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 build 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 XS extensions and has a hard-wired list of library locations
36 for loading pure-Perl modules. It is used extensively to build and
37 test Perl and various extensions, but is not installed.
39 Most of the complete Perl resides in the shareable image F<PerlShr.Exe>,
40 which provides a core to which the Perl executable image and all Perl
41 extensions are linked. It is generally located via the logical name
42 F<PERLSHR>. While it's possible to put the image in F<SYS$SHARE> to
43 make it loadable, that's not recommended. And while you may wish to
44 INSTALL the image for performance reasons, you should not install it
45 with privileges; if you do, the result will not be what you expect as
46 image privileges are disabled during Perl start-up.
48 Finally, F<Perl.Exe> is an executable image containing the main
49 entry point for Perl, as well as some initialization code. It
50 should be placed in a public directory, and made world executable.
51 In order to run Perl with command line arguments, you should
52 define a foreign command to invoke this image.
54 =head2 Perl Extensions
56 Perl extensions are packages which provide both XS and Perl code
57 to add new functionality to perl. (XS is a meta-language which
58 simplifies writing C code which interacts with Perl, see
59 L<perlxs> for more details.) The Perl code for an
60 extension is treated like any other library module - it's
61 made available in your script through the appropriate
62 C<use> or C<require> statement, and usually defines a Perl
63 package containing the extension.
65 The portion of the extension provided by the XS code may be
66 connected to the rest of Perl in either of two ways. In the
67 B<static> configuration, the object code for the extension is
68 linked directly into F<PerlShr.Exe>, and is initialized whenever
69 Perl is invoked. In the B<dynamic> configuration, the extension's
70 machine code is placed into a separate shareable image, which is
71 mapped by Perl's DynaLoader when the extension is C<use>d or
72 C<require>d in your script. This allows you to maintain the
73 extension as a separate entity, at the cost of keeping track of the
74 additional shareable image. Most extensions can be set up as either
77 The source code for an extension usually resides in its own
78 directory. At least three files are generally provided:
79 I<Extshortname>F<.xs> (where I<Extshortname> is the portion of
80 the extension's name following the last C<::>), containing
81 the XS code, I<Extshortname>F<.pm>, the Perl library module
82 for the extension, and F<Makefile.PL>, a Perl script which uses
83 the C<MakeMaker> library modules supplied with Perl to generate
84 a F<Descrip.MMS> file for the extension.
86 =head2 Installing static extensions
88 Since static extensions are incorporated directly into
89 F<PerlShr.Exe>, you'll have to rebuild Perl to incorporate a
90 new extension. You should edit the main F<Descrip.MMS> or F<Makefile>
91 you use to build Perl, adding the extension's name to the C<ext>
92 macro, and the extension's object file to the C<extobj> macro.
93 You'll also need to build the extension's object file, either
94 by adding dependencies to the main F<Descrip.MMS>, or using a
95 separate F<Descrip.MMS> for the extension. Then, rebuild
96 F<PerlShr.Exe> to incorporate the new code.
98 Finally, you'll need to copy the extension's Perl library
99 module to the F<[.>I<Extname>F<]> subdirectory under one
100 of the directories in C<@INC>, where I<Extname> is the name
101 of the extension, with all C<::> replaced by C<.> (e.g.
102 the library module for extension Foo::Bar would be copied
103 to a F<[.Foo.Bar]> subdirectory).
105 =head2 Installing dynamic extensions
107 In general, the distributed kit for a Perl extension includes
108 a file named Makefile.PL, which is a Perl program which is used
109 to create a F<Descrip.MMS> file which can be used to build and
110 install the files required by the extension. The kit should be
111 unpacked into a directory tree B<not> under the main Perl source
112 directory, and the procedure for building the extension is simply
114 $ perl Makefile.PL ! Create Descrip.MMS
115 $ mmk ! Build necessary files
116 $ mmk test ! Run test code, if supplied
117 $ mmk install ! Install into public Perl tree
119 VMS support for this process in the current release of Perl
120 is sufficient to handle most extensions. (See the MakeMaker
121 documentation for more details on installation options for
128 the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
129 of one of the directories in C<@INC> (where I<PVers>
130 is the version of Perl you're using, as supplied in C<$]>,
131 with '.' converted to '_'), or
135 one of the directories in C<@INC>, or
139 a directory which the extensions Perl library module
140 passes to the DynaLoader when asking it to map
141 the shareable image, or
145 F<Sys$Share> or F<Sys$Library>.
149 If the shareable image isn't in any of these places, you'll need
150 to define a logical name I<Extshortname>, where I<Extshortname>
151 is the portion of the extension's name after the last C<::>, which
152 translates to the full file specification of the shareable image.
154 =head1 File specifications
158 We have tried to make Perl aware of both VMS-style and Unix-style file
159 specifications wherever possible. You may use either style, or both,
160 on the command line and in scripts, but you may not combine the two
161 styles within a single file specification. VMS Perl interprets Unix
162 pathnames in much the same way as the CRTL (I<e.g.> the first component
163 of an absolute path is read as the device name for the VMS file
164 specification). There are a set of functions provided in the
165 C<VMS::Filespec> package for explicit interconversion between VMS and
166 Unix syntax; its documentation provides more details.
168 We've tried to minimize the dependence of Perl library
169 modules on Unix syntax, but you may find that some of these,
170 as well as some scripts written for Unix systems, will
171 require that you use Unix syntax, since they will assume that
172 '/' is the directory separator, I<etc.> If you find instances
173 of this in the Perl distribution itself, please let us know,
174 so we can try to work around them.
176 Also when working on Perl programs on VMS, if you need a syntax
177 in a specific operating system format, then you need either to
178 check the appropriate DECC$ feature logical, or call a conversion
179 routine to force it to that format.
181 The feature logical name DECC$FILENAME_UNIX_REPORT modifies traditional
182 Perl behavior in the conversion of file specifications from Unix to VMS
183 format in order to follow the extended character handling rules now
184 expected by the CRTL. Specifically, when this feature is in effect, the
185 C<./.../> in a Unix path is now translated to C<[.^.^.^.]> instead of
186 the traditional VMS C<[...]>. To be compatible with what MakeMaker
187 expects, if a VMS path cannot be translated to a Unix path, it is
188 passed through unchanged, so C<unixify("[...]")> will return C<[...]>.
190 There are several ambiguous cases where a conversion routine cannot
191 determine whether an input filename is in Unix format or in VMS format,
192 since now both VMS and Unix file specifications may have characters in
193 them that could be mistaken for syntax delimiters of the other type. So
194 some pathnames simply cannot be used in a mode that allows either type
195 of pathname to be present. Perl will tend to assume that an ambiguous
196 filename is in Unix format.
198 Allowing "." as a version delimiter is simply incompatible with
199 determining whether a pathname is in VMS format or in Unix format with
200 extended file syntax. There is no way to know whether "perl-5.8.6" is a
201 Unix "perl-5.8.6" or a VMS "perl-5.8;6" when passing it to unixify() or
204 The DECC$FILENAME_UNIX_REPORT logical name controls how Perl interprets
205 filenames to the extent that Perl uses the CRTL internally for many
206 purposes, and attempts to follow CRTL conventions for reporting
207 filenames. The DECC$FILENAME_UNIX_ONLY feature differs in that it
208 expects all filenames passed to the C run-time to be already in Unix
209 format. This feature is not yet supported in Perl since Perl uses
210 traditional OpenVMS file specifications internally and in the test
211 harness, and it is not yet clear whether this mode will be useful or
212 useable. The feature logical name DECC$POSIX_COMPLIANT_PATHNAMES is new
213 with the RMS Symbolic Link SDK and included with OpenVMS v8.3, but is
214 not yet supported in Perl.
218 Perl enables DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE by
219 default. Note that the latter only takes effect when extended parse
220 is set in the process in which Perl is running. When these features
221 are explicitly disabled in the environment or the CRTL does not support
222 them, Perl follows the traditional CRTL behavior of downcasing command-line
223 arguments and returning file specifications in lower case only.
225 I<N. B.> It is very easy to get tripped up using a mixture of other
226 programs, external utilities, and Perl scripts that are in varying
227 states of being able to handle case preservation. For example, a file
228 created by an older version of an archive utility or a build utility
229 such as MMK or MMS may generate a filename in all upper case even on an
230 ODS-5 volume. If this filename is later retrieved by a Perl script or
231 module in a case preserving environment, that upper case name may not
232 match the mixed-case or lower-case expectations of the Perl code. Your
233 best bet is to follow an all-or-nothing approach to case preservation:
234 either don't use it at all, or make sure your entire toolchain and
235 application environment support and use it.
237 OpenVMS Alpha v7.3-1 and later and all version of OpenVMS I64 support
238 case sensitivity as a process setting (see C<SET PROCESS
239 /CASE_LOOKUP=SENSITIVE>). Perl does not currently support case
240 sensitivity on VMS, but it may in the future, so Perl programs should
241 use the C<< File::Spec->case_tolerant >> method to determine the state, and
242 not the C<$^O> variable.
244 =head2 Symbolic Links
246 When built on an ODS-5 volume with symbolic links enabled, Perl by
247 default supports symbolic links when the requisite support is available
248 in the filesystem and CRTL (generally 64-bit OpenVMS v8.3 and later).
249 There are a number of limitations and caveats to be aware of when
250 working with symbolic links on VMS. Most notably, the target of a valid
251 symbolic link must be expressed as a Unix-style path and it must exist
252 on a volume visible from your POSIX root (see the C<SHOW ROOT> command
253 in DCL help). For further details on symbolic link capabilities and
254 requirements, see chapter 12 of the CRTL manual that ships with OpenVMS
257 =head2 Wildcard expansion
259 File specifications containing wildcards are allowed both on
260 the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>). If
261 the wildcard filespec uses VMS syntax, the resultant
262 filespecs will follow VMS syntax; if a Unix-style filespec is
263 passed in, Unix-style filespecs will be returned.
264 Similar to the behavior of wildcard globbing for a Unix shell,
265 one can escape command line wildcards with double quotation
266 marks C<"> around a perl program command line argument. However,
267 owing to the stripping of C<"> characters carried out by the C
268 handling of argv you will need to escape a construct such as
269 this one (in a directory containing the files F<PERL.C>, F<PERL.EXE>,
270 F<PERL.H>, and F<PERL.OBJ>):
272 $ perl -e "print join(' ',@ARGV)" perl.*
273 perl.c perl.exe perl.h perl.obj
275 in the following triple quoted manner:
277 $ perl -e "print join(' ',@ARGV)" """perl.*"""
280 In both the case of unquoted command line arguments or in calls
281 to C<glob()> VMS wildcard expansion is performed. (csh-style
282 wildcard expansion is available if you use C<File::Glob::glob>.)
283 If the wildcard filespec contains a device or directory
284 specification, then the resultant filespecs will also contain
285 a device and directory; otherwise, device and directory
286 information are removed. VMS-style resultant filespecs will
287 contain a full device and directory, while Unix-style
288 resultant filespecs will contain only as much of a directory
289 path as was present in the input filespec. For example, if
290 your default directory is Perl_Root:[000000], the expansion
291 of C<[.t]*.*> will yield filespecs like
292 "perl_root:[t]base.dir", while the expansion of C<t/*/*> will
293 yield filespecs like "t/base.dir". (This is done to match
294 the behavior of glob expansion performed by Unix shells.)
296 Similarly, the resultant filespec will contain the file version
297 only if one was present in the input filespec.
302 Input and output pipes to Perl filehandles are supported; the
303 "file name" is passed to lib$spawn() for asynchronous
304 execution. You should be careful to close any pipes you have
305 opened in a Perl script, lest you leave any "orphaned"
306 subprocesses around when Perl exits.
308 You may also use backticks to invoke a DCL subprocess, whose
309 output is used as the return value of the expression. The
310 string between the backticks is handled as if it were the
311 argument to the C<system> operator (see below). In this case,
312 Perl will wait for the subprocess to complete before continuing.
314 The mailbox (MBX) that perl can create to communicate with a pipe
315 defaults to a buffer size of 8192 on 64-bit systems, 512 on VAX. The
316 default buffer size is adjustable via the logical name PERL_MBX_SIZE
317 provided that the value falls between 128 and the SYSGEN parameter
318 MAXBUF inclusive. For example, to set the mailbox size to 32767 use
319 C<$ENV{'PERL_MBX_SIZE'} = 32767;> and then open and use pipe constructs.
320 An alternative would be to issue the command:
322 $ Define PERL_MBX_SIZE 32767
324 before running your wide record pipe program. A larger value may
325 improve performance at the expense of the BYTLM UAF quota.
327 =head1 PERL5LIB and PERLLIB
329 The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
330 except that the element separator is '|' instead of ':'. The
331 directory specifications may use either VMS or Unix syntax.
333 =head1 The Perl Forked Debugger
335 The Perl forked debugger places the debugger commands and output in a
336 separate X-11 terminal window so that commands and output from multiple
337 processes are not mixed together.
339 Perl on VMS supports an emulation of the forked debugger when Perl is
340 run on a VMS system that has X11 support installed.
342 To use the forked debugger, you need to have the default display set to an
343 X-11 Server and some environment variables set that Unix expects.
345 The forked debugger requires the environment variable C<TERM> to be C<xterm>,
346 and the environment variable C<DISPLAY> to exist. C<xterm> must be in
351 $define DISPLAY "hostname:0.0"
353 Currently the value of C<DISPLAY> is ignored. It is recommended that it be set
354 to be the hostname of the display, the server and screen in Unix notation. In
355 the future the value of DISPLAY may be honored by Perl instead of using the
358 It may be helpful to always use the forked debugger so that script I/O is
359 separated from debugger I/O. You can force the debugger to be forked by
360 assigning a value to the logical name <PERLDB_PIDS> that is not a process
361 identification number.
363 $define PERLDB_PIDS XXXX
366 =head1 PERL_VMS_EXCEPTION_DEBUG
368 The PERL_VMS_EXCEPTION_DEBUG being defined as "ENABLE" will cause the VMS
369 debugger to be invoked if a fatal exception that is not otherwise
370 handled is raised. The purpose of this is to allow debugging of
371 internal Perl problems that would cause such a condition.
373 This allows the programmer to look at the execution stack and variables to
374 find out the cause of the exception. As the debugger is being invoked as
375 the Perl interpreter is about to do a fatal exit, continuing the execution
376 in debug mode is usually not practical.
378 Starting Perl in the VMS debugger may change the program execution
379 profile in a way that such problems are not reproduced.
381 The C<kill> function can be used to test this functionality from within
384 In typical VMS style, only the first letter of the value of this logical
385 name is actually checked in a case insensitive mode, and it is considered
386 enabled if it is the value "T","1" or "E".
388 This logical name must be defined before Perl is started.
392 =head2 I/O redirection and backgrounding
394 Perl for VMS supports redirection of input and output on the
395 command line, using a subset of Bourne shell syntax:
401 C<E<lt>file> reads stdin from C<file>,
405 C<E<gt>file> writes stdout to C<file>,
409 C<E<gt>E<gt>file> appends stdout to C<file>,
413 C<2E<gt>file> writes stderr to C<file>,
417 C<2E<gt>E<gt>file> appends stderr to C<file>, and
421 C<< 2>&1 >> redirects stderr to stdout.
425 In addition, output may be piped to a subprocess, using the
426 character '|'. Anything after this character on the command
427 line is passed to a subprocess for execution; the subprocess
428 takes the output of Perl as its input.
430 Finally, if the command line ends with '&', the entire
431 command is run in the background as an asynchronous
434 =head2 Command line switches
436 The following command line switches behave differently under
437 VMS than described in L<perlrun>. Note also that in order
438 to pass uppercase switches to Perl, you need to enclose
439 them in double-quotes on the command line, since the CRTL
440 downcases all unquoted strings.
442 On newer 64 bit versions of OpenVMS, a process setting now
443 controls if the quoting is needed to preserve the case of
444 command line arguments.
450 If the C<-i> switch is present but no extension for a backup
451 copy is given, then inplace editing creates a new version of
452 a file; the existing copy is not deleted. (Note that if
453 an extension is given, an existing file is renamed to the backup
454 file, as is the case under other operating systems, so it does
455 not remain as a previous version under the original filename.)
459 If the C<"-S"> or C<-"S"> switch is present I<and> the script
460 name does not contain a directory, then Perl translates the
461 logical name DCL$PATH as a searchlist, using each translation
462 as a directory in which to look for the script. In addition,
463 if no file type is specified, Perl looks in each directory
464 for a file matching the name specified, with a blank type,
465 a type of F<.pl>, and a type of F<.com>, in that order.
469 The C<-u> switch causes the VMS debugger to be invoked
470 after the Perl program is compiled, but before it has
471 run. It does not create a core dump file.
475 =head1 Perl functions
477 As of the time this document was last revised, the following
478 Perl functions were implemented in the VMS port of Perl
479 (functions marked with * are discussed in more detail below):
481 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
482 caller, chdir, chmod, chown, chomp, chop, chr,
483 close, closedir, cos, crypt*, defined, delete, die, do, dump*,
484 each, endgrent, endpwent, eof, eval, exec*, exists, exit, exp,
485 fileno, flock getc, getgrent*, getgrgid*, getgrnam, getlogin,
486 getppid, getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
487 grep, hex, ioctl, import, index, int, join, keys, kill*,
488 last, lc, lcfirst, lchown*, length, link*, local, localtime, log,
489 lstat, m//, map, mkdir, my, next, no, oct, open, opendir, ord,
490 pack, pipe, pop, pos, print, printf, push, q//, qq//, qw//,
491 qx//*, quotemeta, rand, read, readdir, readlink*, redo, ref,
492 rename, require, reset, return, reverse, rewinddir, rindex,
493 rmdir, s///, scalar, seek, seekdir, select(internal),
494 select (system call)*, setgrent, setpwent, shift, sin, sleep,
495 socketpair, sort, splice, split, sprintf, sqrt, srand, stat,
496 study, substr, symlink*, sysread, system*, syswrite, tell,
497 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
498 undef, unlink*, unpack, untie, unshift, use, utime*,
499 values, vec, wait, waitpid*, wantarray, warn, write, y///
501 The following functions were not implemented in the VMS port,
502 and calling them produces a fatal error (usually) or
503 undefined behavior (rarely, we hope):
505 chroot, dbmclose, dbmopen, fork*, getpgrp, getpriority,
506 msgctl, msgget, msgsend, msgrcv, semctl,
507 semget, semop, setpgrp, setpriority, shmctl, shmget,
508 shmread, shmwrite, syscall
510 The following functions are available on Perls compiled with Dec C
511 5.2 or greater and running VMS 7.0 or greater:
515 The following functions are available on Perls built on VMS 7.2 or
518 fcntl (without locking)
520 The following functions may or may not be implemented,
521 depending on what type of socket support you've built into
524 accept, bind, connect, getpeername,
525 gethostbyname, getnetbyname, getprotobyname,
526 getservbyname, gethostbyaddr, getnetbyaddr,
527 getprotobynumber, getservbyport, gethostent,
528 getnetent, getprotoent, getservent, sethostent,
529 setnetent, setprotoent, setservent, endhostent,
530 endnetent, endprotoent, endservent, getsockname,
531 getsockopt, listen, recv, select(system call)*,
532 send, setsockopt, shutdown, socket
534 The following function is available on Perls built on 64 bit OpenVMS v8.2
535 with hard links enabled on an ODS-5 formatted build disk. CRTL support
536 is in principle available as of OpenVMS v7.3-1, and better configuration
537 support could detect this.
541 The following functions are available on Perls built on 64 bit OpenVMS
542 v8.2 and later. CRTL support is in principle available as of OpenVMS
543 v7.3-2, and better configuration support could detect this.
545 getgrgid, getgrnam, getpwnam, getpwuid,
548 The following functions are available on Perls built on 64 bit OpenVMS v8.2
557 The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
558 C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
559 advertised. The return values for C<-r>, C<-w>, and C<-x>
560 tell you whether you can actually access the file; this may
561 not reflect the UIC-based file protections. Since real and
562 effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
563 and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
564 Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
565 C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
566 VMS, and the values returned by these tests reflect whatever
567 your CRTL C<stat()> routine does to the equivalent bits in the
568 st_mode field. Finally, C<-d> returns true if passed a device
569 specification without an explicit directory (e.g. C<DUA1:>), as
570 well as if passed a directory.
572 There are DECC feature logical names AND ODS-5 volume attributes that
573 also control what values are returned for the date fields.
575 Note: Some sites have reported problems when using the file-access
576 tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
577 Specifically, since DFS does not currently provide access to the
578 extended file header of files on remote volumes, attempts to
579 examine the ACL fail, and the file tests will return false,
580 with C<$!> indicating that the file does not exist. You can
581 use C<stat> on these files, since that checks UIC-based protection
582 only, and then manually check the appropriate bits, as defined by
583 your C compiler's F<stat.h>, in the mode value it returns, if you
584 need an approximation of the file's protections.
588 Backticks create a subprocess, and pass the enclosed string
589 to it for execution as a DCL command. Since the subprocess is
590 created directly via C<lib$spawn()>, any valid DCL command string
593 =item binmode FILEHANDLE
595 The C<binmode> operator will attempt to insure that no translation
596 of carriage control occurs on input from or output to this filehandle.
597 Since this involves reopening the file and then restoring its
598 file position indicator, if this function returns FALSE, the
599 underlying filehandle may no longer point to an open file, or may
600 point to a different position in the file than before C<binmode>
603 Note that C<binmode> is generally not necessary when using normal
604 filehandles; it is provided so that you can control I/O to existing
605 record-structured files when necessary. You can also use the
606 C<vmsfopen> function in the VMS::Stdio extension to gain finer
607 control of I/O to files and devices with different record structures.
609 =item crypt PLAINTEXT, USER
611 The C<crypt> operator uses the C<sys$hash_password> system
612 service to generate the hashed representation of PLAINTEXT.
613 If USER is a valid username, the algorithm and salt values
614 are taken from that user's UAF record. If it is not, then
615 the preferred algorithm and a salt of 0 are used. The
616 quadword encrypted value is returned as an 8-character string.
618 The value returned by C<crypt> may be compared against
619 the encrypted password from the UAF returned by the C<getpw*>
620 functions, in order to authenticate users. If you're
621 going to do this, remember that the encrypted password in
622 the UAF was generated using uppercase username and
623 password strings; you'll have to upcase the arguments to
624 C<crypt> to insure that you'll get the proper value:
626 sub validate_passwd {
627 my($user,$passwd) = @_;
629 if ( !($pwdhash = (getpwnam($user))[1]) ||
630 $pwdhash ne crypt("\U$passwd","\U$name") ) {
631 intruder_alert($name);
639 C<die> will force the native VMS exit status to be an SS$_ABORT code
640 if neither of the $! or $? status values are ones that would cause
641 the native status to be interpreted as being what VMS classifies as
642 SEVERE_ERROR severity for DCL error handling.
644 When C<PERL_VMS_POSIX_EXIT> is active (see L</"$?"> below), the native VMS exit
645 status value will have either one of the C<$!> or C<$?> or C<$^E> or
646 the Unix value 255 encoded into it in a way that the effective original
647 value can be decoded by other programs written in C, including Perl
648 and the GNV package. As per the normal non-VMS behavior of C<die> if
649 either C<$!> or C<$?> are non-zero, one of those values will be
650 encoded into a native VMS status value. If both of the Unix status
651 values are 0, and the C<$^E> value is set one of ERROR or SEVERE_ERROR
652 severity, then the C<$^E> value will be used as the exit code as is.
653 If none of the above apply, the Unix value of 255 will be encoded into
654 a native VMS exit status value.
656 Please note a significant difference in the behavior of C<die> in
657 the C<PERL_VMS_POSIX_EXIT> mode is that it does not force a VMS
658 SEVERE_ERROR status on exit. The Unix exit values of 2 through
659 255 will be encoded in VMS status values with severity levels of
660 SUCCESS. The Unix exit value of 1 will be encoded in a VMS status
661 value with a severity level of ERROR. This is to be compatible with
662 how the VMS C library encodes these values.
664 The minimum severity level set by C<die> in C<PERL_VMS_POSIX_EXIT> mode
665 may be changed to be ERROR or higher in the future depending on the
666 results of testing and further review.
668 See L</"$?"> for a description of the encoding of the Unix value to
669 produce a native VMS status containing it.
673 Rather than causing Perl to abort and dump core, the C<dump>
674 operator invokes the VMS debugger. If you continue to
675 execute the Perl program under the debugger, control will
676 be transferred to the label specified as the argument to
677 C<dump>, or, if no label was specified, back to the
678 beginning of the program. All other state of the program
679 (I<e.g.> values of variables, open file handles) are not
680 affected by calling C<dump>.
684 A call to C<exec> will cause Perl to exit, and to invoke the command
685 given as an argument to C<exec> via C<lib$do_command>. If the
686 argument begins with '@' or '$' (other than as part of a filespec),
687 then it is executed as a DCL command. Otherwise, the first token on
688 the command line is treated as the filespec of an image to run, and
689 an attempt is made to invoke it (using F<.Exe> and the process
690 defaults to expand the filespec) and pass the rest of C<exec>'s
691 argument to it as parameters. If the token has no file type, and
692 matches a file with null type, then an attempt is made to determine
693 whether the file is an executable image which should be invoked
694 using C<MCR> or a text file which should be passed to DCL as a
699 While in principle the C<fork> operator could be implemented via
700 (and with the same rather severe limitations as) the CRTL C<vfork()>
701 routine, and while some internal support to do just that is in
702 place, the implementation has never been completed, making C<fork>
703 currently unavailable. A true kernel C<fork()> is expected in a
704 future version of VMS, and the pseudo-fork based on interpreter
705 threads may be available in a future version of Perl on VMS (see
706 L<perlfork>). In the meantime, use C<system>, backticks, or piped
707 filehandles to create subprocesses.
715 These operators obtain the information described in L<perlfunc>,
716 if you have the privileges necessary to retrieve the named user's
717 UAF information via C<sys$getuai>. If not, then only the C<$name>,
718 C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
719 the login directory in VMS syntax, while the C<$comment> item
720 contains the login directory in Unix syntax. The C<$gcos> item
721 contains the owner field from the UAF record. The C<$quota>
726 The C<gmtime> operator will function properly if you have a
727 working CRTL C<gmtime()> routine, or if the logical name
728 SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
729 which must be added to UTC to yield local time. (This logical
730 name is defined automatically if you are running a version of
731 VMS with built-in UTC support.) If neither of these cases is
732 true, a warning message is printed, and C<undef> is returned.
736 In most cases, C<kill> is implemented via the undocumented system
737 service C<$SIGPRC>, which has the same calling sequence as C<$FORCEX>, but
738 throws an exception in the target process rather than forcing it to call
739 C<$EXIT>. Generally speaking, C<kill> follows the behavior of the
740 CRTL's C<kill()> function, but unlike that function can be called from
741 within a signal handler. Also, unlike the C<kill> in some versions of
742 the CRTL, Perl's C<kill> checks the validity of the signal passed in and
743 returns an error rather than attempting to send an unrecognized signal.
745 Also, negative signal values don't do anything special under
746 VMS; they're just converted to the corresponding positive value.
750 See the entry on C<backticks> above.
752 =item select (system call)
754 If Perl was not built with socket support, the system call
755 version of C<select> is not available at all. If socket
756 support is present, then the system call version of
757 C<select> functions only for file descriptors attached
758 to sockets. It will not provide information about regular
759 files or pipes, since the CRTL C<select()> routine does not
760 provide this functionality.
764 Since VMS keeps track of files according to a different scheme
765 than Unix, it's not really possible to represent the file's ID
766 in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
767 tries its best, though, and the values it uses are pretty unlikely
768 to be the same for two different files. We can't guarantee this,
769 though, so caveat scriptor.
773 The C<system> operator creates a subprocess, and passes its
774 arguments to the subprocess for execution as a DCL command.
775 Since the subprocess is created directly via C<lib$spawn()>, any
776 valid DCL command string may be specified. If the string begins with
777 '@', it is treated as a DCL command unconditionally. Otherwise, if
778 the first token contains a character used as a delimiter in file
779 specification (e.g. C<:> or C<]>), an attempt is made to expand it
780 using a default type of F<.Exe> and the process defaults, and if
781 successful, the resulting file is invoked via C<MCR>. This allows you
782 to invoke an image directly simply by passing the file specification
783 to C<system>, a common Unixish idiom. If the token has no file type,
784 and matches a file with null type, then an attempt is made to
785 determine whether the file is an executable image which should be
786 invoked using C<MCR> or a text file which should be passed to DCL
787 as a command procedure.
789 If LIST consists of the empty string, C<system> spawns an
790 interactive DCL subprocess, in the same fashion as typing
791 B<SPAWN> at the DCL prompt.
793 Perl waits for the subprocess to complete before continuing
794 execution in the current process. As described in L<perlfunc>,
795 the return value of C<system> is a fake "status" which follows
796 POSIX semantics unless the pragma C<use vmsish 'status'> is in
797 effect; see the description of C<$?> in this document for more
802 The value returned by C<time> is the offset in seconds from
803 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
804 to make life easier for code coming in from the POSIX/Unix world.
808 The array returned by the C<times> operator is divided up
809 according to the same rules the CRTL C<times()> routine.
810 Therefore, the "system time" elements will always be 0, since
811 there is no difference between "user time" and "system" time
812 under VMS, and the time accumulated by a subprocess may or may
813 not appear separately in the "child time" field, depending on
814 whether C<times()> keeps track of subprocesses separately. Note
815 especially that the VAXCRTL (at least) keeps track only of
816 subprocesses spawned using C<fork()> and C<exec()>; it will not
817 accumulate the times of subprocesses spawned via pipes, C<system()>,
822 C<unlink> will delete the highest version of a file only; in
823 order to delete all versions, you need to say
827 You may need to make this change to scripts written for a
828 Unix system which expect that after a call to C<unlink>,
829 no files with the names passed to C<unlink> will exist.
830 (Note: This can be changed at compile time; if you
831 C<use Config> and C<$Config{'d_unlink_all_versions'}> is
832 C<define>, then C<unlink> will delete all versions of a
833 file on the first call.)
835 C<unlink> will delete a file if at all possible, even if it
836 requires changing file protection (though it won't try to
837 change the protection of the parent directory). You can tell
838 whether you've got explicit delete access to a file by using the
839 C<VMS::Filespec::candelete> operator. For instance, in order
840 to delete only files to which you have delete access, you could
846 next unless VMS::Filespec::candelete($file);
847 $num += unlink $file;
852 (or you could just use C<VMS::Stdio::remove>, if you've installed
853 the VMS::Stdio extension distributed with Perl). If C<unlink> has to
854 change the file protection to delete the file, and you interrupt it
855 in midstream, the file may be left intact, but with a changed ACL
856 allowing you delete access.
858 This behavior of C<unlink> is to be compatible with POSIX behavior
859 and not traditional VMS behavior.
863 This operator changes only the modification time of the file (VMS
864 revision date) on ODS-2 volumes and ODS-5 volumes without access
865 dates enabled. On ODS-5 volumes with access dates enabled, the
866 true access time is modified.
868 =item waitpid PID,FLAGS
870 If PID is a subprocess started by a piped C<open()> (see L<open>),
871 C<waitpid> will wait for that subprocess, and return its final status
872 value in C<$?>. If PID is a subprocess created in some other way (e.g.
873 SPAWNed before Perl was invoked), C<waitpid> will simply check once per
874 second whether the process has completed, and return when it has. (If
875 PID specifies a process that isn't a subprocess of the current process,
876 and you invoked Perl with the C<-w> switch, a warning will be issued.)
878 Returns PID on success, -1 on error. The FLAGS argument is ignored
883 =head1 Perl variables
885 The following VMS-specific information applies to the indicated
886 "special" Perl variables, in addition to the general information
887 in L<perlvar>. Where there is a conflict, this information
894 The operation of the C<%ENV> array depends on the translation
895 of the logical name F<PERL_ENV_TABLES>. If defined, it should
896 be a search list, each element of which specifies a location
897 for C<%ENV> elements. If you tell Perl to read or set the
898 element C<$ENV{>I<name>C<}>, then Perl uses the translations of
899 F<PERL_ENV_TABLES> as follows:
905 This string tells Perl to consult the CRTL's internal C<environ> array
906 of key-value pairs, using I<name> as the key. In most cases, this
907 contains only a few keys, but if Perl was invoked via the C
908 C<exec[lv]e()> function, as is the case for some embedded Perl
909 applications or when running under a shell such as GNV bash, the
910 C<environ> array may have been populated by the calling program.
914 A string beginning with C<CLISYM_>tells Perl to consult the CLI's
915 symbol tables, using I<name> as the name of the symbol. When reading
916 an element of C<%ENV>, the local symbol table is scanned first, followed
917 by the global symbol table.. The characters following C<CLISYM_> are
918 significant when an element of C<%ENV> is set or deleted: if the
919 complete string is C<CLISYM_LOCAL>, the change is made in the local
920 symbol table; otherwise the global symbol table is changed.
922 =item Any other string
924 If an element of F<PERL_ENV_TABLES> translates to any other string,
925 that string is used as the name of a logical name table, which is
926 consulted using I<name> as the logical name. The normal search
927 order of access modes is used.
931 F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
932 you make while Perl is running do not affect the behavior of C<%ENV>.
933 If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
934 first the logical name tables specified by F<LNM$FILE_DEV>, and then
935 the CRTL C<environ> array. This default order is reversed when the
936 logical name F<GNV$UNIX_SHELL> is defined, such as when running under
939 For operations on %ENV entries based on logical names or DCL symbols, the
940 key string is treated as if it were entirely uppercase, regardless of the
941 case actually specified in the Perl expression. Entries in %ENV based on the
942 CRTL's environ array preserve the case of the key string when stored, and
943 lookups are case sensitive.
945 When an element of C<%ENV> is read, the locations to which
946 F<PERL_ENV_TABLES> points are checked in order, and the value
947 obtained from the first successful lookup is returned. If the
948 name of the C<%ENV> element contains a semi-colon, it and
949 any characters after it are removed. These are ignored when
950 the CRTL C<environ> array or a CLI symbol table is consulted.
951 However, the name is looked up in a logical name table, the
952 suffix after the semi-colon is treated as the translation index
953 to be used for the lookup. This lets you look up successive values
954 for search list logical names. For instance, if you say
956 $ Define STORY once,upon,a,time,there,was
957 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
958 _$ -e "{ print $ENV{'story;'.$i},' '}"
960 Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
961 that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
962 is found, rather than a CLI symbol or CRTL C<environ> element with
965 When an element of C<%ENV> is set to a defined string, the
966 corresponding definition is made in the location to which the
967 first translation of F<PERL_ENV_TABLES> points. If this causes a
968 logical name to be created, it is defined in supervisor mode.
969 (The same is done if an existing logical name was defined in
970 executive or kernel mode; an existing user or supervisor mode
971 logical name is reset to the new value.) If the value is an empty
972 string, the logical name's translation is defined as a single C<NUL>
973 (ASCII C<\0>) character, since a logical name cannot translate to a
974 zero-length string. (This restriction does not apply to CLI symbols
975 or CRTL C<environ> values; they are set to the empty string.)
977 When an element of C<%ENV> is set to C<undef>, the element is looked
978 up as if it were being read, and if it is found, it is deleted. (An
979 item "deleted" from the CRTL C<environ> array is set to the empty
980 string.) Using C<delete> to remove an element from C<%ENV> has a
981 similar effect, but after the element is deleted, another attempt is
982 made to look up the element, so an inner-mode logical name or a name
983 in another location will replace the logical name just deleted. In
984 either case, only the first value found searching PERL_ENV_TABLES is
985 altered. It is not possible at present to define a search list
986 logical name via %ENV.
988 The element C<$ENV{DEFAULT}> is special: when read, it returns
989 Perl's current default device and directory, and when set, it
990 resets them, regardless of the definition of F<PERL_ENV_TABLES>.
991 It cannot be cleared or deleted; attempts to do so are silently
994 Note that if you want to pass on any elements of the
995 C-local environ array to a subprocess which isn't
996 started by fork/exec, or isn't running a C program, you
997 can "promote" them to logical names in the current
998 process, which will then be inherited by all subprocesses,
1001 foreach my $key (qw[C-local keys you want promoted]) {
1002 my $temp = $ENV{$key}; # read from C-local array
1003 $ENV{$key} = $temp; # and define as logical name
1006 (You can't just say C<$ENV{$key} = $ENV{$key}>, since the
1007 Perl optimizer is smart enough to elide the expression.)
1009 Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
1010 a fatal error. This is equivalent to doing the following from DCL:
1014 You can imagine how bad things would be if, for example, the SYS$MANAGER
1015 or SYS$SYSTEM logical names were deleted.
1017 At present, the first time you iterate over %ENV using
1018 C<keys>, or C<values>, you will incur a time penalty as all
1019 logical names are read, in order to fully populate %ENV.
1020 Subsequent iterations will not reread logical names, so they
1021 won't be as slow, but they also won't reflect any changes
1022 to logical name tables caused by other programs.
1024 You do need to be careful with the logical names representing
1025 process-permanent files, such as C<SYS$INPUT> and C<SYS$OUTPUT>.
1026 The translations for these logical names are prepended with a
1027 two-byte binary value (0x1B 0x00) that needs to be stripped off
1028 if you want to use it. (In previous versions of Perl it wasn't
1029 possible to get the values of these logical names, as the null
1030 byte acted as an end-of-string marker)
1034 The string value of C<$!> is that returned by the CRTL's
1035 strerror() function, so it will include the VMS message for
1036 VMS-specific errors. The numeric value of C<$!> is the
1037 value of C<errno>, except if errno is EVMSERR, in which
1038 case C<$!> contains the value of vaxc$errno. Setting C<$!>
1039 always sets errno to the value specified. If this value is
1040 EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
1041 that the string value of C<$!> won't reflect the VMS error
1042 message from before C<$!> was set.
1046 This variable provides direct access to VMS status values
1047 in vaxc$errno, which are often more specific than the
1048 generic Unix-style error messages in C<$!>. Its numeric value
1049 is the value of vaxc$errno, and its string value is the
1050 corresponding VMS message string, as retrieved by sys$getmsg().
1051 Setting C<$^E> sets vaxc$errno to the value specified.
1053 While Perl attempts to keep the vaxc$errno value to be current, if
1054 errno is not EVMSERR, it may not be from the current operation.
1058 The "status value" returned in C<$?> is synthesized from the
1059 actual exit status of the subprocess in a way that approximates
1060 POSIX wait(5) semantics, in order to allow Perl programs to
1061 portably test for successful completion of subprocesses. The
1062 low order 8 bits of C<$?> are always 0 under VMS, since the
1063 termination status of a process may or may not have been
1064 generated by an exception.
1066 The next 8 bits contain the termination status of the program.
1068 If the child process follows the convention of C programs
1069 compiled with the _POSIX_EXIT macro set, the status value will
1070 contain the actual value of 0 to 255 returned by that program
1073 With the _POSIX_EXIT macro set, the Unix exit value of zero is
1074 represented as a VMS native status of 1, and the Unix values
1075 from 2 to 255 are encoded by the equation:
1077 VMS_status = 0x35a000 + (unix_value * 8) + 1.
1079 And in the special case of Unix value 1 the encoding is:
1081 VMS_status = 0x35a000 + 8 + 2 + 0x10000000.
1083 For other termination statuses, the severity portion of the
1084 subprocess's exit status is used: if the severity was success or
1085 informational, these bits are all 0; if the severity was
1086 warning, they contain a value of 1; if the severity was
1087 error or fatal error, they contain the actual severity bits,
1088 which turns out to be a value of 2 for error and 4 for severe_error.
1089 Fatal is another term for the severe_error status.
1091 As a result, C<$?> will always be zero if the subprocess's exit
1092 status indicated successful completion, and non-zero if a
1093 warning or error occurred or a program compliant with encoding
1094 _POSIX_EXIT values was run and set a status.
1096 How can you tell the difference between a non-zero status that is
1097 the result of a VMS native error status or an encoded Unix status?
1098 You can not unless you look at the ${^CHILD_ERROR_NATIVE} value.
1099 The ${^CHILD_ERROR_NATIVE} value returns the actual VMS status value
1100 and check the severity bits. If the severity bits are equal to 1,
1101 then if the numeric value for C<$?> is between 2 and 255 or 0, then
1102 C<$?> accurately reflects a value passed back from a Unix application.
1103 If C<$?> is 1, and the severity bits indicate a VMS error (2), then
1104 C<$?> is from a Unix application exit value.
1106 In practice, Perl scripts that call programs that return _POSIX_EXIT
1107 type status values will be expecting those values, and programs that
1108 call traditional VMS programs will either be expecting the previous
1109 behavior or just checking for a non-zero status.
1111 And success is always the value 0 in all behaviors.
1113 When the actual VMS termination status of the child is an error,
1114 internally the C<$!> value will be set to the closest Unix errno
1115 value to that error so that Perl scripts that test for error
1116 messages will see the expected Unix style error message instead
1119 Conversely, when setting C<$?> in an END block, an attempt is made
1120 to convert the POSIX value into a native status intelligible to
1121 the operating system upon exiting Perl. What this boils down to
1122 is that setting C<$?> to zero results in the generic success value
1123 SS$_NORMAL, and setting C<$?> to a non-zero value results in the
1124 generic failure status SS$_ABORT. See also L<perlport/exit>.
1126 With the C<PERL_VMS_POSIX_EXIT> logical name defined as "ENABLE",
1127 setting C<$?> will cause the new value to be encoded into C<$^E>
1128 so that either the original parent or child exit status values
1129 0 to 255 can be automatically recovered by C programs expecting
1130 _POSIX_EXIT behavior. If both a parent and a child exit value are
1131 non-zero, then it will be assumed that this is actually a VMS native
1132 status value to be passed through. The special value of 0xFFFF is
1133 almost a NOOP as it will cause the current native VMS status in the
1134 C library to become the current native Perl VMS status, and is handled
1135 this way as it is known to not be a valid native VMS status value.
1136 It is recommend that only values in the range of normal Unix parent or
1137 child status numbers, 0 to 255 are used.
1139 The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
1140 VMS exit status instead of the default emulation of POSIX status
1141 described above. This pragma also disables the conversion of
1142 non-zero values to SS$_ABORT when setting C<$?> in an END
1143 block (but zero will still be converted to SS$_NORMAL).
1145 Do not use the pragma C<use vmsish 'status'> with C<PERL_VMS_POSIX_EXIT>
1146 enabled, as they are at times requesting conflicting actions and the
1147 consequence of ignoring this advice will be undefined to allow future
1148 improvements in the POSIX exit handling.
1150 In general, with C<PERL_VMS_POSIX_EXIT> enabled, more detailed information
1151 will be available in the exit status for DCL scripts or other native VMS tools,
1152 and will give the expected information for Posix programs. It has not been
1153 made the default in order to preserve backward compatibility.
1155 N.B. Setting C<DECC$FILENAME_UNIX_REPORT> implicitly enables
1156 C<PERL_VMS_POSIX_EXIT>.
1160 Setting C<$|> for an I/O stream causes data to be flushed
1161 all the way to disk on each write (I<i.e.> not just to
1162 the underlying RMS buffers for a file). In other words,
1163 it's equivalent to calling fflush() and fsync() from C.
1167 =head1 Standard modules with VMS-specific differences
1171 SDBM_File works properly on VMS. It has, however, one minor
1172 difference. The database directory file created has a F<.sdbm_dir>
1173 extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
1174 directory files, and using them for other purposes could cause unacceptable
1177 =head1 Revision date
1179 Please see the git repository for revision history.
1183 Charles Bailey bailey@cor.newman.upenn.edu
1184 Craig Berry craigberry@mac.com
1185 Dan Sugalski dan@sidhe.org
1186 John Malmberg wb8tyw@qsl.net