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, you shouldn't nest the source directory
125 too deeply in your directory structure, lest you exceed 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 file
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 in 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, 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
337 5.2 or greater and running VMS 7.0 or greater:
341 The following functions are available on Perls built on VMS 7.2 or
344 fcntl (without locking)
346 The following functions may or may not be implemented,
347 depending on what type of socket support you've built into
350 accept, bind, connect, getpeername,
351 gethostbyname, getnetbyname, getprotobyname,
352 getservbyname, gethostbyaddr, getnetbyaddr,
353 getprotobynumber, getservbyport, gethostent,
354 getnetent, getprotoent, getservent, sethostent,
355 setnetent, setprotoent, setservent, endhostent,
356 endnetent, endprotoent, endservent, getsockname,
357 getsockopt, listen, recv, select(system call)*,
358 send, setsockopt, shutdown, socket
364 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
365 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
366 advertised. The return values for C<-r>, C<-w>, and C<-x>
367 tell you whether you can actually access the file; this may
368 not reflect the UIC-based file protections. Since real and
369 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
370 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
371 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
372 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
373 VMS, and the values returned by these tests reflect whatever
374 your CRTL C<stat()> routine does to the equivalent bits in the
375 st_mode field. Finally, C<-d> returns true if passed a device
376 specification without an explicit directory (e.g. C<DUA1:>), as
377 well as if passed a directory.
379 Note: Some sites have reported problems when using the file-access
380 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
381 Specifically, since DFS does not currently provide access to the
382 extended file header of files on remote volumes, attempts to
383 examine the ACL fail, and the file tests will return false,
384 with C<$!> indicating that the file does not exist. You can
385 use C<stat> on these files, since that checks UIC-based protection
386 only, and then manually check the appropriate bits, as defined by
387 your C compiler's F<stat.h>, in the mode value it returns, if you
388 need an approximation of the file's protections.
392 Backticks create a subprocess, and pass the enclosed string
393 to it for execution as a DCL command. Since the subprocess is
394 created directly via C<lib$spawn()>, any valid DCL command string
397 =item binmode FILEHANDLE
399 The C<binmode> operator will attempt to insure that no translation
400 of carriage control occurs on input from or output to this filehandle.
401 Since this involves reopening the file and then restoring its
402 file position indicator, if this function returns FALSE, the
403 underlying filehandle may no longer point to an open file, or may
404 point to a different position in the file than before C<binmode>
407 Note that C<binmode> is generally not necessary when using normal
408 filehandles; it is provided so that you can control I/O to existing
409 record-structured files when necessary. You can also use the
410 C<vmsfopen> function in the VMS::Stdio extension to gain finer
411 control of I/O to files and devices with different record structures.
413 =item crypt PLAINTEXT, USER
415 The C<crypt> operator uses the C<sys$hash_password> system
416 service to generate the hashed representation of PLAINTEXT.
417 If USER is a valid username, the algorithm and salt values
418 are taken from that user's UAF record. If it is not, then
419 the preferred algorithm and a salt of 0 are used. The
420 quadword encrypted value is returned as an 8-character string.
422 The value returned by C<crypt> may be compared against
423 the encrypted password from the UAF returned by the C<getpw*>
424 functions, in order to authenticate users. If you're
425 going to do this, remember that the encrypted password in
426 the UAF was generated using uppercase username and
427 password strings; you'll have to upcase the arguments to
428 C<crypt> to insure that you'll get the proper value:
430 sub validate_passwd {
431 my($user,$passwd) = @_;
433 if ( !($pwdhash = (getpwnam($user))[1]) ||
434 $pwdhash ne crypt("\U$passwd","\U$name") ) {
435 intruder_alert($name);
442 Rather than causing Perl to abort and dump core, the C<dump>
443 operator invokes the VMS debugger. If you continue to
444 execute the Perl program under the debugger, control will
445 be transferred to the label specified as the argument to
446 C<dump>, or, if no label was specified, back to the
447 beginning of the program. All other state of the program
448 (I<e.g.> values of variables, open file handles) are not
449 affected by calling C<dump>.
453 The C<exec> operator behaves in one of two different ways.
454 If called after a call to C<fork>, it will invoke the CRTL
455 C<execv()> routine, passing its arguments to the subprocess
456 created by C<fork> for execution. In this case, it is
457 subject to all limitations that affect C<execv()>. (In
458 particular, this usually means that the command executed in
459 the subprocess must be an image compiled from C source code,
460 and that your options for passing file descriptors and signal
461 handlers to the subprocess are limited.)
463 If the call to C<exec> does not follow a call to C<fork>, it
464 will cause Perl to exit, and to invoke the command given as
465 an argument to C<exec> via C<lib$do_command>. If the argument
466 begins with '@' or '$' (other than as part of a filespec), then it
467 is executed as a DCL command. Otherwise, the first token on
468 the command line is treated as the filespec of an image to
469 run, and an attempt is made to invoke it (using F<.Exe> and
470 the process defaults to expand the filespec) and pass the
471 rest of C<exec>'s argument to it as parameters. If the token
472 has no file type, and matches a file with null type, then an
473 attempt is made to determine whether the file is an executable
474 image which should be invoked using C<MCR> or a text file which
475 should be passed to DCL as a command procedure.
477 You can use C<exec> in both ways within the same script, as
478 long as you call C<fork> and C<exec> in pairs. Perl
479 keeps track of how many times C<fork> and C<exec> have been
480 called, and will call the CRTL C<execv()> routine if there have
481 previously been more calls to C<fork> than to C<exec>.
485 The C<fork> operator works in the same way as the CRTL
486 C<vfork()> routine, which is quite different under VMS than
487 under Unix. Specifically, while C<fork> returns 0 after it
488 is called and the subprocess PID after C<exec> is called, in
489 both cases the thread of execution is within the parent
490 process, so there is no opportunity to perform operations in
491 the subprocess before calling C<exec>.
493 In general, the use of C<fork> and C<exec> to create
494 subprocesses is not recommended under VMS; wherever possible,
495 use the C<system> operator or piped filehandles instead.
503 These operators obtain the information described in L<perlfunc>,
504 if you have the privileges necessary to retrieve the named user's
505 UAF information via C<sys$getuai>. If not, then only the C<$name>,
506 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
507 the login directory in VMS syntax, while the C<$comment> item
508 contains the login directory in Unix syntax. The C<$gcos> item
509 contains the owner field from the UAF record. The C<$quota>
514 The C<gmtime> operator will function properly if you have a
515 working CRTL C<gmtime()> routine, or if the logical name
516 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
517 which must be added to UTC to yield local time. (This logical
518 name is defined automatically if you are running a version of
519 VMS with built-in UTC support.) If neither of these cases is
520 true, a warning message is printed, and C<undef> is returned.
524 In most cases, C<kill> is implemented via the CRTL's C<kill()>
525 function, so it will behave according to that function's
526 documentation. If you send a SIGKILL, however, the $DELPRC system
527 service is called directly. This insures that the target
528 process is actually deleted, if at all possible. (The CRTL's C<kill()>
529 function is presently implemented via $FORCEX, which is ignored by
530 supervisor-mode images like DCL.)
532 Also, negative signal values don't do anything special under
533 VMS; they're just converted to the corresponding positive value.
537 See the entry on C<backticks> above.
539 =item select (system call)
541 If Perl was not built with socket support, the system call
542 version of C<select> is not available at all. If socket
543 support is present, then the system call version of
544 C<select> functions only for file descriptors attached
545 to sockets. It will not provide information about regular
546 files or pipes, since the CRTL C<select()> routine does not
547 provide this functionality.
551 Since VMS keeps track of files according to a different scheme
552 than Unix, it's not really possible to represent the file's ID
553 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
554 tries its best, though, and the values it uses are pretty unlikely
555 to be the same for two different files. We can't guarantee this,
556 though, so caveat scriptor.
560 The C<system> operator creates a subprocess, and passes its
561 arguments to the subprocess for execution as a DCL command.
562 Since the subprocess is created directly via C<lib$spawn()>, any
563 valid DCL command string may be specified. If the string begins with
564 '@', it is treated as a DCL command unconditionally. Otherwise, if
565 the first token contains a character used as a delimiter in file
566 specification (e.g. C<:> or C<]>), an attempt is made to expand it
567 using a default type of F<.Exe> and the process defaults, and if
568 successful, the resulting file is invoked via C<MCR>. This allows you
569 to invoke an image directly simply by passing the file specification
570 to C<system>, a common Unixish idiom. If the token has no file type,
571 and matches a file with null type, then an attempt is made to
572 determine whether the file is an executable image which should be
573 invoked using C<MCR> or a text file which should be passed to DCL
574 as a command procedure.
576 If LIST consists of the empty string, C<system> spawns an
577 interactive DCL subprocess, in the same fashion as typing
578 B<SPAWN> at the DCL prompt.
580 Perl waits for the subprocess to complete before continuing
581 execution in the current process. As described in L<perlfunc>,
582 the return value of C<system> is a fake "status" which follows
583 POSIX semantics unless the pragma C<use vmsish 'status'> is in
584 effect; see the description of C<$?> in this document for more
589 The value returned by C<time> is the offset in seconds from
590 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
591 to make life easier for code coming in from the POSIX/Unix world.
595 The array returned by the C<times> operator is divided up
596 according to the same rules the CRTL C<times()> routine.
597 Therefore, the "system time" elements will always be 0, since
598 there is no difference between "user time" and "system" time
599 under VMS, and the time accumulated by a subprocess may or may
600 not appear separately in the "child time" field, depending on
601 whether L<times> keeps track of subprocesses separately. Note
602 especially that the VAXCRTL (at least) keeps track only of
603 subprocesses spawned using L<fork> and L<exec>; it will not
604 accumulate the times of subprocesses spawned via pipes, L<system>,
609 C<unlink> will delete the highest version of a file only; in
610 order to delete all versions, you need to say
614 You may need to make this change to scripts written for a
615 Unix system which expect that after a call to C<unlink>,
616 no files with the names passed to C<unlink> will exist.
617 (Note: This can be changed at compile time; if you
618 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
619 C<define>, then C<unlink> will delete all versions of a
620 file on the first call.)
622 C<unlink> will delete a file if at all possible, even if it
623 requires changing file protection (though it won't try to
624 change the protection of the parent directory). You can tell
625 whether you've got explicit delete access to a file by using the
626 C<VMS::Filespec::candelete> operator. For instance, in order
627 to delete only files to which you have delete access, you could
633 next unless VMS::Filespec::candelete($file);
634 $num += unlink $file;
639 (or you could just use C<VMS::Stdio::remove>, if you've installed
640 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
641 change the file protection to delete the file, and you interrupt it
642 in midstream, the file may be left intact, but with a changed ACL
643 allowing you delete access.
647 Since ODS-2, the VMS file structure for disk files, does not keep
648 track of access times, this operator changes only the modification
649 time of the file (VMS revision date).
651 =item waitpid PID,FLAGS
653 If PID is a subprocess started by a piped C<open()> (see L<open>),
654 C<waitpid> will wait for that subprocess, and return its final
655 status value in C<$?>. If PID is a subprocess created in some other
656 way (e.g. SPAWNed before Perl was invoked), or is not a subprocess
657 of the current process, C<waitpid> will attempt to read from the
658 process's termination mailbox, making the final status available in
659 C<$?> when the process completes. If the process specified by PID
660 has no termination mailbox, C<waitpid> will simply check once per
661 second whether the process has completed, and return when it has.
662 (If PID specifies a process that isn't a subprocess of the current
663 process, and you invoked Perl with the C<-w> switch, a warning will
666 Returns PID on success, -1 on error. The FLAGS argument is ignored
671 =head1 Perl variables
673 The following VMS-specific information applies to the indicated
674 "special" Perl variables, in addition to the general information
675 in L<perlvar>. Where there is a conflict, this information
682 The operation of the C<%ENV> array depends on the translation
683 of the logical name F<PERL_ENV_TABLES>. If defined, it should
684 be a search list, each element of which specifies a location
685 for C<%ENV> elements. If you tell Perl to read or set the
686 element C<$ENV{>I<name>C<}>, then Perl uses the translations of
687 F<PERL_ENV_TABLES> as follows:
693 This string tells Perl to consult the CRTL's internal C<environ>
694 array of key-value pairs, using I<name> as the key. In most cases,
695 this contains only a few keys, but if Perl was invoked via the C
696 C<exec[lv]e()> function, as is the case for CGI processing by some
697 HTTP servers, then the C<environ> array may have been populated by
702 A string beginning with C<CLISYM_>tells Perl to consult the CLI's
703 symbol tables, using I<name> as the name of the symbol. When reading
704 an element of C<%ENV>, the local symbol table is scanned first, followed
705 by the global symbol table.. The characters following C<CLISYM_> are
706 significant when an element of C<%ENV> is set or deleted: if the
707 complete string is C<CLISYM_LOCAL>, the change is made in the local
708 symbol table; otherwise the global symbol table is changed.
710 =item Any other string
712 If an element of F<PERL_ENV_TABLES> translates to any other string,
713 that string is used as the name of a logical name table, which is
714 consulted using I<name> as the logical name. The normal search
715 order of access modes is used.
719 F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
720 you make while Perl is running do not affect the behavior of C<%ENV>.
721 If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
722 first the logical name tables specified by F<LNM$FILE_DEV>, and then
723 the CRTL C<environ> array.
725 In all operations on %ENV, the key string is treated as if it
726 were entirely uppercase, regardless of the case actually
727 specified in the Perl expression.
729 When an element of C<%ENV> is read, the locations to which
730 F<PERL_ENV_TABLES> points are checked in order, and the value
731 obtained from the first successful lookup is returned. If the
732 name of the C<%ENV> element contains a semi-colon, it and
733 any characters after it are removed. These are ignored when
734 the CRTL C<environ> array or a CLI symbol table is consulted.
735 However, the name is looked up in a logical name table, the
736 suffix after the semi-colon is treated as the translation index
737 to be used for the lookup. This lets you look up successive values
738 for search list logical names. For instance, if you say
740 $ Define STORY once,upon,a,time,there,was
741 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
742 _$ -e "{ print $ENV{'story;'.$i},' '}"
744 Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
745 that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
746 is found, rather than a CLI symbol or CRTL C<environ> element with
749 When an element of C<%ENV> is set to a defined string, the
750 corresponding definition is made in the location to which the
751 first translation of F<PERL_ENV_TABLES> points. If this causes a
752 logical name to be created, it is defined in supervisor mode.
753 (The same is done if an existing logical name was defined in
754 executive or kernel mode; an existing user or supervisor mode
755 logical name is reset to the new value.) If the value is an empty
756 string, the logical name's translation is defined as a single NUL
757 (ASCII 00) character, since a logical name cannot translate to a
758 zero-length string. (This restriction does not apply to CLI symbols
759 or CRTL C<environ> values; they are set to the empty string.)
760 An element of the CRTL C<environ> array can be set only if your
761 copy of Perl knows about the CRTL's C<setenv()> function. (This is
762 present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
763 to see whether your copy of Perl was built with a CRTL that has this
766 When an element of C<%ENV> is set to C<undef>,
767 the element is looked up as if it were being read, and if it is
768 found, it is deleted. (An item "deleted" from the CRTL C<environ>
769 array is set to the empty string; this can only be done if your
770 copy of Perl knows about the CRTL C<setenv()> function.) Using
771 C<delete> to remove an element from C<%ENV> has a similar effect,
772 but after the element is deleted, another attempt is made to
773 look up the element, so an inner-mode logical name or a name in
774 another location will replace the logical name just deleted.
775 In either case, only the first value found searching PERL_ENV_TABLES
776 is altered. It is not possible at present to define a search list
777 logical name via %ENV.
779 The element C<$ENV{DEFAULT}> is special: when read, it returns
780 Perl's current default device and directory, and when set, it
781 resets them, regardless of the definition of F<PERL_ENV_TABLES>.
782 It cannot be cleared or deleted; attempts to do so are silently
785 Note that if you want to pass on any elements of the
786 C-local environ array to a subprocess which isn't
787 started by fork/exec, or isn't running a C program, you
788 can "promote" them to logical names in the current
789 process, which will then be inherited by all subprocesses,
792 foreach my $key (qw[C-local keys you want promoted]) {
793 my $temp = $ENV{$key}; # read from C-local array
794 $ENV{$key} = $temp; # and define as logical name
797 (You can't just say C<$ENV{$key} = $ENV{$key}>, since the
798 Perl optimizer is smart enough to elide the expression.)
800 Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
801 a fatal error. This is equivalent to doing the following from DCL:
805 You can imagine how bad things would be if, for example, the SYS$MANAGER
806 or SYS$SYSTEM logicals were deleted.
808 At present, the first time you iterate over %ENV using
809 C<keys>, or C<values>, you will incur a time penalty as all
810 logical names are read, in order to fully populate %ENV.
811 Subsequent iterations will not reread logical names, so they
812 won't be as slow, but they also won't reflect any changes
813 to logical name tables caused by other programs.
815 You do need to be careful with the logicals representing process-permanent
816 files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
817 logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
818 stripped off if you want to use it. (In previous versions of Perl it wasn't
819 possible to get the values of these logicals, as the null byte acted as an
820 end-of-string marker)
824 The string value of C<$!> is that returned by the CRTL's
825 strerror() function, so it will include the VMS message for
826 VMS-specific errors. The numeric value of C<$!> is the
827 value of C<errno>, except if errno is EVMSERR, in which
828 case C<$!> contains the value of vaxc$errno. Setting C<$!>
829 always sets errno to the value specified. If this value is
830 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
831 that the string value of C<$!> won't reflect the VMS error
832 message from before C<$!> was set.
836 This variable provides direct access to VMS status values
837 in vaxc$errno, which are often more specific than the
838 generic Unix-style error messages in C<$!>. Its numeric value
839 is the value of vaxc$errno, and its string value is the
840 corresponding VMS message string, as retrieved by sys$getmsg().
841 Setting C<$^E> sets vaxc$errno to the value specified.
845 The "status value" returned in C<$?> is synthesized from the
846 actual exit status of the subprocess in a way that approximates
847 POSIX wait(5) semantics, in order to allow Perl programs to
848 portably test for successful completion of subprocesses. The
849 low order 8 bits of C<$?> are always 0 under VMS, since the
850 termination status of a process may or may not have been
851 generated by an exception. The next 8 bits are derived from
852 the severity portion of the subprocess' exit status: if the
853 severity was success or informational, these bits are all 0;
854 if the severity was warning, they contain a value of 1; if the
855 severity was error or fatal error, they contain the actual
856 severity bits, which turns out to be a value of 2 for error
857 and 4 for fatal error.
859 As a result, C<$?> will always be zero if the subprocess' exit
860 status indicated successful completion, and non-zero if a
861 warning or error occurred. Conversely, when setting C<$?> in
862 an END block, an attempt is made to convert the POSIX value
863 into a native status intelligible to the operating system upon
864 exiting Perl. What this boils down to is that setting C<$?>
865 to zero results in the generic success value SS$_NORMAL, and
866 setting C<$?> to a non-zero value results in the generic
867 failure status SS$_ABORT. See also L<perlport/exit>.
869 The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
870 VMS exit status instead of the default emulation of POSIX status
871 described above. This pragma also disables the conversion of
872 non-zero values to SS$_ABORT when setting C<$?> in an END
873 block (but zero will still be converted to SS$_NORMAL).
877 Setting C<$|> for an I/O stream causes data to be flushed
878 all the way to disk on each write (I<i.e.> not just to
879 the underlying RMS buffers for a file). In other words,
880 it's equivalent to calling fflush() and fsync() from C.
884 =head1 Standard modules with VMS-specific differences
888 SDBM_File works properly on VMS. It has, however, one minor
889 difference. The database directory file created has a F<.sdbm_dir>
890 extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
891 directory files, and using them for other purposes could cause unacceptable
896 This document was last updated on 2-Oct-2001, for Perl 5,
901 Charles Bailey <bailey@cor.newman.upenn.edu>
902 Craig Berry <craigberry@mac.com>
903 Dan Sugalski <dan@sidhe.org>