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@newman.upenn.edu.
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, you shouldn't nest the source directory
125 too deeply in your directory structure, lest you eccedd RMS'
126 maximum of 8 levels of subdirectory in a filespec. (You
127 can use rooted logical names to get another 8 levels of
128 nesting, if you can't place the files near the top of
129 the physical directory structure.)
131 VMS support for this process in the current release of Perl
132 is sufficient to handle most extensions. However, it does
133 not yet recognize extra libraries required to build shareable
134 images which are part of an extension, so these must be added
135 to the linker options file for the extension by hand. For
136 instance, if the F<PGPLOT> extension to Perl requires the
137 F<PGPLOTSHR.EXE> shareable image in order to properly link
138 the Perl extension, then the line C<PGPLOTSHR/Share> must
139 be added to the linker options file F<PGPLOT.Opt> produced
140 during the build process for the Perl extension.
142 By default, the shareable image for an extension is placed
143 F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
144 installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
145 F<VMS_AXP>, and I<Extname> is the name of the extension, with
146 each C<::> translated to C<.>). (See the MakeMaker documentation
147 for more details on installation options for extensions.)
148 However, it can be manually placed in any of several locations:
149 - the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
150 of one of the directories in C<@INC> (where I<PVers>
151 is the version of Perl you're using, as supplied in C<$]>,
152 with '.' converted to '_'), or
153 - one of the directories in C<@INC>, or
154 - a directory which the extensions Perl library module
155 passes to the DynaLoader when asking it to map
156 the shareable image, or
157 - F<Sys$Share> or F<Sys$Library>.
158 If the shareable image isn't in any of these places, you'll need
159 to define a logical name I<Extshortname>, where I<Extshortname>
160 is the portion of the extension's name after the last C<::>, which
161 translates to the full file specification of the shareable image.
163 =head1 File specifications
167 We have tried to make Perl aware of both VMS-style and Unix-
168 style file specifications wherever possible. You may use
169 either style, or both, on the command line and in scripts,
170 but you may not combine the two styles within a single fle
171 specification. VMS Perl interprets Unix pathnames in much
172 the same way as the CRTL (I<e.g.> the first component of
173 an absolute path is read as the device name for the
174 VMS file specification). There are a set of functions
175 provided in the C<VMS::Filespec> package for explicit
176 interconversion between VMS and Unix syntax; its
177 documentation provides more details.
179 Filenames are, of course, still case-insensitive. For
180 consistency, most Perl routines return filespecs using
181 lower case letters only, regardless of the case used in
182 the arguments passed to them. (This is true only when
183 running under VMS; Perl respects the case-sensitivity
186 We've tried to minimize the dependence of Perl library
187 modules on Unix syntax, but you may find that some of these,
188 as well as some scripts written for Unix systems, will
189 require that you use Unix syntax, since they will assume that
190 '/' is the directory separator, I<etc.> If you find instances
191 of this in the Perl distribution itself, please let us know,
192 so we can try to work around them.
194 =head2 Wildcard expansion
196 File specifications containing wildcards are allowed both on
197 the command line and within Perl globs (e.g. <CE<lt>*.cE<gt>>). If
198 the wildcard filespec uses VMS syntax, the resultant
199 filespecs will follow VMS syntax; if a Unix-style filespec is
200 passed in, Unix-style filespecs will be returned.
202 In both cases, VMS wildcard expansion is performed. (csh-style
203 wildcard expansion is available if you use C<File::Glob::glob>.)
204 If the wildcard filespec contains a device or directory
205 specification, then the resultant filespecs will also contain
206 a device and directory; otherwise, device and directory
207 information are removed. VMS-style resultant filespecs will
208 contain a full device and directory, while Unix-style
209 resultant filespecs will contain only as much of a directory
210 path as was present in the input filespec. For example, if
211 your default directory is Perl_Root:[000000], the expansion
212 of C<[.t]*.*> will yield filespecs like
213 "perl_root:[t]base.dir", while the expansion of C<t/*/*> will
214 yield filespecs like "t/base.dir". (This is done to match
215 the behavior of glob expansion performed by Unix shells.)
217 Similarly, the resultant filespec will contain the file version
218 only if one was present in the input filespec.
222 Input and output pipes to Perl filehandles are supported; the
223 "file name" is passed to lib$spawn() for asynchronous
224 execution. You should be careful to close any pipes you have
225 opened in a Perl script, lest you leave any "orphaned"
226 subprocesses around when Perl exits.
228 You may also use backticks to invoke a DCL subprocess, whose
229 output is used as the return value of the expression. The
230 string between the backticks is handled as if it were the
231 argument to the C<system> operator (see below). In this case,
232 Perl will wait for the subprocess to complete before continuing.
234 =head1 PERL5LIB and PERLLIB
236 The PERL5LIB and PERLLIB logical names work as documented L<perl>,
237 except that the element separator is '|' instead of ':'. The
238 directory specifications may use either VMS or Unix syntax.
242 =head2 I/O redirection and backgrounding
244 Perl for VMS supports redirection of input and output on the
245 command line, using a subset of Bourne shell syntax:
247 <F<file> reads stdin from F<file>,
248 >F<file> writes stdout to F<file>,
249 >>F<file> appends stdout to F<file>,
250 2>F<file> writes stderr to F<file>, and
251 2>>F<file> appends stderr to F<file>.
253 In addition, output may be piped to a subprocess, using the
254 character '|'. Anything after this character on the command
255 line is passed to a subprocess for execution; the subprocess
256 takes the output of Perl as its input.
258 Finally, if the command line ends with '&', the entire
259 command is run in the background as an asynchronous
262 =head2 Command line switches
264 The following command line switches behave differently under
265 VMS than described in L<perlrun>. Note also that in order
266 to pass uppercase switches to Perl, you need to enclose
267 them in double-quotes on the command line, since the CRTL
268 downcases all unquoted strings.
274 If the C<-i> switch is present but no extension for a backup
275 copy is given, then inplace editing creates a new version of
276 a file; the existing copy is not deleted. (Note that if
277 an extension is given, an existing file is renamed to the backup
278 file, as is the case under other operating systems, so it does
279 not remain as a previous version under the original filename.)
283 If the C<-S> switch is present I<and> the script name does
284 not contain a directory, then Perl translates the logical
285 name DCL$PATH as a searchlist, using each translation as
286 a directory in which to look for the script. In addition,
287 if no file type is specified, Perl looks in each directory
288 for a file matching the name specified, with a blank type,
289 a type of F<.pl>, and a type of F<.com>, in that order.
293 The C<-u> switch causes the VMS debugger to be invoked
294 after the Perl program is compiled, but before it has
295 run. It does not create a core dump file.
299 =head1 Perl functions
301 As of the time this document was last revised, the following
302 Perl functions were implemented in the VMS port of Perl
303 (functions marked with * are discussed in more detail below):
305 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
306 caller, chdir, chmod, chown, chomp, chop, chr,
307 close, closedir, cos, crypt*, defined, delete,
308 die, do, dump*, each, endpwent, eof, eval, exec*,
309 exists, exit, exp, fileno, fork*, getc, getlogin,
310 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
311 grep, hex, import, index, int, join, keys, kill*,
312 last, lc, lcfirst, length, local, localtime, log, m//,
313 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
314 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
315 qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
316 require, reset, return, reverse, rewinddir, rindex,
317 rmdir, s///, scalar, seek, seekdir, select(internal),
318 select (system call)*, setpwent, shift, sin, sleep,
319 sort, splice, split, sprintf, sqrt, srand, stat,
320 study, substr, sysread, system*, syswrite, tell,
321 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
322 undef, unlink*, unpack, untie, unshift, use, utime*,
323 values, vec, wait, waitpid*, wantarray, warn, write, y///
325 The following functions were not implemented in the VMS port,
326 and calling them produces a fatal error (usually) or
327 undefined behavior (rarely, we hope):
329 chroot, dbmclose, dbmopen, fcntl, flock,
330 getpgrp, getppid, getpriority, getgrent, getgrgid,
331 getgrnam, setgrent, endgrent, ioctl, link, lstat,
332 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
333 semget, semop, setpgrp, setpriority, shmctl, shmget,
334 shmread, shmwrite, socketpair, symlink, syscall
336 The following functions are available on Perls compiled with Dec C 5.2 or
337 greater and running VMS 7.0 or greater
341 The following functions may or may not be implemented,
342 depending on what type of socket support you've built into
345 accept, bind, connect, getpeername,
346 gethostbyname, getnetbyname, getprotobyname,
347 getservbyname, gethostbyaddr, getnetbyaddr,
348 getprotobynumber, getservbyport, gethostent,
349 getnetent, getprotoent, getservent, sethostent,
350 setnetent, setprotoent, setservent, endhostent,
351 endnetent, endprotoent, endservent, getsockname,
352 getsockopt, listen, recv, select(system call)*,
353 send, setsockopt, shutdown, socket
359 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
360 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
361 advertised. The return values for C<-r>, C<-w>, and C<-x>
362 tell you whether you can actually access the file; this may
363 not reflect the UIC-based file protections. Since real and
364 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
365 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
366 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
367 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
368 VMS, and the values returned by these tests reflect whatever
369 your CRTL C<stat()> routine does to the equivalent bits in the
370 st_mode field. Finally, C<-d> returns true if passed a device
371 specification without an explicit directory (e.g. C<DUA1:>), as
372 well as if passed a directory.
374 Note: Some sites have reported problems when using the file-access
375 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
376 Specifically, since DFS does not currently provide access to the
377 extended file header of files on remote volumes, attempts to
378 examine the ACL fail, and the file tests will return false,
379 with C<$!> indicating that the file does not exist. You can
380 use C<stat> on these files, since that checks UIC-based protection
381 only, and then manually check the appropriate bits, as defined by
382 your C compiler's F<stat.h>, in the mode value it returns, if you
383 need an approximation of the file's protections.
387 Backticks create a subprocess, and pass the enclosed string
388 to it for execution as a DCL command. Since the subprocess is
389 created directly via C<lib$spawn()>, any valid DCL command string
392 =item binmode FILEHANDLE
394 The C<binmode> operator will attempt to insure that no translation
395 of carriage control occurs on input from or output to this filehandle.
396 Since this involves reopening the file and then restoring its
397 file position indicator, if this function returns FALSE, the
398 underlying filehandle may no longer point to an open file, or may
399 point to a different position in the file than before C<binmode>
402 Note that C<binmode> is generally not necessary when using normal
403 filehandles; it is provided so that you can control I/O to existing
404 record-structured files when necessary. You can also use the
405 C<vmsfopen> function in the VMS::Stdio extension to gain finer
406 control of I/O to files and devices with different record structures.
408 =item crypt PLAINTEXT, USER
410 The C<crypt> operator uses the C<sys$hash_password> system
411 service to generate the hashed representation of PLAINTEXT.
412 If USER is a valid username, the algorithm and salt values
413 are taken from that user's UAF record. If it is not, then
414 the preferred algorithm and a salt of 0 are used. The
415 quadword encrypted value is returned as an 8-character string.
417 The value returned by C<crypt> may be compared against
418 the encrypted password from the UAF returned by the C<getpw*>
419 functions, in order to authenticate users. If you're
420 going to do this, remember that the encrypted password in
421 the UAF was generated using uppercase username and
422 password strings; you'll have to upcase the arguments to
423 C<crypt> to insure that you'll get the proper value:
425 sub validate_passwd {
426 my($user,$passwd) = @_;
428 if ( !($pwdhash = (getpwnam($user))[1]) ||
429 $pwdhash ne crypt("\U$passwd","\U$name") ) {
430 intruder_alert($name);
437 Rather than causing Perl to abort and dump core, the C<dump>
438 operator invokes the VMS debugger. If you continue to
439 execute the Perl program under the debugger, control will
440 be transferred to the label specified as the argument to
441 C<dump>, or, if no label was specified, back to the
442 beginning of the program. All other state of the program
443 (I<e.g.> values of variables, open file handles) are not
444 affected by calling C<dump>.
448 The C<exec> operator behaves in one of two different ways.
449 If called after a call to C<fork>, it will invoke the CRTL
450 C<execv()> routine, passing its arguments to the subprocess
451 created by C<fork> for execution. In this case, it is
452 subject to all limitations that affect C<execv()>. (In
453 particular, this usually means that the command executed in
454 the subprocess must be an image compiled from C source code,
455 and that your options for passing file descriptors and signal
456 handlers to the subprocess are limited.)
458 If the call to C<exec> does not follow a call to C<fork>, it
459 will cause Perl to exit, and to invoke the command given as
460 an argument to C<exec> via C<lib$do_command>. If the argument
461 begins with '@' or '$' (other than as part of a filespec), then it
462 is executed as a DCL command. Otherwise, the first token on
463 the command line is treated as the filespec of an image to
464 run, and an attempt is made to invoke it (using F<.Exe> and
465 the process defaults to expand the filespec) and pass the
466 rest of C<exec>'s argument to it as parameters.
468 You can use C<exec> in both ways within the same script, as
469 long as you call C<fork> and C<exec> in pairs. Perl
470 keeps track of how many times C<fork> and C<exec> have been
471 called, and will call the CRTL C<execv()> routine if there have
472 previously been more calls to C<fork> than to C<exec>.
476 The C<fork> operator works in the same way as the CRTL
477 C<vfork()> routine, which is quite different under VMS than
478 under Unix. Specifically, while C<fork> returns 0 after it
479 is called and the subprocess PID after C<exec> is called, in
480 both cases the thread of execution is within the parent
481 process, so there is no opportunity to perform operations in
482 the subprocess before calling C<exec>.
484 In general, the use of C<fork> and C<exec> to create
485 subprocess is not recommended under VMS; wherever possible,
486 use the C<system> operator or piped filehandles instead.
494 These operators obtain the information described in L<perlfunc>,
495 if you have the privileges necessary to retrieve the named user's
496 UAF information via C<sys$getuai>. If not, then only the C<$name>,
497 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
498 the login directory in VMS syntax, while the C<$comment> item
499 contains the login directory in Unix syntax. The C<$gcos> item
500 contains the owner field from the UAF record. The C<$quota>
505 The C<gmtime> operator will function properly if you have a
506 working CRTL C<gmtime()> routine, or if the logical name
507 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
508 which must be added to UTC to yield local time. (This logical
509 name is defined automatically if you are running a version of
510 VMS with built-in UTC support.) If neither of these cases is
511 true, a warning message is printed, and C<undef> is returned.
515 In most cases, C<kill> kill is implemented via the CRTL's C<kill()>
516 function, so it will behave according to that function's
517 documentation. If you send a SIGKILL, however, the $DELPRC system
518 service is called directly. This insures that the target
519 process is actually deleted, if at all possible. (The CRTL's C<kill()>
520 function is presently implemented via $FORCEX, which is ignored by
521 supervisor-mode images like DCL.)
523 Also, negative signal values don't do anything special under
524 VMS; they're just converted to the corresponding positive value.
528 See the entry on C<backticks> above.
530 =item select (system call)
532 If Perl was not built with socket support, the system call
533 version of C<select> is not available at all. If socket
534 support is present, then the system call version of
535 C<select> functions only for file descriptors attached
536 to sockets. It will not provide information about regular
537 files or pipes, since the CRTL C<select()> routine does not
538 provide this functionality.
542 Since VMS keeps track of files according to a different scheme
543 than Unix, it's not really possible to represent the file's ID
544 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
545 tries its best, though, and the values it uses are pretty unlikely
546 to be the same for two different files. We can't guarantee this,
547 though, so caveat scriptor.
551 The C<system> operator creates a subprocess, and passes its
552 arguments to the subprocess for execution as a DCL command.
553 Since the subprocess is created directly via C<lib$spawn()>, any
554 valid DCL command string may be specified. If the string begins with
555 '@', it is treated as a DCL command unconditionally. Otherwise, if
556 the first token contains a character used as a delimiter in file
557 specification (e.g. C<:> or C<]>), an attempt is made to expand it
558 using a default type of F<.Exe> and the process defaults, and if
559 successful, the resulting file is invoked via C<MCR>. This allows you
560 to invoke an image directly simply by passing the file specification
561 to C<system>, a common Unixish idiom. If LIST consists
562 of the empty string, C<system> spawns an interactive DCL subprocess,
563 in the same fashion as typiing B<SPAWN> at the DCL prompt.
564 Perl waits for the subprocess to complete before continuing
565 execution in the current process. As described in L<perlfunc>,
566 the return value of C<system> is a fake "status" which follows
567 POSIX semantics; see the description of C<$?> in this document
568 for more detail. The actual VMS exit status of the subprocess
569 is available in C<$^S> (as long as you haven't used another Perl
570 function that resets C<$?> and C<$^S> in the meantime).
574 The value returned by C<time> is the offset in seconds from
575 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
576 to make life easier for code coming in from the POSIX/Unix world.
580 The array returned by the C<times> operator is divided up
581 according to the same rules the CRTL C<times()> routine.
582 Therefore, the "system time" elements will always be 0, since
583 there is no difference between "user time" and "system" time
584 under VMS, and the time accumulated by subprocess may or may
585 not appear separately in the "child time" field, depending on
586 whether L<times> keeps track of subprocesses separately. Note
587 especially that the VAXCRTL (at least) keeps track only of
588 subprocesses spawned using L<fork> and L<exec>; it will not
589 accumulate the times of suprocesses spawned via pipes, L<system>,
594 C<unlink> will delete the highest version of a file only; in
595 order to delete all versions, you need to say
596 1 while (unlink LIST);
597 You may need to make this change to scripts written for a
598 Unix system which expect that after a call to C<unlink>,
599 no files with the names passed to C<unlink> will exist.
600 (Note: This can be changed at compile time; if you
601 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
602 C<define>, then C<unlink> will delete all versions of a
603 file on the first call.)
605 C<unlink> will delete a file if at all possible, even if it
606 requires changing file protection (though it won't try to
607 change the protection of the parent directory). You can tell
608 whether you've got explicit delete access to a file by using the
609 C<VMS::Filespec::candelete> operator. For instance, in order
610 to delete only files to which you have delete access, you could
616 next unless VMS::Filespec::candelete($file);
617 $num += unlink $file;
622 (or you could just use C<VMS::Stdio::remove>, if you've installed
623 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
624 change the file protection to delete the file, and you interrupt it
625 in midstream, the file may be left intact, but with a changed ACL
626 allowing you delete access.
630 Since ODS-2, the VMS file structure for disk files, does not keep
631 track of access times, this operator changes only the modification
632 time of the file (VMS revision date).
634 =item waitpid PID,FLAGS
636 If PID is a subprocess started by a piped L<open>, C<waitpid>
637 will wait for that subprocess, and return its final
638 status value. If PID is a subprocess created in some other way
639 (e.g. SPAWNed before Perl was invoked), or is not a subprocess of
640 the current process, C<waitpid> will check once per second whether
641 the process has completed, and when it has, will return 0. (If PID
642 specifies a process that isn't a subprocess of the current process,
643 and you invoked Perl with the C<-w> switch, a warning will be issued.)
645 The FLAGS argument is ignored in all cases.
649 =head1 Perl variables
651 The following VMS-specific information applies to the indicated
652 "special" Perl variables, in addition to the general information
653 in L<perlvar>. Where there is a conflict, this infrmation
660 The operation of the C<%ENV> array depends on the translation
661 of the logical name F<PERL_ENV_TABLES>. If defined, it should
662 be a search list, each element of which specifies a location
663 for C<%ENV> elements. If you tell Perl to read or set the
664 element C<$ENV{>I<name>C<}>, then Perl uses the translations of
665 F<PERL_ENV_TABLES> as follows:
671 This string tells Perl to consult the CRTL's internal C<environ>
672 array of key-value pairs, using I<name> as the key. In most cases,
673 this contains only a few keys, but if Perl was invoked via the C
674 C<exec[lv]e()> function, as is the case for CGI processing by some
675 HTTP servers, then the C<environ> array may have been populated by
680 A string beginning with C<CLISYM_>tells Perl to consult the CLI's
681 symbol tables, using I<name> as the name of the symbol. When reading
682 an element of C<%ENV>, the local symbol table is scanned first, followed
683 by the global symbol table.. The characters following C<CLISYM_> are
684 significant when an element of C<%ENV> is set or deleted: if the
685 complete string is C<CLISYM_LOCAL>, the change is made in the local
686 symbol table, otherwise the global symbol table is changed.
688 =item Any other string
690 If an element of F<PERL_ENV_TABLES> translates to any other string,
691 that string is used as the name of a logical name table, which is
692 consulted using I<name> as the logical name. The normal search
693 order of access modes is used.
697 F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
698 you make while Perl is running do not affect the behavior of C<%ENV>.
699 If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
700 first the logical name tables specified by F<LNM$FILE_DEV>, and then
701 the CRTL C<environ> array.
703 In all operations on %ENV, the key string is treated as if it
704 were entirely uppercase, regardless of the case actually
705 specified in the Perl expression.
707 When an element of C<%ENV> is read, the locations to which
708 F<PERL_ENV_TABLES> points are checked in order, and the value
709 obtained from the first successful lookup is returned. If the
710 name of the C<%ENV> element contains a semi-colon, it and
711 any characters after it are removed. These are ignored when
712 the CRTL C<environ> array or a CLI symbol table is consulted.
713 However, the name is looked up in a logical name table, the
714 suffix after the semi-colon is treated as the translation index
715 to be used for the lookup. This lets you look up successive values
716 for search list logical names. For instance, if you say
718 $ Define STORY once,upon,a,time,there,was
719 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
720 _$ -e "{ print $ENV{'story;'.$i},' '}"
722 Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
723 that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
724 is found, rather than a CLI symbol or CRTL C<environ> element with
727 When an element of C<%ENV> is set to a defined string, the
728 corresponding definition is made in the location to which the
729 first translation of F<PERL_ENV_TABLES> points. If this causes a
730 logical name to be created, it is defined in supervisor mode.
731 (The same is done if an existing logical name was defined in
732 executive or kernel mode; an existing user or supervisor mode
733 logical name is reset to the new value.) If the value is an empty
734 string, the logical name's translation is defined as a single NUL
735 (ASCII 00) character, since a logical name cannot translate to a
736 zero-length string. (This restriction does not apply to CLI symbols
737 or CRTL C<environ> values; they are set to the empty string.)
738 An element of the CRTL C<environ> array can be set only if your
739 copy of Perl knows about the CRTL's C<setenv()> function. (This is
740 present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
741 to see whether your copy of Perl was built with a CRTL that has this
744 When an element of C<%ENV> is set to C<undef>,
745 the element is looked up as if it were being read, and if it is
746 found, it is deleted. (An item "deleted" from the CRTL C<environ>
747 array is set to the empty string; this can only be done if your
748 copy of Perl knows about the CRTL C<setenv()> function.) Using
749 C<delete> to remove an element from C<%ENV> has a similar effect,
750 but after the element is deleted, another attempt is made to
751 look up the element, so an inner-mode logical name or a name in
752 another location will replace the logical name just deleted.
753 In either case, only the first value found searching PERL_ENV_TABLES
754 is altered. It is not possible at present to define a search list
755 logical name via %ENV.
757 The element C<$ENV{DEFAULT}> is special: when read, it returns
758 Perl's current default device and directory, and when set, it
759 resets them, regardless of the definition of F<PERL_ENV_TABLES>.
760 It cannot be cleared or deleted; attempts to do so are silently
763 Note that if you want to pass on any elements of the
764 C-local environ array to a subprocess which isn't
765 started by fork/exec, or isn't running a C program, you
766 can "promote" them to logical names in the current
767 process, which will then be inherited by all subprocesses,
770 foreach my $key (qw[C-local keys you want promoted]) {
771 my $temp = $ENV{$key}; # read from C-local array
772 $ENV{$key} = $temp; # and define as logical name
775 (You can't just say C<$ENV{$key} = $ENV{$key}>, since the
776 Perl optimizer is smart enough to elide the expression.)
778 At present, the first time you iterate over %ENV using
779 C<keys>, or C<values>, you will incur a time penalty as all
780 logical names are read, in order to fully populate %ENV.
781 Subsequent iterations will not reread logical names, so they
782 won't be as slow, but they also won't reflect any changes
783 to logical name tables caused by other programs.
785 You do need to be careful with the logicals representing process-permanent
786 files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
787 logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
788 stripped off if you want to use it. (In previous versions of perl it wasn't
789 possible to get the values of these logicals, as the null byte acted as an
790 end-of-string marker)
794 The string value of C<$!> is that returned by the CRTL's
795 strerror() function, so it will include the VMS message for
796 VMS-specific errors. The numeric value of C<$!> is the
797 value of C<errno>, except if errno is EVMSERR, in which
798 case C<$!> contains the value of vaxc$errno. Setting C<$!>
799 always sets errno to the value specified. If this value is
800 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
801 that the string value of C<$!> won't reflect the VMS error
802 message from before C<$!> was set.
806 This variable provides direct access to VMS status values
807 in vaxc$errno, which are often more specific than the
808 generic Unix-style error messages in C<$!>. Its numeric value
809 is the value of vaxc$errno, and its string value is the
810 corresponding VMS message string, as retrieved by sys$getmsg().
811 Setting C<$^E> sets vaxc$errno to the value specified.
815 The "status value" returned in C<$?> is synthesized from the
816 actual exit status of the subprocess in a way that approximates
817 POSIX wait(5) semantics, in order to allow Perl programs to
818 portably test for successful completion of subprocesses. The
819 low order 8 bits of C<$?> are always 0 under VMS, since the
820 termination status of a process may or may not have been
821 generated by an exception. The next 8 bits are derived from
822 severity portion of the subprocess' exit status: if the
823 severity was success or informational, these bits are all 0;
824 otherwise, they contain the severity value shifted left one bit.
825 As a result, C<$?> will always be zero if the subprocess' exit
826 status indicated successful completion, and non-zero if a
827 warning or error occurred. The actual VMS exit status may
828 be found in C<$^S> (q.v.).
832 Under VMS, this is the 32-bit VMS status value returned by the
833 last subprocess to complete. Unlink C<$?>, no manipulation
834 is done to make this look like a POSIX wait(5) value, so it
835 may be treated as a normal VMS status value.
839 Setting C<$|> for an I/O stream causes data to be flushed
840 all the way to disk on each write (I<i.e.> not just to
841 the underlying RMS buffers for a file). In other words,
842 it's equivalent to calling fflush() and fsync() from C.
846 =head1 Standard modules with VMS-specific differences
850 SDBM_File works peroperly on VMS. It has, however, one minor
851 difference. The database directory file created has a L<.sdbm_dir>
852 extension rather than a L<.dir> extension. L<.dir> files are VMS filesystem
853 directory files, and using them for other purposes could cause unacceptable
858 This document was last updated on 26-Feb-2000, for Perl 5,
863 Charles Bailey <bailey@cor.newman.upenn.edu>
864 Dan Sugalski <dan@sidhe.org>