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. C<E<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$spawn() for asynchronous
224 execution. You should be careful to close any pipes you have
225 opened in a Perl script, lest you leave any "orphaned"
226 subprocesses around when Perl exits.
228 You may also use backticks to invoke a DCL subprocess, whose
229 output is used as the return value of the expression. The
230 string between the backticks is handled as if it were the
231 argument to the C<system> operator (see below). In this case,
232 Perl will wait for the subprocess to complete before continuing.
234 The mailbox (MBX) that perl can create to communicate with a pipe
235 defaults to a buffer size of 512. The default buffer size is
236 adjustable via the logical name PERL_MBX_SIZE provided that the
237 value falls between 128 and the SYSGEN parameter MAXBUF inclusive.
238 For example, to double the MBX size from the default within
239 a Perl program, use C<$ENV{'PERL_MBX_SIZE'} = 1024;> and then
240 open and use pipe constructs. An alternative would be to issue
243 $ Define PERL_MBX_SIZE 1024
245 before running your wide record pipe program. A larger value may
246 improve performance at the expense of the BYTLM UAF quota.
248 =head1 PERL5LIB and PERLLIB
250 The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
251 except that the element separator is '|' instead of ':'. The
252 directory specifications may use either VMS or Unix syntax.
256 =head2 I/O redirection and backgrounding
258 Perl for VMS supports redirection of input and output on the
259 command line, using a subset of Bourne shell syntax:
265 C<E<lt>file> reads stdin from C<file>,
269 C<E<gt>file> writes stdout to C<file>,
273 C<E<gt>E<gt>file> appends stdout to C<file>,
277 C<2E<gt>file> writes stderr to C<file>, and
281 C<2E<gt>E<gt>file> appends stderr to C<file>.
285 In addition, output may be piped to a subprocess, using the
286 character '|'. Anything after this character on the command
287 line is passed to a subprocess for execution; the subprocess
288 takes the output of Perl as its input.
290 Finally, if the command line ends with '&', the entire
291 command is run in the background as an asynchronous
294 =head2 Command line switches
296 The following command line switches behave differently under
297 VMS than described in L<perlrun>. Note also that in order
298 to pass uppercase switches to Perl, you need to enclose
299 them in double-quotes on the command line, since the CRTL
300 downcases all unquoted strings.
306 If the C<-i> switch is present but no extension for a backup
307 copy is given, then inplace editing creates a new version of
308 a file; the existing copy is not deleted. (Note that if
309 an extension is given, an existing file is renamed to the backup
310 file, as is the case under other operating systems, so it does
311 not remain as a previous version under the original filename.)
315 If the C<"-S"> or C<-"S"> switch is present I<and> the script
316 name does not contain a directory, then Perl translates the
317 logical name DCL$PATH as a searchlist, using each translation
318 as a directory in which to look for the script. In addition,
319 if no file type is specified, Perl looks in each directory
320 for a file matching the name specified, with a blank type,
321 a type of F<.pl>, and a type of F<.com>, in that order.
325 The C<-u> switch causes the VMS debugger to be invoked
326 after the Perl program is compiled, but before it has
327 run. It does not create a core dump file.
331 =head1 Perl functions
333 As of the time this document was last revised, the following
334 Perl functions were implemented in the VMS port of Perl
335 (functions marked with * are discussed in more detail below):
337 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
338 caller, chdir, chmod, chown, chomp, chop, chr,
339 close, closedir, cos, crypt*, defined, delete,
340 die, do, dump*, each, endpwent, eof, eval, exec*,
341 exists, exit, exp, fileno, fork*, getc, getlogin,
342 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
343 grep, hex, import, index, int, join, keys, kill*,
344 last, lc, lcfirst, length, local, localtime, log, m//,
345 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
346 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
347 qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
348 require, reset, return, reverse, rewinddir, rindex,
349 rmdir, s///, scalar, seek, seekdir, select(internal),
350 select (system call)*, setpwent, shift, sin, sleep,
351 sort, splice, split, sprintf, sqrt, srand, stat,
352 study, substr, sysread, system*, syswrite, tell,
353 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
354 undef, unlink*, unpack, untie, unshift, use, utime*,
355 values, vec, wait, waitpid*, wantarray, warn, write, y///
357 The following functions were not implemented in the VMS port,
358 and calling them produces a fatal error (usually) or
359 undefined behavior (rarely, we hope):
361 chroot, dbmclose, dbmopen, flock,
362 getpgrp, getppid, getpriority, getgrent, getgrgid,
363 getgrnam, setgrent, endgrent, ioctl, link, lstat,
364 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
365 semget, semop, setpgrp, setpriority, shmctl, shmget,
366 shmread, shmwrite, socketpair, symlink, syscall
368 The following functions are available on Perls compiled with Dec C
369 5.2 or greater and running VMS 7.0 or greater:
373 The following functions are available on Perls built on VMS 7.2 or
376 fcntl (without locking)
378 The following functions may or may not be implemented,
379 depending on what type of socket support you've built into
382 accept, bind, connect, getpeername,
383 gethostbyname, getnetbyname, getprotobyname,
384 getservbyname, gethostbyaddr, getnetbyaddr,
385 getprotobynumber, getservbyport, gethostent,
386 getnetent, getprotoent, getservent, sethostent,
387 setnetent, setprotoent, setservent, endhostent,
388 endnetent, endprotoent, endservent, getsockname,
389 getsockopt, listen, recv, select(system call)*,
390 send, setsockopt, shutdown, socket
396 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
397 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
398 advertised. The return values for C<-r>, C<-w>, and C<-x>
399 tell you whether you can actually access the file; this may
400 not reflect the UIC-based file protections. Since real and
401 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
402 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
403 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
404 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
405 VMS, and the values returned by these tests reflect whatever
406 your CRTL C<stat()> routine does to the equivalent bits in the
407 st_mode field. Finally, C<-d> returns true if passed a device
408 specification without an explicit directory (e.g. C<DUA1:>), as
409 well as if passed a directory.
411 Note: Some sites have reported problems when using the file-access
412 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
413 Specifically, since DFS does not currently provide access to the
414 extended file header of files on remote volumes, attempts to
415 examine the ACL fail, and the file tests will return false,
416 with C<$!> indicating that the file does not exist. You can
417 use C<stat> on these files, since that checks UIC-based protection
418 only, and then manually check the appropriate bits, as defined by
419 your C compiler's F<stat.h>, in the mode value it returns, if you
420 need an approximation of the file's protections.
424 Backticks create a subprocess, and pass the enclosed string
425 to it for execution as a DCL command. Since the subprocess is
426 created directly via C<lib$spawn()>, any valid DCL command string
429 =item binmode FILEHANDLE
431 The C<binmode> operator will attempt to insure that no translation
432 of carriage control occurs on input from or output to this filehandle.
433 Since this involves reopening the file and then restoring its
434 file position indicator, if this function returns FALSE, the
435 underlying filehandle may no longer point to an open file, or may
436 point to a different position in the file than before C<binmode>
439 Note that C<binmode> is generally not necessary when using normal
440 filehandles; it is provided so that you can control I/O to existing
441 record-structured files when necessary. You can also use the
442 C<vmsfopen> function in the VMS::Stdio extension to gain finer
443 control of I/O to files and devices with different record structures.
445 =item crypt PLAINTEXT, USER
447 The C<crypt> operator uses the C<sys$hash_password> system
448 service to generate the hashed representation of PLAINTEXT.
449 If USER is a valid username, the algorithm and salt values
450 are taken from that user's UAF record. If it is not, then
451 the preferred algorithm and a salt of 0 are used. The
452 quadword encrypted value is returned as an 8-character string.
454 The value returned by C<crypt> may be compared against
455 the encrypted password from the UAF returned by the C<getpw*>
456 functions, in order to authenticate users. If you're
457 going to do this, remember that the encrypted password in
458 the UAF was generated using uppercase username and
459 password strings; you'll have to upcase the arguments to
460 C<crypt> to insure that you'll get the proper value:
462 sub validate_passwd {
463 my($user,$passwd) = @_;
465 if ( !($pwdhash = (getpwnam($user))[1]) ||
466 $pwdhash ne crypt("\U$passwd","\U$name") ) {
467 intruder_alert($name);
474 Rather than causing Perl to abort and dump core, the C<dump>
475 operator invokes the VMS debugger. If you continue to
476 execute the Perl program under the debugger, control will
477 be transferred to the label specified as the argument to
478 C<dump>, or, if no label was specified, back to the
479 beginning of the program. All other state of the program
480 (I<e.g.> values of variables, open file handles) are not
481 affected by calling C<dump>.
485 The C<exec> operator behaves in one of two different ways.
486 If called after a call to C<fork>, it will invoke the CRTL
487 C<execv()> routine, passing its arguments to the subprocess
488 created by C<fork> for execution. In this case, it is
489 subject to all limitations that affect C<execv()>. (In
490 particular, this usually means that the command executed in
491 the subprocess must be an image compiled from C source code,
492 and that your options for passing file descriptors and signal
493 handlers to the subprocess are limited.)
495 If the call to C<exec> does not follow a call to C<fork>, it
496 will cause Perl to exit, and to invoke the command given as
497 an argument to C<exec> via C<lib$do_command>. If the argument
498 begins with '@' or '$' (other than as part of a filespec), then it
499 is executed as a DCL command. Otherwise, the first token on
500 the command line is treated as the filespec of an image to
501 run, and an attempt is made to invoke it (using F<.Exe> and
502 the process defaults to expand the filespec) and pass the
503 rest of C<exec>'s argument to it as parameters. If the token
504 has no file type, and matches a file with null type, then an
505 attempt is made to determine whether the file is an executable
506 image which should be invoked using C<MCR> or a text file which
507 should be passed to DCL as a command procedure.
509 You can use C<exec> in both ways within the same script, as
510 long as you call C<fork> and C<exec> in pairs. Perl
511 keeps track of how many times C<fork> and C<exec> have been
512 called, and will call the CRTL C<execv()> routine if there have
513 previously been more calls to C<fork> than to C<exec>.
517 The C<fork> operator works in the same way as the CRTL
518 C<vfork()> routine, which is quite different under VMS than
519 under Unix. Specifically, while C<fork> returns 0 after it
520 is called and the subprocess PID after C<exec> is called, in
521 both cases the thread of execution is within the parent
522 process, so there is no opportunity to perform operations in
523 the subprocess before calling C<exec>.
525 In general, the use of C<fork> and C<exec> to create
526 subprocesses is not recommended under VMS; wherever possible,
527 use the C<system> operator or piped filehandles instead.
535 These operators obtain the information described in L<perlfunc>,
536 if you have the privileges necessary to retrieve the named user's
537 UAF information via C<sys$getuai>. If not, then only the C<$name>,
538 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
539 the login directory in VMS syntax, while the C<$comment> item
540 contains the login directory in Unix syntax. The C<$gcos> item
541 contains the owner field from the UAF record. The C<$quota>
546 The C<gmtime> operator will function properly if you have a
547 working CRTL C<gmtime()> routine, or if the logical name
548 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
549 which must be added to UTC to yield local time. (This logical
550 name is defined automatically if you are running a version of
551 VMS with built-in UTC support.) If neither of these cases is
552 true, a warning message is printed, and C<undef> is returned.
556 In most cases, C<kill> is implemented via the CRTL's C<kill()>
557 function, so it will behave according to that function's
558 documentation. If you send a SIGKILL, however, the $DELPRC system
559 service is called directly. This insures that the target
560 process is actually deleted, if at all possible. (The CRTL's C<kill()>
561 function is presently implemented via $FORCEX, which is ignored by
562 supervisor-mode images like DCL.)
564 Also, negative signal values don't do anything special under
565 VMS; they're just converted to the corresponding positive value.
569 See the entry on C<backticks> above.
571 =item select (system call)
573 If Perl was not built with socket support, the system call
574 version of C<select> is not available at all. If socket
575 support is present, then the system call version of
576 C<select> functions only for file descriptors attached
577 to sockets. It will not provide information about regular
578 files or pipes, since the CRTL C<select()> routine does not
579 provide this functionality.
583 Since VMS keeps track of files according to a different scheme
584 than Unix, it's not really possible to represent the file's ID
585 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
586 tries its best, though, and the values it uses are pretty unlikely
587 to be the same for two different files. We can't guarantee this,
588 though, so caveat scriptor.
592 The C<system> operator creates a subprocess, and passes its
593 arguments to the subprocess for execution as a DCL command.
594 Since the subprocess is created directly via C<lib$spawn()>, any
595 valid DCL command string may be specified. If the string begins with
596 '@', it is treated as a DCL command unconditionally. Otherwise, if
597 the first token contains a character used as a delimiter in file
598 specification (e.g. C<:> or C<]>), an attempt is made to expand it
599 using a default type of F<.Exe> and the process defaults, and if
600 successful, the resulting file is invoked via C<MCR>. This allows you
601 to invoke an image directly simply by passing the file specification
602 to C<system>, a common Unixish idiom. If the token has no file type,
603 and matches a file with null type, then an attempt is made to
604 determine whether the file is an executable image which should be
605 invoked using C<MCR> or a text file which should be passed to DCL
606 as a command procedure.
608 If LIST consists of the empty string, C<system> spawns an
609 interactive DCL subprocess, in the same fashion as typing
610 B<SPAWN> at the DCL prompt.
612 Perl waits for the subprocess to complete before continuing
613 execution in the current process. As described in L<perlfunc>,
614 the return value of C<system> is a fake "status" which follows
615 POSIX semantics unless the pragma C<use vmsish 'status'> is in
616 effect; see the description of C<$?> in this document for more
621 The value returned by C<time> is the offset in seconds from
622 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
623 to make life easier for code coming in from the POSIX/Unix world.
627 The array returned by the C<times> operator is divided up
628 according to the same rules the CRTL C<times()> routine.
629 Therefore, the "system time" elements will always be 0, since
630 there is no difference between "user time" and "system" time
631 under VMS, and the time accumulated by a subprocess may or may
632 not appear separately in the "child time" field, depending on
633 whether L<times> keeps track of subprocesses separately. Note
634 especially that the VAXCRTL (at least) keeps track only of
635 subprocesses spawned using L<fork> and L<exec>; it will not
636 accumulate the times of subprocesses spawned via pipes, L<system>,
641 C<unlink> will delete the highest version of a file only; in
642 order to delete all versions, you need to say
646 You may need to make this change to scripts written for a
647 Unix system which expect that after a call to C<unlink>,
648 no files with the names passed to C<unlink> will exist.
649 (Note: This can be changed at compile time; if you
650 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
651 C<define>, then C<unlink> will delete all versions of a
652 file on the first call.)
654 C<unlink> will delete a file if at all possible, even if it
655 requires changing file protection (though it won't try to
656 change the protection of the parent directory). You can tell
657 whether you've got explicit delete access to a file by using the
658 C<VMS::Filespec::candelete> operator. For instance, in order
659 to delete only files to which you have delete access, you could
665 next unless VMS::Filespec::candelete($file);
666 $num += unlink $file;
671 (or you could just use C<VMS::Stdio::remove>, if you've installed
672 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
673 change the file protection to delete the file, and you interrupt it
674 in midstream, the file may be left intact, but with a changed ACL
675 allowing you delete access.
679 Since ODS-2, the VMS file structure for disk files, does not keep
680 track of access times, this operator changes only the modification
681 time of the file (VMS revision date).
683 =item waitpid PID,FLAGS
685 If PID is a subprocess started by a piped C<open()> (see L<open>),
686 C<waitpid> will wait for that subprocess, and return its final status
687 value in C<$?>. If PID is a subprocess created in some other way (e.g.
688 SPAWNed before Perl was invoked), C<waitpid> will simply check once per
689 second whether the process has completed, and return when it has. (If
690 PID specifies a process that isn't a subprocess of the current process,
691 and you invoked Perl with the C<-w> switch, a warning will be issued.)
693 Returns PID on success, -1 on error. The FLAGS argument is ignored
698 =head1 Perl variables
700 The following VMS-specific information applies to the indicated
701 "special" Perl variables, in addition to the general information
702 in L<perlvar>. Where there is a conflict, this information
709 The operation of the C<%ENV> array depends on the translation
710 of the logical name F<PERL_ENV_TABLES>. If defined, it should
711 be a search list, each element of which specifies a location
712 for C<%ENV> elements. If you tell Perl to read or set the
713 element C<$ENV{>I<name>C<}>, then Perl uses the translations of
714 F<PERL_ENV_TABLES> as follows:
720 This string tells Perl to consult the CRTL's internal C<environ>
721 array of key-value pairs, using I<name> as the key. In most cases,
722 this contains only a few keys, but if Perl was invoked via the C
723 C<exec[lv]e()> function, as is the case for CGI processing by some
724 HTTP servers, then the C<environ> array may have been populated by
729 A string beginning with C<CLISYM_>tells Perl to consult the CLI's
730 symbol tables, using I<name> as the name of the symbol. When reading
731 an element of C<%ENV>, the local symbol table is scanned first, followed
732 by the global symbol table.. The characters following C<CLISYM_> are
733 significant when an element of C<%ENV> is set or deleted: if the
734 complete string is C<CLISYM_LOCAL>, the change is made in the local
735 symbol table; otherwise the global symbol table is changed.
737 =item Any other string
739 If an element of F<PERL_ENV_TABLES> translates to any other string,
740 that string is used as the name of a logical name table, which is
741 consulted using I<name> as the logical name. The normal search
742 order of access modes is used.
746 F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
747 you make while Perl is running do not affect the behavior of C<%ENV>.
748 If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
749 first the logical name tables specified by F<LNM$FILE_DEV>, and then
750 the CRTL C<environ> array.
752 In all operations on %ENV, the key string is treated as if it
753 were entirely uppercase, regardless of the case actually
754 specified in the Perl expression.
756 When an element of C<%ENV> is read, the locations to which
757 F<PERL_ENV_TABLES> points are checked in order, and the value
758 obtained from the first successful lookup is returned. If the
759 name of the C<%ENV> element contains a semi-colon, it and
760 any characters after it are removed. These are ignored when
761 the CRTL C<environ> array or a CLI symbol table is consulted.
762 However, the name is looked up in a logical name table, the
763 suffix after the semi-colon is treated as the translation index
764 to be used for the lookup. This lets you look up successive values
765 for search list logical names. For instance, if you say
767 $ Define STORY once,upon,a,time,there,was
768 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
769 _$ -e "{ print $ENV{'story;'.$i},' '}"
771 Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
772 that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
773 is found, rather than a CLI symbol or CRTL C<environ> element with
776 When an element of C<%ENV> is set to a defined string, the
777 corresponding definition is made in the location to which the
778 first translation of F<PERL_ENV_TABLES> points. If this causes a
779 logical name to be created, it is defined in supervisor mode.
780 (The same is done if an existing logical name was defined in
781 executive or kernel mode; an existing user or supervisor mode
782 logical name is reset to the new value.) If the value is an empty
783 string, the logical name's translation is defined as a single NUL
784 (ASCII 00) character, since a logical name cannot translate to a
785 zero-length string. (This restriction does not apply to CLI symbols
786 or CRTL C<environ> values; they are set to the empty string.)
787 An element of the CRTL C<environ> array can be set only if your
788 copy of Perl knows about the CRTL's C<setenv()> function. (This is
789 present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
790 to see whether your copy of Perl was built with a CRTL that has this
793 When an element of C<%ENV> is set to C<undef>,
794 the element is looked up as if it were being read, and if it is
795 found, it is deleted. (An item "deleted" from the CRTL C<environ>
796 array is set to the empty string; this can only be done if your
797 copy of Perl knows about the CRTL C<setenv()> function.) Using
798 C<delete> to remove an element from C<%ENV> has a similar effect,
799 but after the element is deleted, another attempt is made to
800 look up the element, so an inner-mode logical name or a name in
801 another location will replace the logical name just deleted.
802 In either case, only the first value found searching PERL_ENV_TABLES
803 is altered. It is not possible at present to define a search list
804 logical name via %ENV.
806 The element C<$ENV{DEFAULT}> is special: when read, it returns
807 Perl's current default device and directory, and when set, it
808 resets them, regardless of the definition of F<PERL_ENV_TABLES>.
809 It cannot be cleared or deleted; attempts to do so are silently
812 Note that if you want to pass on any elements of the
813 C-local environ array to a subprocess which isn't
814 started by fork/exec, or isn't running a C program, you
815 can "promote" them to logical names in the current
816 process, which will then be inherited by all subprocesses,
819 foreach my $key (qw[C-local keys you want promoted]) {
820 my $temp = $ENV{$key}; # read from C-local array
821 $ENV{$key} = $temp; # and define as logical name
824 (You can't just say C<$ENV{$key} = $ENV{$key}>, since the
825 Perl optimizer is smart enough to elide the expression.)
827 Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
828 a fatal error. This is equivalent to doing the following from DCL:
832 You can imagine how bad things would be if, for example, the SYS$MANAGER
833 or SYS$SYSTEM logicals were deleted.
835 At present, the first time you iterate over %ENV using
836 C<keys>, or C<values>, you will incur a time penalty as all
837 logical names are read, in order to fully populate %ENV.
838 Subsequent iterations will not reread logical names, so they
839 won't be as slow, but they also won't reflect any changes
840 to logical name tables caused by other programs.
842 You do need to be careful with the logicals representing process-permanent
843 files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
844 logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
845 stripped off if you want to use it. (In previous versions of Perl it wasn't
846 possible to get the values of these logicals, as the null byte acted as an
847 end-of-string marker)
851 The string value of C<$!> is that returned by the CRTL's
852 strerror() function, so it will include the VMS message for
853 VMS-specific errors. The numeric value of C<$!> is the
854 value of C<errno>, except if errno is EVMSERR, in which
855 case C<$!> contains the value of vaxc$errno. Setting C<$!>
856 always sets errno to the value specified. If this value is
857 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
858 that the string value of C<$!> won't reflect the VMS error
859 message from before C<$!> was set.
863 This variable provides direct access to VMS status values
864 in vaxc$errno, which are often more specific than the
865 generic Unix-style error messages in C<$!>. Its numeric value
866 is the value of vaxc$errno, and its string value is the
867 corresponding VMS message string, as retrieved by sys$getmsg().
868 Setting C<$^E> sets vaxc$errno to the value specified.
872 The "status value" returned in C<$?> is synthesized from the
873 actual exit status of the subprocess in a way that approximates
874 POSIX wait(5) semantics, in order to allow Perl programs to
875 portably test for successful completion of subprocesses. The
876 low order 8 bits of C<$?> are always 0 under VMS, since the
877 termination status of a process may or may not have been
878 generated by an exception. The next 8 bits are derived from
879 the severity portion of the subprocess' exit status: if the
880 severity was success or informational, these bits are all 0;
881 if the severity was warning, they contain a value of 1; if the
882 severity was error or fatal error, they contain the actual
883 severity bits, which turns out to be a value of 2 for error
884 and 4 for fatal error.
886 As a result, C<$?> will always be zero if the subprocess' exit
887 status indicated successful completion, and non-zero if a
888 warning or error occurred. Conversely, when setting C<$?> in
889 an END block, an attempt is made to convert the POSIX value
890 into a native status intelligible to the operating system upon
891 exiting Perl. What this boils down to is that setting C<$?>
892 to zero results in the generic success value SS$_NORMAL, and
893 setting C<$?> to a non-zero value results in the generic
894 failure status SS$_ABORT. See also L<perlport/exit>.
896 The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
897 VMS exit status instead of the default emulation of POSIX status
898 described above. This pragma also disables the conversion of
899 non-zero values to SS$_ABORT when setting C<$?> in an END
900 block (but zero will still be converted to SS$_NORMAL).
904 Setting C<$|> for an I/O stream causes data to be flushed
905 all the way to disk on each write (I<i.e.> not just to
906 the underlying RMS buffers for a file). In other words,
907 it's equivalent to calling fflush() and fsync() from C.
911 =head1 Standard modules with VMS-specific differences
915 SDBM_File works properly on VMS. It has, however, one minor
916 difference. The database directory file created has a F<.sdbm_dir>
917 extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
918 directory files, and using them for other purposes could cause unacceptable
923 This document was last updated on 01-May-2002, for Perl 5,
928 Charles Bailey bailey@cor.newman.upenn.edu
929 Craig Berry craigberry@mac.com
930 Dan Sugalski dan@sidhe.org