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 runnning 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 Filenames are, of course, still case-insensitive. For
198 consistency, most Perl routines return filespecs using
199 lower case letters only, regardless of the case used in
200 the arguments passed to them. (This is true only when
201 running under VMS; Perl respects the case-sensitivity
204 We've tried to minimize the dependence of Perl library
205 modules on Unix syntax, but you may find that some of these,
206 as well as some scripts written for Unix systems, will
207 require that you use Unix syntax, since they will assume that
208 '/' is the directory separator, I<etc.> If you find instances
209 of this in the Perl distribution itself, please let us know,
210 so we can try to work around them.
212 =head2 Wildcard expansion
214 File specifications containing wildcards are allowed both on
215 the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>). If
216 the wildcard filespec uses VMS syntax, the resultant
217 filespecs will follow VMS syntax; if a Unix-style filespec is
218 passed in, Unix-style filespecs will be returned.
219 Similar to the behavior of wildcard globbing for a Unix shell,
220 one can escape command line wildcards with double quotation
221 marks C<"> around a perl program command line argument. However,
222 owing to the stripping of C<"> characters carried out by the C
223 handling of argv you will need to escape a construct such as
224 this one (in a directory containing the files F<PERL.C>, F<PERL.EXE>,
225 F<PERL.H>, and F<PERL.OBJ>):
227 $ perl -e "print join(' ',@ARGV)" perl.*
228 perl.c perl.exe perl.h perl.obj
230 in the following triple quoted manner:
232 $ perl -e "print join(' ',@ARGV)" """perl.*"""
235 In both the case of unquoted command line arguments or in calls
236 to C<glob()> VMS wildcard expansion is performed. (csh-style
237 wildcard expansion is available if you use C<File::Glob::glob>.)
238 If the wildcard filespec contains a device or directory
239 specification, then the resultant filespecs will also contain
240 a device and directory; otherwise, device and directory
241 information are removed. VMS-style resultant filespecs will
242 contain a full device and directory, while Unix-style
243 resultant filespecs will contain only as much of a directory
244 path as was present in the input filespec. For example, if
245 your default directory is Perl_Root:[000000], the expansion
246 of C<[.t]*.*> will yield filespecs like
247 "perl_root:[t]base.dir", while the expansion of C<t/*/*> will
248 yield filespecs like "t/base.dir". (This is done to match
249 the behavior of glob expansion performed by Unix shells.)
251 Similarly, the resultant filespec will contain the file version
252 only if one was present in the input filespec.
256 Input and output pipes to Perl filehandles are supported; the
257 "file name" is passed to lib$spawn() for asynchronous
258 execution. You should be careful to close any pipes you have
259 opened in a Perl script, lest you leave any "orphaned"
260 subprocesses around when Perl exits.
262 You may also use backticks to invoke a DCL subprocess, whose
263 output is used as the return value of the expression. The
264 string between the backticks is handled as if it were the
265 argument to the C<system> operator (see below). In this case,
266 Perl will wait for the subprocess to complete before continuing.
268 The mailbox (MBX) that perl can create to communicate with a pipe
269 defaults to a buffer size of 512. The default buffer size is
270 adjustable via the logical name PERL_MBX_SIZE provided that the
271 value falls between 128 and the SYSGEN parameter MAXBUF inclusive.
272 For example, to double the MBX size from the default within
273 a Perl program, use C<$ENV{'PERL_MBX_SIZE'} = 1024;> and then
274 open and use pipe constructs. An alternative would be to issue
277 $ Define PERL_MBX_SIZE 1024
279 before running your wide record pipe program. A larger value may
280 improve performance at the expense of the BYTLM UAF quota.
282 =head1 PERL5LIB and PERLLIB
284 The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
285 except that the element separator is '|' instead of ':'. The
286 directory specifications may use either VMS or Unix syntax.
290 =head2 I/O redirection and backgrounding
292 Perl for VMS supports redirection of input and output on the
293 command line, using a subset of Bourne shell syntax:
299 C<E<lt>file> reads stdin from C<file>,
303 C<E<gt>file> writes stdout to C<file>,
307 C<E<gt>E<gt>file> appends stdout to C<file>,
311 C<2E<gt>file> writes stderr to C<file>,
315 C<2E<gt>E<gt>file> appends stderr to C<file>, and
319 C<< 2>&1 >> redirects stderr to stdout.
323 In addition, output may be piped to a subprocess, using the
324 character '|'. Anything after this character on the command
325 line is passed to a subprocess for execution; the subprocess
326 takes the output of Perl as its input.
328 Finally, if the command line ends with '&', the entire
329 command is run in the background as an asynchronous
332 =head2 Command line switches
334 The following command line switches behave differently under
335 VMS than described in L<perlrun>. Note also that in order
336 to pass uppercase switches to Perl, you need to enclose
337 them in double-quotes on the command line, since the CRTL
338 downcases all unquoted strings.
344 If the C<-i> switch is present but no extension for a backup
345 copy is given, then inplace editing creates a new version of
346 a file; the existing copy is not deleted. (Note that if
347 an extension is given, an existing file is renamed to the backup
348 file, as is the case under other operating systems, so it does
349 not remain as a previous version under the original filename.)
353 If the C<"-S"> or C<-"S"> switch is present I<and> the script
354 name does not contain a directory, then Perl translates the
355 logical name DCL$PATH as a searchlist, using each translation
356 as a directory in which to look for the script. In addition,
357 if no file type is specified, Perl looks in each directory
358 for a file matching the name specified, with a blank type,
359 a type of F<.pl>, and a type of F<.com>, in that order.
363 The C<-u> switch causes the VMS debugger to be invoked
364 after the Perl program is compiled, but before it has
365 run. It does not create a core dump file.
369 =head1 Perl functions
371 As of the time this document was last revised, the following
372 Perl functions were implemented in the VMS port of Perl
373 (functions marked with * are discussed in more detail below):
375 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
376 caller, chdir, chmod, chown, chomp, chop, chr,
377 close, closedir, cos, crypt*, defined, delete,
378 die, do, dump*, each, endpwent, eof, eval, exec*,
379 exists, exit, exp, fileno, getc, getlogin, getppid,
380 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
381 grep, hex, import, index, int, join, keys, kill*,
382 last, lc, lcfirst, length, local, localtime, log, m//,
383 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
384 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
385 qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
386 require, reset, return, reverse, rewinddir, rindex,
387 rmdir, s///, scalar, seek, seekdir, select(internal),
388 select (system call)*, setpwent, shift, sin, sleep,
389 sort, splice, split, sprintf, sqrt, srand, stat,
390 study, substr, sysread, system*, syswrite, tell,
391 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
392 undef, unlink*, unpack, untie, unshift, use, utime*,
393 values, vec, wait, waitpid*, wantarray, warn, write, y///
395 The following functions were not implemented in the VMS port,
396 and calling them produces a fatal error (usually) or
397 undefined behavior (rarely, we hope):
399 chroot, dbmclose, dbmopen, flock, fork*,
400 getpgrp, getpriority, getgrent, getgrgid,
401 getgrnam, setgrent, endgrent, ioctl, link, lstat,
402 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
403 semget, semop, setpgrp, setpriority, shmctl, shmget,
404 shmread, shmwrite, socketpair, symlink, syscall
406 The following functions are available on Perls compiled with Dec C
407 5.2 or greater and running VMS 7.0 or greater:
411 The following functions are available on Perls built on VMS 7.2 or
414 fcntl (without locking)
416 The following functions may or may not be implemented,
417 depending on what type of socket support you've built into
420 accept, bind, connect, getpeername,
421 gethostbyname, getnetbyname, getprotobyname,
422 getservbyname, gethostbyaddr, getnetbyaddr,
423 getprotobynumber, getservbyport, gethostent,
424 getnetent, getprotoent, getservent, sethostent,
425 setnetent, setprotoent, setservent, endhostent,
426 endnetent, endprotoent, endservent, getsockname,
427 getsockopt, listen, recv, select(system call)*,
428 send, setsockopt, shutdown, socket
434 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
435 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
436 advertised. The return values for C<-r>, C<-w>, and C<-x>
437 tell you whether you can actually access the file; this may
438 not reflect the UIC-based file protections. Since real and
439 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
440 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
441 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
442 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
443 VMS, and the values returned by these tests reflect whatever
444 your CRTL C<stat()> routine does to the equivalent bits in the
445 st_mode field. Finally, C<-d> returns true if passed a device
446 specification without an explicit directory (e.g. C<DUA1:>), as
447 well as if passed a directory.
449 Note: Some sites have reported problems when using the file-access
450 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
451 Specifically, since DFS does not currently provide access to the
452 extended file header of files on remote volumes, attempts to
453 examine the ACL fail, and the file tests will return false,
454 with C<$!> indicating that the file does not exist. You can
455 use C<stat> on these files, since that checks UIC-based protection
456 only, and then manually check the appropriate bits, as defined by
457 your C compiler's F<stat.h>, in the mode value it returns, if you
458 need an approximation of the file's protections.
462 Backticks create a subprocess, and pass the enclosed string
463 to it for execution as a DCL command. Since the subprocess is
464 created directly via C<lib$spawn()>, any valid DCL command string
467 =item binmode FILEHANDLE
469 The C<binmode> operator will attempt to insure that no translation
470 of carriage control occurs on input from or output to this filehandle.
471 Since this involves reopening the file and then restoring its
472 file position indicator, if this function returns FALSE, the
473 underlying filehandle may no longer point to an open file, or may
474 point to a different position in the file than before C<binmode>
477 Note that C<binmode> is generally not necessary when using normal
478 filehandles; it is provided so that you can control I/O to existing
479 record-structured files when necessary. You can also use the
480 C<vmsfopen> function in the VMS::Stdio extension to gain finer
481 control of I/O to files and devices with different record structures.
483 =item crypt PLAINTEXT, USER
485 The C<crypt> operator uses the C<sys$hash_password> system
486 service to generate the hashed representation of PLAINTEXT.
487 If USER is a valid username, the algorithm and salt values
488 are taken from that user's UAF record. If it is not, then
489 the preferred algorithm and a salt of 0 are used. The
490 quadword encrypted value is returned as an 8-character string.
492 The value returned by C<crypt> may be compared against
493 the encrypted password from the UAF returned by the C<getpw*>
494 functions, in order to authenticate users. If you're
495 going to do this, remember that the encrypted password in
496 the UAF was generated using uppercase username and
497 password strings; you'll have to upcase the arguments to
498 C<crypt> to insure that you'll get the proper value:
500 sub validate_passwd {
501 my($user,$passwd) = @_;
503 if ( !($pwdhash = (getpwnam($user))[1]) ||
504 $pwdhash ne crypt("\U$passwd","\U$name") ) {
505 intruder_alert($name);
512 Rather than causing Perl to abort and dump core, the C<dump>
513 operator invokes the VMS debugger. If you continue to
514 execute the Perl program under the debugger, control will
515 be transferred to the label specified as the argument to
516 C<dump>, or, if no label was specified, back to the
517 beginning of the program. All other state of the program
518 (I<e.g.> values of variables, open file handles) are not
519 affected by calling C<dump>.
523 A call to C<exec> will cause Perl to exit, and to invoke the command
524 given as an argument to C<exec> via C<lib$do_command>. If the
525 argument begins with '@' or '$' (other than as part of a filespec),
526 then it is executed as a DCL command. Otherwise, the first token on
527 the command line is treated as the filespec of an image to run, and
528 an attempt is made to invoke it (using F<.Exe> and the process
529 defaults to expand the filespec) and pass the rest of C<exec>'s
530 argument to it as parameters. If the token has no file type, and
531 matches a file with null type, then an attempt is made to determine
532 whether the file is an executable image which should be invoked
533 using C<MCR> or a text file which should be passed to DCL as a
538 While in principle the C<fork> operator could be implemented via
539 (and with the same rather severe limitations as) the CRTL C<vfork()>
540 routine, and while some internal support to do just that is in
541 place, the implementation has never been completed, making C<fork>
542 currently unavailable. A true kernel C<fork()> is expected in a
543 future version of VMS, and the pseudo-fork based on interpreter
544 threads may be available in a future version of Perl on VMS (see
545 L<perlfork>). In the meantime, use C<system>, backticks, or piped
546 filehandles to create subprocesses.
554 These operators obtain the information described in L<perlfunc>,
555 if you have the privileges necessary to retrieve the named user's
556 UAF information via C<sys$getuai>. If not, then only the C<$name>,
557 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
558 the login directory in VMS syntax, while the C<$comment> item
559 contains the login directory in Unix syntax. The C<$gcos> item
560 contains the owner field from the UAF record. The C<$quota>
565 The C<gmtime> operator will function properly if you have a
566 working CRTL C<gmtime()> routine, or if the logical name
567 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
568 which must be added to UTC to yield local time. (This logical
569 name is defined automatically if you are running a version of
570 VMS with built-in UTC support.) If neither of these cases is
571 true, a warning message is printed, and C<undef> is returned.
575 In most cases, C<kill> is implemented via the CRTL's C<kill()>
576 function, so it will behave according to that function's
577 documentation. If you send a SIGKILL, however, the $DELPRC system
578 service is called directly. This insures that the target
579 process is actually deleted, if at all possible. (The CRTL's C<kill()>
580 function is presently implemented via $FORCEX, which is ignored by
581 supervisor-mode images like DCL.)
583 Also, negative signal values don't do anything special under
584 VMS; they're just converted to the corresponding positive value.
588 See the entry on C<backticks> above.
590 =item select (system call)
592 If Perl was not built with socket support, the system call
593 version of C<select> is not available at all. If socket
594 support is present, then the system call version of
595 C<select> functions only for file descriptors attached
596 to sockets. It will not provide information about regular
597 files or pipes, since the CRTL C<select()> routine does not
598 provide this functionality.
602 Since VMS keeps track of files according to a different scheme
603 than Unix, it's not really possible to represent the file's ID
604 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
605 tries its best, though, and the values it uses are pretty unlikely
606 to be the same for two different files. We can't guarantee this,
607 though, so caveat scriptor.
611 The C<system> operator creates a subprocess, and passes its
612 arguments to the subprocess for execution as a DCL command.
613 Since the subprocess is created directly via C<lib$spawn()>, any
614 valid DCL command string may be specified. If the string begins with
615 '@', it is treated as a DCL command unconditionally. Otherwise, if
616 the first token contains a character used as a delimiter in file
617 specification (e.g. C<:> or C<]>), an attempt is made to expand it
618 using a default type of F<.Exe> and the process defaults, and if
619 successful, the resulting file is invoked via C<MCR>. This allows you
620 to invoke an image directly simply by passing the file specification
621 to C<system>, a common Unixish idiom. If the token has no file type,
622 and matches a file with null type, then an attempt is made to
623 determine whether the file is an executable image which should be
624 invoked using C<MCR> or a text file which should be passed to DCL
625 as a command procedure.
627 If LIST consists of the empty string, C<system> spawns an
628 interactive DCL subprocess, in the same fashion as typing
629 B<SPAWN> at the DCL prompt.
631 Perl waits for the subprocess to complete before continuing
632 execution in the current process. As described in L<perlfunc>,
633 the return value of C<system> is a fake "status" which follows
634 POSIX semantics unless the pragma C<use vmsish 'status'> is in
635 effect; see the description of C<$?> in this document for more
640 The value returned by C<time> is the offset in seconds from
641 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
642 to make life easier for code coming in from the POSIX/Unix world.
646 The array returned by the C<times> operator is divided up
647 according to the same rules the CRTL C<times()> routine.
648 Therefore, the "system time" elements will always be 0, since
649 there is no difference between "user time" and "system" time
650 under VMS, and the time accumulated by a subprocess may or may
651 not appear separately in the "child time" field, depending on
652 whether L<times> keeps track of subprocesses separately. Note
653 especially that the VAXCRTL (at least) keeps track only of
654 subprocesses spawned using L<fork> and L<exec>; it will not
655 accumulate the times of subprocesses spawned via pipes, L<system>,
660 C<unlink> will delete the highest version of a file only; in
661 order to delete all versions, you need to say
665 You may need to make this change to scripts written for a
666 Unix system which expect that after a call to C<unlink>,
667 no files with the names passed to C<unlink> will exist.
668 (Note: This can be changed at compile time; if you
669 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
670 C<define>, then C<unlink> will delete all versions of a
671 file on the first call.)
673 C<unlink> will delete a file if at all possible, even if it
674 requires changing file protection (though it won't try to
675 change the protection of the parent directory). You can tell
676 whether you've got explicit delete access to a file by using the
677 C<VMS::Filespec::candelete> operator. For instance, in order
678 to delete only files to which you have delete access, you could
684 next unless VMS::Filespec::candelete($file);
685 $num += unlink $file;
690 (or you could just use C<VMS::Stdio::remove>, if you've installed
691 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
692 change the file protection to delete the file, and you interrupt it
693 in midstream, the file may be left intact, but with a changed ACL
694 allowing you delete access.
698 Since ODS-2, the VMS file structure for disk files, does not keep
699 track of access times, this operator changes only the modification
700 time of the file (VMS revision date).
702 =item waitpid PID,FLAGS
704 If PID is a subprocess started by a piped C<open()> (see L<open>),
705 C<waitpid> will wait for that subprocess, and return its final status
706 value in C<$?>. If PID is a subprocess created in some other way (e.g.
707 SPAWNed before Perl was invoked), C<waitpid> will simply check once per
708 second whether the process has completed, and return when it has. (If
709 PID specifies a process that isn't a subprocess of the current process,
710 and you invoked Perl with the C<-w> switch, a warning will be issued.)
712 Returns PID on success, -1 on error. The FLAGS argument is ignored
717 =head1 Perl variables
719 The following VMS-specific information applies to the indicated
720 "special" Perl variables, in addition to the general information
721 in L<perlvar>. Where there is a conflict, this information
728 The operation of the C<%ENV> array depends on the translation
729 of the logical name F<PERL_ENV_TABLES>. If defined, it should
730 be a search list, each element of which specifies a location
731 for C<%ENV> elements. If you tell Perl to read or set the
732 element C<$ENV{>I<name>C<}>, then Perl uses the translations of
733 F<PERL_ENV_TABLES> as follows:
739 This string tells Perl to consult the CRTL's internal C<environ>
740 array of key-value pairs, using I<name> as the key. In most cases,
741 this contains only a few keys, but if Perl was invoked via the C
742 C<exec[lv]e()> function, as is the case for CGI processing by some
743 HTTP servers, then the C<environ> array may have been populated by
748 A string beginning with C<CLISYM_>tells Perl to consult the CLI's
749 symbol tables, using I<name> as the name of the symbol. When reading
750 an element of C<%ENV>, the local symbol table is scanned first, followed
751 by the global symbol table.. The characters following C<CLISYM_> are
752 significant when an element of C<%ENV> is set or deleted: if the
753 complete string is C<CLISYM_LOCAL>, the change is made in the local
754 symbol table; otherwise the global symbol table is changed.
756 =item Any other string
758 If an element of F<PERL_ENV_TABLES> translates to any other string,
759 that string is used as the name of a logical name table, which is
760 consulted using I<name> as the logical name. The normal search
761 order of access modes is used.
765 F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
766 you make while Perl is running do not affect the behavior of C<%ENV>.
767 If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
768 first the logical name tables specified by F<LNM$FILE_DEV>, and then
769 the CRTL C<environ> array.
771 In all operations on %ENV, the key string is treated as if it
772 were entirely uppercase, regardless of the case actually
773 specified in the Perl expression.
775 When an element of C<%ENV> is read, the locations to which
776 F<PERL_ENV_TABLES> points are checked in order, and the value
777 obtained from the first successful lookup is returned. If the
778 name of the C<%ENV> element contains a semi-colon, it and
779 any characters after it are removed. These are ignored when
780 the CRTL C<environ> array or a CLI symbol table is consulted.
781 However, the name is looked up in a logical name table, the
782 suffix after the semi-colon is treated as the translation index
783 to be used for the lookup. This lets you look up successive values
784 for search list logical names. For instance, if you say
786 $ Define STORY once,upon,a,time,there,was
787 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
788 _$ -e "{ print $ENV{'story;'.$i},' '}"
790 Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
791 that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
792 is found, rather than a CLI symbol or CRTL C<environ> element with
795 When an element of C<%ENV> is set to a defined string, the
796 corresponding definition is made in the location to which the
797 first translation of F<PERL_ENV_TABLES> points. If this causes a
798 logical name to be created, it is defined in supervisor mode.
799 (The same is done if an existing logical name was defined in
800 executive or kernel mode; an existing user or supervisor mode
801 logical name is reset to the new value.) If the value is an empty
802 string, the logical name's translation is defined as a single NUL
803 (ASCII 00) character, since a logical name cannot translate to a
804 zero-length string. (This restriction does not apply to CLI symbols
805 or CRTL C<environ> values; they are set to the empty string.)
806 An element of the CRTL C<environ> array can be set only if your
807 copy of Perl knows about the CRTL's C<setenv()> function. (This is
808 present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
809 to see whether your copy of Perl was built with a CRTL that has this
812 When an element of C<%ENV> is set to C<undef>,
813 the element is looked up as if it were being read, and if it is
814 found, it is deleted. (An item "deleted" from the CRTL C<environ>
815 array is set to the empty string; this can only be done if your
816 copy of Perl knows about the CRTL C<setenv()> function.) Using
817 C<delete> to remove an element from C<%ENV> has a similar effect,
818 but after the element is deleted, another attempt is made to
819 look up the element, so an inner-mode logical name or a name in
820 another location will replace the logical name just deleted.
821 In either case, only the first value found searching PERL_ENV_TABLES
822 is altered. It is not possible at present to define a search list
823 logical name via %ENV.
825 The element C<$ENV{DEFAULT}> is special: when read, it returns
826 Perl's current default device and directory, and when set, it
827 resets them, regardless of the definition of F<PERL_ENV_TABLES>.
828 It cannot be cleared or deleted; attempts to do so are silently
831 Note that if you want to pass on any elements of the
832 C-local environ array to a subprocess which isn't
833 started by fork/exec, or isn't running a C program, you
834 can "promote" them to logical names in the current
835 process, which will then be inherited by all subprocesses,
838 foreach my $key (qw[C-local keys you want promoted]) {
839 my $temp = $ENV{$key}; # read from C-local array
840 $ENV{$key} = $temp; # and define as logical name
843 (You can't just say C<$ENV{$key} = $ENV{$key}>, since the
844 Perl optimizer is smart enough to elide the expression.)
846 Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
847 a fatal error. This is equivalent to doing the following from DCL:
851 You can imagine how bad things would be if, for example, the SYS$MANAGER
852 or SYS$SYSTEM logicals were deleted.
854 At present, the first time you iterate over %ENV using
855 C<keys>, or C<values>, you will incur a time penalty as all
856 logical names are read, in order to fully populate %ENV.
857 Subsequent iterations will not reread logical names, so they
858 won't be as slow, but they also won't reflect any changes
859 to logical name tables caused by other programs.
861 You do need to be careful with the logicals representing process-permanent
862 files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
863 logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
864 stripped off if you want to use it. (In previous versions of Perl it wasn't
865 possible to get the values of these logicals, as the null byte acted as an
866 end-of-string marker)
870 The string value of C<$!> is that returned by the CRTL's
871 strerror() function, so it will include the VMS message for
872 VMS-specific errors. The numeric value of C<$!> is the
873 value of C<errno>, except if errno is EVMSERR, in which
874 case C<$!> contains the value of vaxc$errno. Setting C<$!>
875 always sets errno to the value specified. If this value is
876 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
877 that the string value of C<$!> won't reflect the VMS error
878 message from before C<$!> was set.
882 This variable provides direct access to VMS status values
883 in vaxc$errno, which are often more specific than the
884 generic Unix-style error messages in C<$!>. Its numeric value
885 is the value of vaxc$errno, and its string value is the
886 corresponding VMS message string, as retrieved by sys$getmsg().
887 Setting C<$^E> sets vaxc$errno to the value specified.
891 The "status value" returned in C<$?> is synthesized from the
892 actual exit status of the subprocess in a way that approximates
893 POSIX wait(5) semantics, in order to allow Perl programs to
894 portably test for successful completion of subprocesses. The
895 low order 8 bits of C<$?> are always 0 under VMS, since the
896 termination status of a process may or may not have been
897 generated by an exception. The next 8 bits are derived from
898 the severity portion of the subprocess' exit status: if the
899 severity was success or informational, these bits are all 0;
900 if the severity was warning, they contain a value of 1; if the
901 severity was error or fatal error, they contain the actual
902 severity bits, which turns out to be a value of 2 for error
903 and 4 for fatal error.
905 As a result, C<$?> will always be zero if the subprocess' exit
906 status indicated successful completion, and non-zero if a
907 warning or error occurred. Conversely, when setting C<$?> in
908 an END block, an attempt is made to convert the POSIX value
909 into a native status intelligible to the operating system upon
910 exiting Perl. What this boils down to is that setting C<$?>
911 to zero results in the generic success value SS$_NORMAL, and
912 setting C<$?> to a non-zero value results in the generic
913 failure status SS$_ABORT. See also L<perlport/exit>.
915 The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
916 VMS exit status instead of the default emulation of POSIX status
917 described above. This pragma also disables the conversion of
918 non-zero values to SS$_ABORT when setting C<$?> in an END
919 block (but zero will still be converted to SS$_NORMAL).
923 Setting C<$|> for an I/O stream causes data to be flushed
924 all the way to disk on each write (I<i.e.> not just to
925 the underlying RMS buffers for a file). In other words,
926 it's equivalent to calling fflush() and fsync() from C.
930 =head1 Standard modules with VMS-specific differences
934 SDBM_File works properly on VMS. It has, however, one minor
935 difference. The database directory file created has a F<.sdbm_dir>
936 extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
937 directory files, and using them for other purposes could cause unacceptable
942 This document was last updated on 01-May-2002, for Perl 5,
947 Charles Bailey bailey@cor.newman.upenn.edu
948 Craig Berry craigberry@mac.com
949 Dan Sugalski dan@sidhe.org