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e518068a 1=head1 NAME
3perlvms - VMS-specific documentation for Perl
a0d0e21e 6
7Gathered below are notes describing details of Perl 5's
8behavior on VMS. They are a supplement to the regular Perl 5
9documentation, so we have focussed on the ways in which Perl
105 functions differently under VMS than it does under Unix,
11and on the interactions between Perl and the rest of the
a0d0e21e 12operating system. We haven't tried to duplicate complete
748a9306 13descriptions of Perl features from the main Perl
a0d0e21e 14documentation, which can be found in the F<[.pod]>
748a9306 15subdirectory of the Perl distribution.
17We hope these notes will save you from confusion and lost
748a9306 18sleep when writing Perl scripts on VMS. If you find we've
19missed something you think should appear here, please don't
20hesitate to drop a line to
4e592037 22=head1 Installation
24Directions for building and installing Perl 5 can be found in
25the file F<README.vms> in the main source directory of the
26Perl distribution..
e518068a 28=head1 Organization of Perl Images
748a9306 29
e518068a 30=head2 Core Images
32During the installation process, three Perl images are produced.
33F<Miniperl.Exe> is an executable image which contains all of
34the basic functionality of Perl, but cannot take advantage of
35Perl extensions. It is used to generate several files needed
36to build the complete Perl and various extensions. Once you've
37finished installing Perl, you can delete this image.
39Most of the complete Perl resides in the shareable image
40F<PerlShr.Exe>, which provides a core to which the Perl executable
41image and all Perl extensions are linked. You should place this
42image in F<Sys$Share>, or define the logical name F<PerlShr> to
43translate to the full file specification of this image. It should
44be world readable. (Remember that if a user has execute only access
45to F<PerlShr>, VMS will treat it as if it were a privileged shareable
46image, and will therefore require all downstream shareable images to be
47INSTALLed, etc.)
50Finally, F<Perl.Exe> is an executable image containing the main
51entry point for Perl, as well as some initialization code. It
52should be placed in a public directory, and made world executable.
53In order to run Perl with command line arguments, you should
54define a foreign command to invoke this image.
56=head2 Perl Extensions
58Perl extensions are packages which provide both XS and Perl code
59to add new functionality to perl. (XS is a meta-language which
60simplifies writing C code which interacts with Perl, see
2ceaccd7 61L<perlxs> for more details.) The Perl code for an
62extension is treated like any other library module - it's
63made available in your script through the appropriate
64C<use> or C<require> statement, and usually defines a Perl
65package containing the extension.
67The portion of the extension provided by the XS code may be
68connected to the rest of Perl in either of two ways. In the
69B<static> configuration, the object code for the extension is
70linked directly into F<PerlShr.Exe>, and is initialized whenever
71Perl is invoked. In the B<dynamic> configuration, the extension's
72machine code is placed into a separate shareable image, which is
73mapped by Perl's DynaLoader when the extension is C<use>d or
74C<require>d in your script. This allows you to maintain the
75extension as a separate entity, at the cost of keeping track of the
76additional shareable image. Most extensions can be set up as either
77static or dynamic.
79The source code for an extension usually resides in its own
80directory. At least three files are generally provided:
81I<Extshortname>F<.xs> (where I<Extshortname> is the portion of
82the extension's name following the last C<::>), containing
83the XS code, I<Extshortname>F<.pm>, the Perl library module
84for the extension, and F<Makefile.PL>, a Perl script which uses
85the C<MakeMaker> library modules supplied with Perl to generate
86a F<Descrip.MMS> file for the extension.
e518068a 88=head2 Installing static extensions
90Since static extensions are incorporated directly into
91F<PerlShr.Exe>, you'll have to rebuild Perl to incorporate a
92new extension. You should edit the main F<Descrip.MMS> or F<Makefile>
93you use to build Perl, adding the extension's name to the C<ext>
94macro, and the extension's object file to the C<extobj> macro.
95You'll also need to build the extension's object file, either
96by adding dependencies to the main F<Descrip.MMS>, or using a
97separate F<Descrip.MMS> for the extension. Then, rebuild
98F<PerlShr.Exe> to incorporate the new code.
100Finally, you'll need to copy the extension's Perl library
101module to the F<[.>I<Extname>F<]> subdirectory under one
102of the directories in C<@INC>, where I<Extname> is the name
103of the extension, with all C<::> replaced by C<.> (e.g.
104the library module for extension Foo::Bar would be copied
105to a F<[.Foo.Bar]> subdirectory).
e518068a 107=head2 Installing dynamic extensions
109In general, the distributed kit for a Perl extension includes
110a file named Makefile.PL, which is a Perl program which is used
111to create a F<Descrip.MMS> file which can be used to build and
112install the files required by the extension. The kit should be
c07a80fd 113unpacked into a directory tree B<not> under the main Perl source
e518068a 114directory, and the procedure for building the extension is simply
e518068a 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
c07a80fd 121I<N.B.> The procedure by which extensions are built and
122tested creates several levels (at least 4) under the
123directory in which the extension's source files live.
124For this reason, you shouldn't nest the source directory
125too deeply in your directory structure, lest you eccedd RMS'
126maximum of 8 levels of subdirectory in a filespec. (You
127can use rooted logical names to get another 8 levels of
128nesting, if you can't place the files near the top of
129the physical directory structure.)
e518068a 130
131VMS support for this process in the current release of Perl
132is sufficient to handle most extensions. However, it does
133not yet recognize extra libraries required to build shareable
134images which are part of an extension, so these must be added
135to the linker options file for the extension by hand. For
136instance, if the F<PGPLOT> extension to Perl requires the
137F<PGPLOTSHR.EXE> shareable image in order to properly link
138the Perl extension, then the line C<PGPLOTSHR/Share> must
139be added to the linker options file F<PGPLOT.Opt> produced
140during the build process for the Perl extension.
142By default, the shareable image for an extension is placed
bbce6d69 143F<[>I<Arch>.I<Extname>F<]> directory of the
e518068a 144installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
bbce6d69 145F<VMS_AXP>, and I<Extname> is the name of the extension, with
146each C<::> translated to C<.>). (See the MakeMaker documentation
147for more details on installation options for extensions.)
4e592037 148However, it can be manually placed in any of several locations:
bbce6d69 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>.
158If the shareable image isn't in any of these places, you'll need
159to define a logical name I<Extshortname>, where I<Extshortname>
160is the portion of the extension's name after the last C<::>, which
161translates to the full file specification of the shareable image.
4e592037 163=head1 File specifications
748a9306 164
4e592037 165=head2 Syntax
a0d0e21e 166
748a9306 167We have tried to make Perl aware of both VMS-style and Unix-
168style file specifications wherever possible. You may use
169either style, or both, on the command line and in scripts,
170but you may not combine the two styles within a single fle
1c9f8daa 171specification. VMS Perl interprets Unix pathnames in much
172the same way as the CRTL (I<e.g.> the first component of
173an absolute path is read as the device name for the
174VMS file specification). There are a set of functions
175provided in the C<VMS::Filespec> package for explicit
176interconversion between VMS and Unix syntax; its
177documentation provides more details.
179Filenames are, of course, still case-insensitive. For
180consistency, most Perl routines return filespecs using
181lower case letters only, regardless of the case used in
182the arguments passed to them. (This is true only when
183running under VMS; Perl respects the case-sensitivity
184of OSs like Unix.)
a0d0e21e 185
748a9306 186We've tried to minimize the dependence of Perl library
187modules on Unix syntax, but you may find that some of these,
188as well as some scripts written for Unix systems, will
189require that you use Unix syntax, since they will assume that
4e592037 190'/' is the directory separator, I<etc.> If you find instances
748a9306 191of this in the Perl distribution itself, please let us know,
192so we can try to work around them.
4e592037 194=head2 Wildcard expansion
196File specifications containing wildcards are allowed both on
197the command line and within Perl globs (e.g. <CE<lt>*.cE<gt>>). If
198the wildcard filespec uses VMS syntax, the resultant
199filespecs will follow VMS syntax; if a Unix-style filespec is
200passed in, Unix-style filespecs will be returned.
202If the wildcard filespec contains a device or directory
203specification, then the resultant filespecs will also contain
204a device and directory; otherwise, device and directory
205information are removed. VMS-style resultant filespecs will
206contain a full device and directory, while Unix-style
207resultant filespecs will contain only as much of a directory
208path as was present in the input filespec. For example, if
209your default directory is Perl_Root:[000000], the expansion
210of C<[.t]*.*> will yield filespecs like
211"perl_root:[t]base.dir", while the expansion of C<t/*/*> will
212yield filespecs like "t/base.dir". (This is done to match
213the behavior of glob expansion performed by Unix shells.)
215Similarly, the resultant filespec will contain the file version
216only if one was present in the input filespec.
218=head2 Pipes
220Input and output pipes to Perl filehandles are supported; the
221"file name" is passed to lib$spawn() for asynchronous
222execution. You should be careful to close any pipes you have
223opened in a Perl script, lest you leave any "orphaned"
224subprocesses around when Perl exits.
226You may also use backticks to invoke a DCL subprocess, whose
227output is used as the return value of the expression. The
228string between the backticks is passed directly to lib$spawn
229as the command to execute. In this case, Perl will wait for
230the subprocess to complete before continuing.
232=head1 PERL5LIB and PERLLIB
234The PERL5LIB and PERLLIB logical names work as documented L<perl>,
235except that the element separator is '|' instead of ':'. The
236directory specifications may use either VMS or Unix syntax.
238=head1 Command line
240=head2 I/O redirection and backgrounding
242Perl for VMS supports redirection of input and output on the
243command line, using a subset of Bourne shell syntax:
55497cff 244
245 <F<file> reads stdin from F<file>,
246 >F<file> writes stdout to F<file>,
247 >>F<file> appends stdout to F<file>,
748a9306 248 2>F<file> writes stderr to F<file>, and
249 2>>F<file> appends stderr to F<file>.
251In addition, output may be piped to a subprocess, using the
252character '|'. Anything after this character on the command
253line is passed to a subprocess for execution; the subprocess
748a9306 254takes the output of Perl as its input.
256Finally, if the command line ends with '&', the entire
257command is run in the background as an asynchronous
4e592037 260=head2 Command line switches
a0d0e21e 261
4e592037 262The following command line switches behave differently under
263VMS than described in L<perlrun>. Note also that in order
264to pass uppercase switches to Perl, you need to enclose
265them in double-quotes on the command line, since the CRTL
266downcases all unquoted strings.
a0d0e21e 267
55497cff 268=over 4
270=item -i
272If the C<-i> switch is present but no extension for a backup
273copy is given, then inplace editing creates a new version of
274a file; the existing copy is not deleted. (Note that if
275an extension is given, an existing file is renamed to the backup
276file, as is the case under other operating systems, so it does
277not remain as a previous version under the original filename.)
4e592037 279=item -S
a0d0e21e 280
4e592037 281If the C<-S> switch is present I<and> the script name does
282not contain a directory, then Perl translates the logical
283name DCL$PATH as a searchlist, using each translation as
284a directory in which to look for the script. In addition,
285if no file type is specified, Perl looks in each directory
286for a file matching the name specified, with a blank type,
287a type of F<.pl>, and a type of F<.com>, in that order.
a0d0e21e 288
4e592037 289=item -u
748a9306 290
4e592037 291The C<-u> switch causes the VMS debugger to be invoked
292after the Perl program is compiled, but before it has
293run. It does not create a core dump file.
748a9306 294
55497cff 295=back
748a9306 297=head1 Perl functions
299As of the time this document was last revised, the following
748a9306 300Perl functions were implemented in the VMS port of Perl
301(functions marked with * are discussed in more detail below):
4fdae800 303 file tests*, abs, alarm, atan, backticks*, binmode*, bless,
a0d0e21e 304 caller, chdir, chmod, chown, chomp, chop, chr,
c07a80fd 305 close, closedir, cos, crypt*, defined, delete,
4e592037 306 die, do, dump*, each, endpwent, eof, eval, exec*,
307 exists, exit, exp, fileno, fork*, getc, getlogin,
308 getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
309 grep, hex, import, index, int, join, keys, kill*,
310 last, lc, lcfirst, length, local, localtime, log, m//,
311 map, mkdir, my, next, no, oct, open, opendir, ord, pack,
c07a80fd 312 pipe, pop, pos, print, printf, push, q//, qq//, qw//,
4fdae800 313 qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
a0d0e21e 314 require, reset, return, reverse, rewinddir, rindex,
e518068a 315 rmdir, s///, scalar, seek, seekdir, select(internal),
316 select (system call)*, setpwent, shift, sin, sleep,
317 sort, splice, split, sprintf, sqrt, srand, stat,
318 study, substr, sysread, system*, syswrite, tell,
319 telldir, tie, time, times*, tr///, uc, ucfirst, umask,
320 undef, unlink*, unpack, untie, unshift, use, utime*,
321 values, vec, wait, waitpid*, wantarray, warn, write, y///
323The following functions were not implemented in the VMS port,
324and calling them produces a fatal error (usually) or
325undefined behavior (rarely, we hope):
4e592037 327 chroot, dbmclose, dbmopen, fcntl, flock,
c07a80fd 328 getpgrp, getppid, getpriority, getgrent, getgrgid,
329 getgrnam, setgrent, endgrent, ioctl, link, lstat,
330 msgctl, msgget, msgsend, msgrcv, readlink, semctl,
331 semget, semop, setpgrp, setpriority, shmctl, shmget,
332 shmread, shmwrite, socketpair, symlink, syscall
334The following functions are available on Perls compiled with Dec C 5.2 or
335greater and running VMS 7.0 or greater
337 truncate
339The following functions may or may not be implemented,
340depending on what type of socket support you've built into
748a9306 341your copy of Perl:
4e592037 342
343 accept, bind, connect, getpeername,
344 gethostbyname, getnetbyname, getprotobyname,
345 getservbyname, gethostbyaddr, getnetbyaddr,
346 getprotobynumber, getservbyport, gethostent,
347 getnetent, getprotoent, getservent, sethostent,
348 setnetent, setprotoent, setservent, endhostent,
349 endnetent, endprotoent, endservent, getsockname,
c07a80fd 350 getsockopt, listen, recv, select(system call)*,
351 send, setsockopt, shutdown, socket
a0d0e21e 352
55497cff 353=over 4
355=item File tests
357The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
358C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
359advertised. The return values for C<-r>, C<-w>, and C<-x>
360tell you whether you can actually access the file; this may
361not reflect the UIC-based file protections. Since real and
362effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
363and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
364Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
365C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
366VMS, and the values returned by these tests reflect whatever
367your CRTL C<stat()> routine does to the equivalent bits in the
368st_mode field. Finally, C<-d> returns true if passed a device
369specification without an explicit directory (e.g. C<DUA1:>), as
370well as if passed a directory.
4e592037 372Note: Some sites have reported problems when using the file-access
373tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
374Specifically, since DFS does not currently provide access to the
375extended file header of files on remote volumes, attempts to
376examine the ACL fail, and the file tests will return false,
377with C<$!> indicating that the file does not exist. You can
378use C<stat> on these files, since that checks UIC-based protection
379only, and then manually check the appropriate bits, as defined by
380your C compiler's F<stat.h>, in the mode value it returns, if you
381need an approximation of the file's protections.
4fdae800 383=item backticks
385Backticks create a subprocess, and pass the enclosed string
386to it for execution as a DCL command. Since the subprocess is
387created directly via C<lib$spawn()>, any valid DCL command string
388may be specified.
390=item binmode FILEHANDLE
1c9f8daa 392The C<binmode> operator will attempt to insure that no translation
393of carriage control occurs on input from or output to this filehandle.
394Since this involves reopening the file and then restoring its
395file position indicator, if this function returns FALSE, the
396underlying filehandle may no longer point to an open file, or may
397point to a different position in the file than before C<binmode>
398was called.
400Note that C<binmode> is generally not necessary when using normal
401filehandles; it is provided so that you can control I/O to existing
402record-structured files when necessary. You can also use the
403C<vmsfopen> function in the VMS::Stdio extension to gain finer
404control of I/O to files and devices with different record structures.
a0d0e21e 405
c07a80fd 406=item crypt PLAINTEXT, USER
408The C<crypt> operator uses the C<sys$hash_password> system
409service to generate the hashed representation of PLAINTEXT.
410If USER is a valid username, the algorithm and salt values
411are taken from that user's UAF record. If it is not, then
412the preferred algorithm and a salt of 0 are used. The
413quadword encrypted value is returned as an 8-character string.
415The value returned by C<crypt> may be compared against
416the encrypted password from the UAF returned by the C<getpw*>
417functions, in order to authenticate users. If you're
418going to do this, remember that the encrypted password in
419the UAF was generated using uppercase username and
420password strings; you'll have to upcase the arguments to
421C<crypt> to insure that you'll get the proper value:
423 sub validate_passwd {
424 my($user,$passwd) = @_;
425 my($pwdhash);
426 if ( !($pwdhash = (getpwnam($user))[1]) ||
427 $pwdhash ne crypt("\U$passwd","\U$name") ) {
428 intruder_alert($name);
429 }
430 return 1;
431 }
4e592037 433=item dump
435Rather than causing Perl to abort and dump core, the C<dump>
436operator invokes the VMS debugger. If you continue to
437execute the Perl program under the debugger, control will
438be transferred to the label specified as the argument to
439C<dump>, or, if no label was specified, back to the
440beginning of the program. All other state of the program
441(I<e.g.> values of variables, open file handles) are not
442affected by calling C<dump>.
748a9306 444=item exec LIST
a0d0e21e 445
446The C<exec> operator behaves in one of two different ways.
447If called after a call to C<fork>, it will invoke the CRTL
448C<execv()> routine, passing its arguments to the subprocess
449created by C<fork> for execution. In this case, it is
450subject to all limitations that affect C<execv()>. (In
451particular, this usually means that the command executed in
452the subprocess must be an image compiled from C source code,
453and that your options for passing file descriptors and signal
454handlers to the subprocess are limited.)
456If the call to C<exec> does not follow a call to C<fork>, it
457will cause Perl to exit, and to invoke the command given as
458an argument to C<exec> via C<lib$do_command>. If the argument
459begins with a '$' (other than as part of a filespec), then it
460is executed as a DCL command. Otherwise, the first token on
461the command line is treated as the filespec of an image to
462run, and an attempt is made to invoke it (using F<.Exe> and
463the process defaults to expand the filespec) and pass the
748a9306 464rest of C<exec>'s argument to it as parameters.
a0d0e21e 465
466You can use C<exec> in both ways within the same script, as
467long as you call C<fork> and C<exec> in pairs. Perl
468keeps track of how many times C<fork> and C<exec> have been
469called, and will call the CRTL C<execv()> routine if there have
470previously been more calls to C<fork> than to C<exec>.
472=item fork
474The C<fork> operator works in the same way as the CRTL
475C<vfork()> routine, which is quite different under VMS than
476under Unix. Specifically, while C<fork> returns 0 after it
477is called and the subprocess PID after C<exec> is called, in
478both cases the thread of execution is within the parent
479process, so there is no opportunity to perform operations in
748a9306 480the subprocess before calling C<exec>.
a0d0e21e 481
748a9306 482In general, the use of C<fork> and C<exec> to create
a0d0e21e 483subprocess is not recommended under VMS; wherever possible,
484use the C<system> operator or piped filehandles instead.
486=item getpwent
c07a80fd 487
748a9306 488=item getpwnam
c07a80fd 489
490=item getpwuid
492These operators obtain the information described in L<perlfunc>,
493if you have the privileges necessary to retrieve the named user's
494UAF information via C<sys$getuai>. If not, then only the C<$name>,
495C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
496the login directory in VMS syntax, while the C<$comment> item
497contains the login directory in Unix syntax. The C<$gcos> item
498contains the owner field from the UAF record. The C<$quota>
499item is not used.
a0d0e21e 500
e518068a 501=item gmtime
503The C<gmtime> operator will function properly if you have a
504working CRTL C<gmtime()> routine, or if the logical name
505SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
506which must be added to UTC to yield local time. (This logical
507name is defined automatically if you are running a version of
508VMS with built-in UTC support.) If neither of these cases is
509true, a warning message is printed, and C<undef> is returned.
511=item kill
513In most cases, C<kill> kill is implemented via the CRTL's C<kill()>
514function, so it will behave according to that function's
515documentation. If you send a SIGKILL, however, the $DELPRC system
10a676f8 516service is called directly. This insures that the target
e518068a 517process is actually deleted, if at all possible. (The CRTL's C<kill()>
518function is presently implemented via $FORCEX, which is ignored by
519supervisor-mode images like DCL.)
521Also, negative signal values don't do anything special under
522VMS; they're just converted to the corresponding positive value.
4fdae800 524=item qx//
526See the entry on C<backticks> above.
e518068a 528=item select (system call)
530If Perl was not built with socket support, the system call
531version of C<select> is not available at all. If socket
532support is present, then the system call version of
533C<select> functions only for file descriptors attached
534to sockets. It will not provide information about regular
535files or pipes, since the CRTL C<select()> routine does not
536provide this functionality.
748a9306 538=item stat EXPR
a0d0e21e 539
540Since VMS keeps track of files according to a different scheme
541than Unix, it's not really possible to represent the file's ID
542in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
543tries its best, though, and the values it uses are pretty unlikely
544to be the same for two different files. We can't guarantee this,
545though, so caveat scriptor.
547=item system LIST
549The C<system> operator creates a subprocess, and passes its
a0d0e21e 550arguments to the subprocess for execution as a DCL command.
e518068a 551Since the subprocess is created directly via C<lib$spawn()>, any
552valid DCL command string may be specified. If LIST consists
553of the empty string, C<system> spawns an interactive DCL subprocess,
554in the same fashion as typiing B<SPAWN> at the DCL prompt.
555Perl waits for the subprocess to complete before continuing
4fdae800 556execution in the current process. As described in L<perlfunc>,
557the return value of C<system> is a fake "status" which follows
558POSIX semantics; see the description of C<$?> in this document
559for more detail. The actual VMS exit status of the subprocess
560is available in C<$^S> (as long as you haven't used another Perl
561function that resets C<$?> and C<$^S> in the meantime).
a0d0e21e 562
1c9f8daa 563=item time
565The value returned by C<time> is the offset in seconds from
56601-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
567to make life easier for code coming in from the POSIX/Unix world.
569=item times
571The array returned by the C<times> operator is divided up
572according to the same rules the CRTL C<times()> routine.
573Therefore, the "system time" elements will always be 0, since
574there is no difference between "user time" and "system" time
575under VMS, and the time accumulated by subprocess may or may
576not appear separately in the "child time" field, depending on
577whether L<times> keeps track of subprocesses separately. Note
578especially that the VAXCRTL (at least) keeps track only of
579subprocesses spawned using L<fork> and L<exec>; it will not
580accumulate the times of suprocesses spawned via pipes, L<system>,
581or backticks.
583=item unlink LIST
585C<unlink> will delete the highest version of a file only; in
586order to delete all versions, you need to say
587 1 while (unlink LIST);
588You may need to make this change to scripts written for a
589Unix system which expect that after a call to C<unlink>,
590no files with the names passed to C<unlink> will exist.
591(Note: This can be changed at compile time; if you
592C<use Config> and C<$Config{'d_unlink_all_versions'}> is
593C<define>, then C<unlink> will delete all versions of a
594file on the first call.)
596C<unlink> will delete a file if at all possible, even if it
597requires changing file protection (though it won't try to
598change the protection of the parent directory). You can tell
599whether you've got explicit delete access to a file by using the
600C<VMS::Filespec::candelete> operator. For instance, in order
601to delete only files to which you have delete access, you could
602say something like
4e592037 603
604 sub safe_unlink {
605 my($file,$num);
606 foreach $file (@_) {
607 next unless VMS::Filespec::candelete($file);
608 $num += unlink $file;
609 }
610 $num;
611 }
4e592037 612
613(or you could just use C<VMS::Stdio::remove>, if you've installed
614the VMS::Stdio extension distributed with Perl). If C<unlink> has to
615change the file protection to delete the file, and you interrupt it
616in midstream, the file may be left intact, but with a changed ACL
617allowing you delete access.
16d20bd9 618
619=item utime LIST
621Since ODS-2, the VMS file structure for disk files, does not keep
622track of access times, this operator changes only the modification
623time of the file (VMS revision date).
625=item waitpid PID,FLAGS
627If PID is a subprocess started by a piped L<open>, C<waitpid>
628will wait for that subprocess, and return its final
629status value. If PID is a subprocess created in some other way
630(e.g. SPAWNed before Perl was invoked), or is not a subprocess of
631the current process, C<waitpid> will check once per second whether
632the process has completed, and when it has, will return 0. (If PID
633specifies a process that isn't a subprocess of the current process,
634and you invoked Perl with the C<-w> switch, a warning will be issued.)
636The FLAGS argument is ignored in all cases.
a0d0e21e 637
55497cff 638=back
640=head1 Perl variables
55497cff 642The following VMS-specific information applies to the indicated
643"special" Perl variables, in addition to the general information
644in L<perlvar>. Where there is a conflict, this infrmation
645takes precedence.
647=over 4
649=item %ENV
651Reading the elements of the %ENV array returns the
652translation of the logical name specified by the key,
653according to the normal search order of access modes and
654logical name tables. If you append a semicolon to the
655logical name, followed by an integer, that integer is
656used as the translation index for the logical name,
657so that you can look up successive values for search
658list logical names. For instance, if you say
660 $ Define STORY once,upon,a,time,there,was
661 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
740ce14c 662 _$ -e "{ print $ENV{'story;'.$i},' '}"
664Perl will print C<ONCE UPON A TIME THERE WAS>.
b7b1864f 666The key C<default> returns the current default device
a5f75d66 667and directory specification, regardless of whether
668there is a logical name DEFAULT defined. If you try to
669read an element of %ENV for which there is no corresponding
670logical name, and for which no corresponding CLI symbol
671exists (this is to identify "blocking" symbols only; to
672manipulate CLI symbols, see L<VMS::DCLSym>) then the key
673will be looked up in the CRTL-local environment array, and
674the corresponding value, if any returned. This lets you
675get at C-specific keys like C<home>, C<path>,C<term>, and
676C<user>, as well as other keys which may have been passed
677directly into the C-specific array if Perl was called from
678another C program using the version of execve() or execle()
679present in recent revisions of the DECCRTL.
681Setting an element of %ENV defines a supervisor-mode logical
682name in the process logical name table. C<Undef>ing or
683C<delete>ing an element of %ENV deletes the equivalent user-
684mode or supervisor-mode logical name from the process logical
685name table. If you use C<undef>, the %ENV element remains
686empty. If you use C<delete>, another attempt is made at
687logical name translation after the deletion, so an inner-mode
688logical name or a name in another logical name table will
689replace the logical name just deleted. It is not possible
690at present to define a search list logical name via %ENV.
691It is also not possible to delete an element from the
692C-local environ array.
694Note that if you want to pass on any elements of the
695C-local environ array to a subprocess which isn't
696started by fork/exec, or isn't running a C program, you
697can "promote" them to logical names in the current
698process, which will then be inherited by all subprocesses,
699by saying
701 foreach my $key (qw[C-local keys you want promoted]) {
702 my $temp = $ENV{$key}; # read from C-local array
703 $ENV{$key} = $temp; # and define as logical name
704 }
706(You can't just say C<$ENV{$key} = $ENV{$key}>, since the
707Perl optimizer is smart enough to elide the expression.)
a5f75d66 708
740ce14c 709At present, the first time you iterate over %ENV using
710C<keys>, or C<values>, you will incur a time penalty as all
711logical names are read, in order to fully populate %ENV.
712Subsequent iterations will not reread logical names, so they
713won't be as slow, but they also won't reflect any changes
714to logical name tables caused by other programs. The C<each>
715operator is special: it returns each element I<already> in
716%ENV, but doesn't go out and look for more. Therefore, if
717you've previously used C<keys> or C<values>, you'll see all
718the logical names visible to your process, and if not, you'll
719see only the names you've looked up so far. (This is a
720consequence of the way C<each> is implemented now, and it
721may change in the future, so it wouldn't be a good idea
722to rely on it too much.)
740ce14c 723
724In all operations on %ENV, the key string is treated as if it
725were entirely uppercase, regardless of the case actually
726specified in the Perl expression.
728=item $!
730The string value of C<$!> is that returned by the CRTL's
731strerror() function, so it will include the VMS message for
732VMS-specific errors. The numeric value of C<$!> is the
733value of C<errno>, except if errno is EVMSERR, in which
734case C<$!> contains the value of vaxc$errno. Setting C<$!>
4e592037 735always sets errno to the value specified. If this value is
736EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
737that the string value of C<$!> won't reflect the VMS error
738message from before C<$!> was set.
740=item $^E
742This variable provides direct access to VMS status values
743in vaxc$errno, which are often more specific than the
744generic Unix-style error messages in C<$!>. Its numeric value
745is the value of vaxc$errno, and its string value is the
746corresponding VMS message string, as retrieved by sys$getmsg().
747Setting C<$^E> sets vaxc$errno to the value specified.
4fdae800 749=item $?
751The "status value" returned in C<$?> is synthesized from the
752actual exit status of the subprocess in a way that approximates
753POSIX wait(5) semantics, in order to allow Perl programs to
754portably test for successful completion of subprocesses. The
755low order 8 bits of C<$?> are always 0 under VMS, since the
756termination status of a process may or may not have been
757generated by an exception. The next 8 bits are derived from
758severity portion of the subprocess' exit status: if the
759severity was success or informational, these bits are all 0;
760otherwise, they contain the severity value shifted left one bit.
761As a result, C<$?> will always be zero if the subprocess' exit
762status indicated successful completion, and non-zero if a
763warning or error occurred. The actual VMS exit status may
764be found in C<$^S> (q.v.).
766=item $^S
768Under VMS, this is the 32-bit VMS status value returned by the
769last subprocess to complete. Unlink C<$?>, no manipulation
770is done to make this look like a POSIX wait(5) value, so it
771may be treated as a normal VMS status value.
4e592037 773=item $|
775Setting C<$|> for an I/O stream causes data to be flushed
776all the way to disk on each write (I<i.e.> not just to
777the underlying RMS buffers for a file). In other words,
778it's equivalent to calling fflush() and fsync() from C.
a5f75d66 779
55497cff 780=back
782=head1 Standard modules with VMS-specific differences
784=head2 SDBM_File
786SDBM_File works peroperly on VMS. It has, however, one minor
787difference. The database directory file created has a L<.sdbm_dir>
788extension rather than a L<.dir> extension. L<.dir> files are VMS filesystem
789directory files, and using them for other purposes could cause unacceptable
748a9306 792=head1 Revision date
a0d0e21e 793
794This document was last updated on 26-Feb-1998, for Perl 5,
795patchlevel 5.
e518068a 796
797=head1 AUTHOR
bf99883d 799Charles Bailey
e518068a 800
bf99883d 801Last revision by Dan Sugalski