sidhe.org
1098 John Malmberg wb8tyw@qsl.net