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1=head1 NAME
2
3perlvms - VMS-specific documentation for Perl
4
5=head1 DESCRIPTION
a0d0e21e 6
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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.
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16
17We hope these notes will save you from confusion and lost
748a9306 18sleep when writing Perl scripts on VMS. If you find we've
a0d0e21e 19missed something you think should appear here, please don't
f675dbe5 20hesitate to drop a line to vmsperl@newman.upenn.edu.
a0d0e21e 21
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22=head1 Installation
23
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..
27
e518068a 28=head1 Organization of Perl Images
748a9306 29
e518068a 30=head2 Core Images
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31
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.
38
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.)
48
49
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.
55
56=head2 Perl Extensions
57
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
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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.
66
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.
78
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.
87
e518068a 88=head2 Installing static extensions
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89
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.
99
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).
106
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107=head2 Installing dynamic extensions
108
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
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114directory, and the procedure for building the extension is simply
115
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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
120
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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.)
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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.
141
142By default, the shareable image for an extension is placed
bbce6d69 143F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
e518068a 144installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
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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:
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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
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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.
162
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-
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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
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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.
178
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
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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,
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192so we can try to work around them.
193
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194=head2 Wildcard expansion
195
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.
201
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.)
214
215Similarly, the resultant filespec will contain the file version
216only if one was present in the input filespec.
217
218=head2 Pipes
219
220Input and output pipes to Perl filehandles are supported; the
221"file name" is passed to lib$spawn() for asynchronous
222execution. You should be careful to close any pipes you have
223opened in a Perl script, lest you leave any "orphaned"
224subprocesses around when Perl exits.
225
226You may also use backticks to invoke a DCL subprocess, whose
227output is used as the return value of the expression. The
228string between the backticks is passed directly to lib$spawn
229as the command to execute. In this case, Perl will wait for
230the subprocess to complete before continuing.
231
232=head1 PERL5LIB and PERLLIB
233
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.
237
238=head1 Command line
239
240=head2 I/O redirection and backgrounding
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241
242Perl for VMS supports redirection of input and output on the
243command line, using a subset of Bourne shell syntax:
55497cff 244
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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
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249 2>>F<file> appends stderr to F<file>.
250
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.
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255
256Finally, if the command line ends with '&', the entire
257command is run in the background as an asynchronous
258subprocess.
259
4e592037 260=head2 Command line switches
a0d0e21e 261
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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
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268=over 4
269
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270=item -i
271
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.)
278
4e592037 279=item -S
a0d0e21e 280
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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
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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
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295=back
296
748a9306 297=head1 Perl functions
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298
299As of the time this document was last revised, the following
748a9306 300Perl functions were implemented in the VMS port of Perl
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301(functions marked with * are discussed in more detail below):
302
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,
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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,
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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///
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322
323The following functions were not implemented in the VMS port,
324and calling them produces a fatal error (usually) or
325undefined behavior (rarely, we hope):
326
4e592037 327 chroot, dbmclose, dbmopen, fcntl, flock,
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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,
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332 shmread, shmwrite, socketpair, symlink, syscall
333
334The following functions are available on Perls compiled with Dec C 5.2 or
335greater and running VMS 7.0 or greater
336
337 truncate
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338
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
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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,
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350 getsockopt, listen, recv, select(system call)*,
351 send, setsockopt, shutdown, socket
a0d0e21e 352
55497cff 353=over 4
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354
355=item File tests
356
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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.
371
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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.
382
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383=item backticks
384
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$spawn()>, any valid DCL command string
388may be specified.
389
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390=item binmode FILEHANDLE
391
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392The C<binmode> operator will attempt to insure that no translation
393of carriage control occurs on input from or output to this filehandle.
394Since this involves reopening the file and then restoring its
395file position indicator, if this function returns FALSE, the
396underlying filehandle may no longer point to an open file, or may
397point to a different position in the file than before C<binmode>
398was called.
399
400Note that C<binmode> is generally not necessary when using normal
401filehandles; it is provided so that you can control I/O to existing
402record-structured files when necessary. You can also use the
403C<vmsfopen> function in the VMS::Stdio extension to gain finer
404control of I/O to files and devices with different record structures.
a0d0e21e 405
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406=item crypt PLAINTEXT, USER
407
408The C<crypt> operator uses the C<sys$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.
414
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:
422
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 }
432
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433=item dump
434
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>.
443
748a9306 444=item exec LIST
a0d0e21e 445
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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
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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.)
455
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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$do_command>. If the argument
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459begins with a '$' (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
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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>.
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471
472=item fork
473
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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
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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,
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484use the C<system> operator or piped filehandles instead.
485
486=item getpwent
c07a80fd 487
748a9306 488=item getpwnam
c07a80fd 489
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490=item getpwuid
491
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
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501=item gmtime
502
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.
510
511=item kill
512
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
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517process is actually deleted, if at all possible. (The CRTL's C<kill()>
518function is presently implemented via $FORCEX, which is ignored by
519supervisor-mode images like DCL.)
520
521Also, negative signal values don't do anything special under
522VMS; they're just converted to the corresponding positive value.
523
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524=item qx//
525
526See the entry on C<backticks> above.
527
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528=item select (system call)
529
530If Perl was not built with socket support, the system call
531version of C<select> is not available at all. If socket
532support is present, then the system call version of
533C<select> functions only for file descriptors attached
534to sockets. It will not provide information about regular
535files or pipes, since the CRTL C<select()> routine does not
536provide this functionality.
537
748a9306 538=item stat EXPR
a0d0e21e 539
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540Since VMS keeps track of files according to a different scheme
541than Unix, it's not really possible to represent the file's ID
542in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
543tries its best, though, and the values it uses are pretty unlikely
544to be the same for two different files. We can't guarantee this,
545though, so caveat scriptor.
546
547=item system LIST
548
549The C<system> operator creates a subprocess, and passes its
a0d0e21e 550arguments to the subprocess for execution as a DCL command.
e518068a 551Since the subprocess is created directly via C<lib$spawn()>, any
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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
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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
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563=item time
564
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.
568
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569=item times
570
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571The array returned by the C<times> operator is divided up
572according to the same rules the CRTL C<times()> routine.
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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
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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.
582
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583=item unlink LIST
584
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.
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591(Note: This can be changed at compile time; if you
592C<use Config> and C<$Config{'d_unlink_all_versions'}> is
593C<define>, then C<unlink> will delete all versions of a
594file on the first call.)
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595
596C<unlink> will delete a file if at all possible, even if it
597requires changing file protection (though it won't try to
598change the protection of the parent directory). You can tell
599whether you've got explicit delete access to a file by using the
600C<VMS::Filespec::candelete> operator. For instance, in order
601to delete only files to which you have delete access, you could
602say something like
4e592037 603
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604 sub safe_unlink {
605 my($file,$num);
606 foreach $file (@_) {
607 next unless VMS::Filespec::candelete($file);
608 $num += unlink $file;
609 }
610 $num;
611 }
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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
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619=item utime LIST
620
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).
624
625=item waitpid PID,FLAGS
626
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.)
635
636The FLAGS argument is ignored in all cases.
a0d0e21e 637
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638=back
639
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640=head1 Perl variables
641
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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.
646
647=over 4
648
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649=item %ENV
650
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651The operation of the C<%ENV> array depends on the translation
652of the logical name F<PERL_ENV_TABLES>. If defined, it should
653be a search list, each element of which specifies a location
654for C<%ENV> elements. If you tell Perl to read or set the
655element C<$ENV{>I<name>C<}>, then Perl uses the translations of
656F<PERL_ENV_TABLES> as follows:
657
658=over 4
659
660=item CRTL_ENV
661
662This string tells Perl to consult the CRTL's internal C<environ>
663array of key-value pairs, using I<name> as the key. In most cases,
664this contains only a few keys, but if Perl was invoked via the C
665C<exec[lv]e()> function, as is the case for CGI processing by some
666HTTP servers, then the C<environ> array may have been populated by
667the calling program.
668
669=item CLISYM_[LOCAL]
670
671A string beginning with C<CLISYM_>tells Perl to consult the CLI's
672symbol tables, using I<name> as the name of the symbol. When reading
673an element of C<%ENV>, the local symbol table is scanned first, followed
674by the global symbol table.. The characters following C<CLISYM_> are
675significant when an element of C<%ENV> is set or deleted: if the
676complete string is C<CLISYM_LOCAL>, the change is made in the local
677symbol table, otherwise the global symbol table is changed.
678
679=item Any other string
680
681If an element of F<PERL_ENV_TABLES> translates to any other string,
682that string is used as the name of a logical name table, which is
683consulted using I<name> as the logical name. The normal search
684order of access modes is used.
685
686=back
687
688F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
689you make while Perl is running do not affect the behavior of C<%ENV>.
690If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
691first the logical name tables specified by F<LNM$FILE_DEV>, and then
692the CRTL C<environ> array.
693
694In all operations on %ENV, the key string is treated as if it
695were entirely uppercase, regardless of the case actually
696specified in the Perl expression.
697
698When an element of C<%ENV> is read, the locations to which
699F<PERL_ENV_TABLES> points are checked in order, and the value
700obtained from the first successful lookup is returned. If the
701name of the C<%ENV> element contains a semi-colon, it and
702any characters after it are removed. These are ignored when
703the CRTL C<environ> array or a CLI symbol table is consulted.
704However, the name is looked up in a logical name table, the
705suffix after the semi-colon is treated as the translation index
706to be used for the lookup. This lets you look up successive values
707for search list logical names. For instance, if you say
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708
709 $ Define STORY once,upon,a,time,there,was
710 $ perl -e "for ($i = 0; $i <= 6; $i++) " -
740ce14c 711 _$ -e "{ print $ENV{'story;'.$i},' '}"
a5f75d66 712
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713Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
714that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
715is found, rather than a CLI symbol or CRTL C<environ> element with
716the same name.
717
3eeba6fb 718When an element of C<%ENV> is set to a defined string, the
f675dbe5
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719corresponding definition is made in the location to which the
720first translation of F<PERL_ENV_TABLES> points. If this causes a
721logical name to be created, it is defined in supervisor mode.
3eeba6fb
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722(The same is done if an existing logical name was defined in
723executive or kernel mode; an existing user or supervisor mode
724logical name is reset to the new value.) If the value is an empty
725string, the logical name's translation is defined as a single NUL
726(ASCII 00) character, since a logical name cannot translate to a
727zero-length string. (This restriction does not apply to CLI symbols
728or CRTL C<environ> values; they are set to the empty string.)
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729An element of the CRTL C<environ> array can be set only if your
730copy of Perl knows about the CRTL's C<setenv()> function. (This is
731present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
732to see whether your copy of Perl was built with a CRTL that has this
733function.)
734
3eeba6fb 735When an element of C<%ENV> is set to C<undef>,
f675dbe5
CB
736the element is looked up as if it were being read, and if it is
737found, it is deleted. (An item "deleted" from the CRTL C<environ>
738array is set to the empty string; this can only be done if your
739copy of Perl knows about the CRTL C<setenv()> function.) Using
740C<delete> to remove an element from C<%ENV> has a similar effect,
741but after the element is deleted, another attempt is made to
742look up the element, so an inner-mode logical name or a name in
743another location will replace the logical name just deleted.
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744In either case, only the first value found searching PERL_ENV_TABLES
745is altered. It is not possible at present to define a search list
746logical name via %ENV.
f675dbe5
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747
748The element C<$ENV{DEFAULT}> is special: when read, it returns
749Perl's current default device and directory, and when set, it
750resets them, regardless of the definition of F<PERL_ENV_TABLES>.
751It cannot be cleared or deleted; attempts to do so are silently
752ignored.
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753
754Note that if you want to pass on any elements of the
755C-local environ array to a subprocess which isn't
756started by fork/exec, or isn't running a C program, you
757can "promote" them to logical names in the current
758process, which will then be inherited by all subprocesses,
759by saying
760
761 foreach my $key (qw[C-local keys you want promoted]) {
762 my $temp = $ENV{$key}; # read from C-local array
763 $ENV{$key} = $temp; # and define as logical name
764 }
765
766(You can't just say C<$ENV{$key} = $ENV{$key}>, since the
767Perl optimizer is smart enough to elide the expression.)
a5f75d66 768
740ce14c 769At present, the first time you iterate over %ENV using
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770C<keys>, or C<values>, you will incur a time penalty as all
771logical names are read, in order to fully populate %ENV.
772Subsequent iterations will not reread logical names, so they
773won't be as slow, but they also won't reflect any changes
f675dbe5
CB
774to logical name tables caused by other programs.
775
776You do need to be careful with the logicals representing process-permanent
777files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
778logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
779stripped off if you want to use it. (In previous versions of perl it wasn't
780possible to get the values of these logicals, as the null byte acted as an
781end-of-string marker)
a5f75d66 782
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783=item $!
784
785The string value of C<$!> is that returned by the CRTL's
786strerror() function, so it will include the VMS message for
787VMS-specific errors. The numeric value of C<$!> is the
788value of C<errno>, except if errno is EVMSERR, in which
789case C<$!> contains the value of vaxc$errno. Setting C<$!>
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790always sets errno to the value specified. If this value is
791EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
792that the string value of C<$!> won't reflect the VMS error
793message from before C<$!> was set.
794
795=item $^E
796
797This variable provides direct access to VMS status values
798in vaxc$errno, which are often more specific than the
799generic Unix-style error messages in C<$!>. Its numeric value
800is the value of vaxc$errno, and its string value is the
801corresponding VMS message string, as retrieved by sys$getmsg().
802Setting C<$^E> sets vaxc$errno to the value specified.
803
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804=item $?
805
806The "status value" returned in C<$?> is synthesized from the
807actual exit status of the subprocess in a way that approximates
808POSIX wait(5) semantics, in order to allow Perl programs to
809portably test for successful completion of subprocesses. The
810low order 8 bits of C<$?> are always 0 under VMS, since the
811termination status of a process may or may not have been
812generated by an exception. The next 8 bits are derived from
813severity portion of the subprocess' exit status: if the
814severity was success or informational, these bits are all 0;
815otherwise, they contain the severity value shifted left one bit.
816As a result, C<$?> will always be zero if the subprocess' exit
817status indicated successful completion, and non-zero if a
818warning or error occurred. The actual VMS exit status may
819be found in C<$^S> (q.v.).
820
821=item $^S
822
823Under VMS, this is the 32-bit VMS status value returned by the
824last subprocess to complete. Unlink C<$?>, no manipulation
825is done to make this look like a POSIX wait(5) value, so it
826may be treated as a normal VMS status value.
827
4e592037
PP
828=item $|
829
830Setting C<$|> for an I/O stream causes data to be flushed
831all the way to disk on each write (I<i.e.> not just to
832the underlying RMS buffers for a file). In other words,
833it's equivalent to calling fflush() and fsync() from C.
a5f75d66 834
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835=back
836
bf99883d
HM
837=head1 Standard modules with VMS-specific differences
838
839=head2 SDBM_File
840
841SDBM_File works peroperly on VMS. It has, however, one minor
842difference. The database directory file created has a L<.sdbm_dir>
843extension rather than a L<.dir> extension. L<.dir> files are VMS filesystem
844directory files, and using them for other purposes could cause unacceptable
845problems.
846
748a9306 847=head1 Revision date
a0d0e21e 848
bf99883d
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849This document was last updated on 26-Feb-1998, for Perl 5,
850patchlevel 5.
e518068a
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851
852=head1 AUTHOR
853
bf99883d 854Charles Bailey bailey@cor.newman.upenn.edu
e518068a 855
bf99883d 856Last revision by Dan Sugalski sugalskd@ous.edu