We hope these notes will save you from confusion and lost
sleep when writing Perl scripts on VMS. If you find we've
missed something you think should appear here, please don't
-hesitate to drop a line to vmsperl@newman.upenn.edu.
+hesitate to drop a line to vmsperl@perl.org.
=head1 Installation
I<N.B.> The procedure by which extensions are built and
tested creates several levels (at least 4) under the
directory in which the extension's source files live.
-For this reason, you shouldn't nest the source directory
-too deeply in your directory structure, lest you eccedd RMS'
+For this reason if you are running a version of VMS prior
+to V7.1 you shouldn't nest the source directory
+too deeply in your directory structure lest you exceed RMS'
maximum of 8 levels of subdirectory in a filespec. (You
can use rooted logical names to get another 8 levels of
nesting, if you can't place the files near the top of
be added to the linker options file F<PGPLOT.Opt> produced
during the build process for the Perl extension.
-By default, the shareable image for an extension is placed
-F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
+By default, the shareable image for an extension is placed in
+
the F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
F<VMS_AXP>, and I<Extname> is the name of the extension, with
each C<::> translated to C<.>). (See the MakeMaker documentation
for more details on installation options for extensions.)
However, it can be manually placed in any of several locations:
- - the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
- of one of the directories in C<@INC> (where I<PVers>
- is the version of Perl you're using, as supplied in C<$]>,
- with '.' converted to '_'), or
- - one of the directories in C<@INC>, or
- - a directory which the extensions Perl library module
- passes to the DynaLoader when asking it to map
- the shareable image, or
- - F<Sys$Share> or F<Sys$Library>.
+
+=over 4
+
+=item *
+
+the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
+of one of the directories in C<@INC> (where I<PVers>
+is the version of Perl you're using, as supplied in C<$]>,
+with '.' converted to '_'), or
+
+=item *
+
+one of the directories in C<@INC>, or
+
+=item *
+
+a directory which the extensions Perl library module
+passes to the DynaLoader when asking it to map
+the shareable image, or
+
+=item *
+
+F<Sys$Share> or F<Sys$Library>.
+
+=back
+
If the shareable image isn't in any of these places, you'll need
to define a logical name I<Extshortname>, where I<Extshortname>
is the portion of the extension's name after the last C<::>, which
We have tried to make Perl aware of both VMS-style and Unix-
style file specifications wherever possible. You may use
either style, or both, on the command line and in scripts,
-but you may not combine the two styles within a single fle
+but you may not combine the two styles within a single file
specification. VMS Perl interprets Unix pathnames in much
the same way as the CRTL (I<e.g.> the first component of
an absolute path is read as the device name for the
interconversion between VMS and Unix syntax; its
documentation provides more details.
-Filenames are, of course, still case-insensitive. For
-consistency, most Perl routines return filespecs using
-lower case letters only, regardless of the case used in
-the arguments passed to them. (This is true only when
-running under VMS; Perl respects the case-sensitivity
-of OSs like Unix.)
+Perl is now in the process of evolving to follow the setting of
+the DECC$* feature logical names in the interpretation of UNIX pathnames.
+This is still a work in progress.
+
+For handling extended characters, and case sensitivity, as long as
+DECC$POSIX_COMPLIANT_PATHNAMES, DECC$FILENAME_UNIX_REPORT, and
+DECC$FILENAME_UNIX_ONLY are not set, then the older Perl behavior
+for conversions of file specifications from UNIX to VMS is followed,
+except that VMS paths with concealed rooted logical names are now
+translated correctly to UNIX paths.
+
+With those features set, then new routines may handle the translation,
+because some of the rules are different. The presence of ./.../
+in a UNIX path is no longer translated to the VMS [...]. It will
+translate to [.^.^.^.]. To be compatible with what MakeMaker expects,
+if a VMS path can not be translated to a UNIX path when unixify
+is called, it is passed through unchanged. So unixify("[...]") will
+return "[...]".
+
+The handling of extended characters will also be better with the
+newer translation routines. But more work is needed to fully support
+extended file syntax names. In particular, at this writing Pathtools
+can not deal with directories containing some extended characters.
+
+There are several ambiguous cases where a conversion routine can not
+determine if an input filename is in UNIX format or in VMS format,
+since now both VMS UNIX file specifications can have characters in
+them that could be mistaken for syntax delimiters of the other type.
+So some pathnames simply can not be used in a mode that allows either
+type of pathname to be present.
+
+Perl will tend to assume that an ambiguous filename is in UNIX format.
+
+Allowing "." as a version delimiter is simply incompatible with
+determining if a pathname is already VMS format or UNIX with the
+extended file syntax. There is no way to know if "perl-5.8.6" that
+TAR produces is a UNIX "perl-5.8.6" or a VMS "perl-5.8;6" when
+passing it to unixify() or vmsify().
+
+The DECC$FILENAME_UNIX_REPORT or the DECC$FILENAME_UNIX_ONLY logical
+names control how Perl interprets filenames.
+
+The DECC$FILENAME_UNIX_ONLY setting has not been tested at this time.
+Perl uses traditional OpenVMS file specifications internally and in
+the test harness, so this mode may have limited use, or require more
+changes to make usable.
+
+Everything about DECC$FILENAME_UNIX_REPORT should be assumed to apply
+to DECC$FILENAME_UNIX_ONLY mode. The DECC$FILENAME_UNIX_ONLY differs
+in that it expects all filenames passed to the C runtime to be already
+in UNIX format.
+
+Again, currently most of the core Perl modules have not yet been updated
+to understand that VMS is not as limited as it use to be. Fixing that
+is a work in progress.
+
+The logical name DECC$POSIX_COMPLIANT_PATHNAMES is new with the
+RMS Symbolic Link SDK. This version of Perl does not support it being set.
+
+
+Filenames are case-insensitive on VAX, and on ODS-2 formatted
+volumes on ALPHA and I64.
+
+On ODS-5 volumes filenames are case preserved and on newer
+versions of OpenVMS can be optionally case sensitive.
+
+On ALPHA and I64, Perl is in the process of being changed to follow the
+process case sensitivity setting to report if the file system is case
+sensitive.
+
+Perl programs should not assume that VMS is case blind, or that
+filenames will be in lowercase.
+
+Programs should use the File::Spec:case_tolerant setting to determine
+the state, and not the $^O setting.
+
+For consistency, when the above feature is clear and when not
+otherwise overridden by DECC feature logical names, most Perl routines
+return file specifications using lower case letters only,
+regardless of the case used in the arguments passed to them.
+(This is true only when running under VMS; Perl respects the
+case-sensitivity of OSs like Unix.)
We've tried to minimize the dependence of Perl library
modules on Unix syntax, but you may find that some of these,
of this in the Perl distribution itself, please let us know,
so we can try to work around them.
+Also when working on Perl programs on VMS, if you need a syntax
+in a specific operating system format, then you need to either
+check the appropriate DECC$ feature logical, or call a conversion
+routine to force it to that format.
+
=head2 Wildcard expansion
File specifications containing wildcards are allowed both on
-the command line and within Perl globs (e.g. <CE<lt>*.cE<gt>>). If
+the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>). If
the wildcard filespec uses VMS syntax, the resultant
filespecs will follow VMS syntax; if a Unix-style filespec is
passed in, Unix-style filespecs will be returned.
+Similar to the behavior of wildcard globbing for a Unix shell,
+one can escape command line wildcards with double quotation
+marks C<"> around a perl program command line argument. However,
+owing to the stripping of C<"> characters carried out by the C
+handling of argv you will need to escape a construct such as
+this one (in a directory containing the files F<PERL.C>, F<PERL.EXE>,
+F<PERL.H>, and F<PERL.OBJ>):
-In both cases, VMS wildcard expansion is performed. (csh-style
+ $ perl -e "print join(' ',@ARGV)" perl.*
+ perl.c perl.exe perl.h perl.obj
+
+in the following triple quoted manner:
+
+ $ perl -e "print join(' ',@ARGV)" """perl.*"""
+ perl.*
+
+In both the case of unquoted command line arguments or in calls
+to C<glob()> VMS wildcard expansion is performed. (csh-style
wildcard expansion is available if you use C<File::Glob::glob>.)
If the wildcard filespec contains a device or directory
specification, then the resultant filespecs will also contain
Similarly, the resultant filespec will contain the file version
only if one was present in the input filespec.
+
=head2 Pipes
Input and output pipes to Perl filehandles are supported; the
argument to the C<system> operator (see below). In this case,
Perl will wait for the subprocess to complete before continuing.
+The mailbox (MBX) that perl can create to communicate with a pipe
+defaults to a buffer size of 512. The default buffer size is
+adjustable via the logical name PERL_MBX_SIZE provided that the
+value falls between 128 and the SYSGEN parameter MAXBUF inclusive.
+For example, to double the MBX size from the default within
+a Perl program, use C<$ENV{'PERL_MBX_SIZE'} = 1024;> and then
+open and use pipe constructs. An alternative would be to issue
+the command:
+
+ $ Define PERL_MBX_SIZE 1024
+
+before running your wide record pipe program. A larger value may
+improve performance at the expense of the BYTLM UAF quota.
+
=head1 PERL5LIB and PERLLIB
-The PERL5LIB and PERLLIB logical names work as documented L<perl>,
+The PERL5LIB and PERLLIB logical names work as documented
in L<perl>,
except that the element separator is '|' instead of ':'. The
directory specifications may use either VMS or Unix syntax.
Perl for VMS supports redirection of input and output on the
command line, using a subset of Bourne shell syntax:
- <F<file> reads stdin from F<file>,
- >F<file> writes stdout to F<file>,
- >>F<file> appends stdout to F<file>,
- 2>F<file> writes stderr to F<file>, and
- 2>>F<file> appends stderr to F<file>.
+=over 4
+
+=item *
+
+C<E<lt>file> reads stdin from C<file>,
+
+=item *
+
+C<E<gt>file> writes stdout to C<file>,
+
+=item *
+
+C<E<gt>E<gt>file> appends stdout to C<file>,
+
+=item *
+
+C<2E<gt>file> writes stderr to C<file>,
+
+=item *
+
+C<2E<gt>E<gt>file> appends stderr to C<file>, and
+
+=item *
+
+C<< 2>&1 >> redirects stderr to stdout.
+
+=back
In addition, output may be piped to a subprocess, using the
character '|'. Anything after this character on the command
them in double-quotes on the command line, since the CRTL
downcases all unquoted strings.
+On newer 64 bit versions of OpenVMS, a process setting now
+controls if the quoting is needed to preserve the case of
+command line arguments.
+
=over 4
=item -i
=item -S
-If the C<-S> switch is present I<and> the script name does
-not contain a directory, then Perl translates the logical
-name DCL$PATH as a searchlist, using each translation as
-a directory in which to look for the script. In addition,
+If the C<"-S"> or C<-"S"> switch is present I<and> the script
+name does not contain a directory, then Perl translates the
+logical name DCL$PATH as a searchlist, using each translation
+as a directory in which to look for the script. In addition,
if no file type is specified, Perl looks in each directory
for a file matching the name specified, with a blank type,
a type of F<.pl>, and a type of F<.com>, in that order.
caller, chdir, chmod, chown, chomp, chop, chr,
close, closedir, cos, crypt*, defined, delete,
die, do, dump*, each, endpwent, eof, eval, exec*,
- exists, exit, exp, fileno, fork*, getc, getlogin,
+ exists, exit, exp, fileno, getc, getlogin, getppid,
getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
grep, hex, import, index, int, join, keys, kill*,
last, lc, lcfirst, length, local, localtime, log, m//,
and calling them produces a fatal error (usually) or
undefined behavior (rarely, we hope):
- chroot, dbmclose, dbmopen, fcntl, flock,
- getpgrp, getppid, getpriority, getgrent, getgrgid,
+ chroot, dbmclose, dbmopen, flock, fork*,
+ getpgrp, getpriority, getgrent, getgrgid,
getgrnam, setgrent, endgrent, ioctl, link, lstat,
msgctl, msgget, msgsend, msgrcv, readlink, semctl,
semget, semop, setpgrp, setpriority, shmctl, shmget,
shmread, shmwrite, socketpair, symlink, syscall
-The following functions are available on Perls compiled with Dec C 5.2 or
-greater and running VMS 7.0 or greater
+The following functions are available on Perls compiled with Dec C
+5.2 or greater and running VMS 7.0 or greater:
truncate
+The following functions are available on Perls built on VMS 7.2 or
+greater:
+
+ fcntl (without locking)
+
The following functions may or may not be implemented,
depending on what type of socket support you've built into
your copy of Perl:
getsockopt, listen, recv, select(system call)*,
send, setsockopt, shutdown, socket
+The following function is available on Perls built on 64 bit OpenVMS 8.2
+with hard links enabled on an ODS-5 formatted build disk. If someone with
+an OpenVMS 7.3-1 system were to modify configure.com and test the results,
+this feature can be brought back to OpenVMS 7.3-1 and later. Hardlinks
+must be enabled on the build disk because if the build procedure sees
+this feature enabled, it uses it.
+
+ link
+
+The following functions are available on Perls built on 64 bit OpenVMS
+8.2 and can be implemented on OpenVMS 7.3-2 if someone were to modify
+configure.com and test the results. (While in the build, at the time
+of this writing, they have not been specifically tested.)
+
+ getgrgid, getgrnam, getpwnam, getpwuid,
+ setgrent, ttyname
+
+The following functions are available on Perls built on 64 bit OpenVMS 8.2
+and later. (While in the build, at the time of this writing, they have
+not been specifically tested.)
+
+ statvfs, socketpair
+
+The following functions are expected to soon be available on Perls built
+on 64 bit OpenVMS 8.2 or later with the RMS Symbolic link package. Use
+of symbolic links at this time effectively requires the
+DECC$POSIX_COMPLIANT_PATHNAMES to defined as 3, and operating in a
+DECC$FILENAME_UNIX_REPORT mode.
+
+ lchown, link, lstat, readlink, symlink
+
=over 4
=item File tests
specification without an explicit directory (e.g. C<DUA1:>), as
well as if passed a directory.
+There are DECC feature logical names AND ODS-5 volume attributes that
+also control what values are returned for the date fields.
+
Note: Some sites have reported problems when using the file-access
tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
Specifically, since DFS does not currently provide access to the
password strings; you'll have to upcase the arguments to
C<crypt> to insure that you'll get the proper value:
- sub validate_passwd {
- my($user,$passwd) = @_;
- my($pwdhash);
- if ( !($pwdhash = (getpwnam($user))[1]) ||
- $pwdhash ne crypt("\U$passwd","\U$name") ) {
- intruder_alert($name);
+ sub validate_passwd {
+ my($user,$passwd) = @_;
+ my($pwdhash);
+ if ( !($pwdhash = (getpwnam($user))[1]) ||
+ $pwdhash ne crypt("\U$passwd","\U$name") ) {
+ intruder_alert($name);
+ }
+ return 1;
}
- return 1;
- }
+
+
+=item die
+
+C<die> will force the native VMS exit status to be an SS$_ABORT code
+if neither of the $! or $? status values are ones that would cause
+the native status to be interpreted as being what VMS classifies as
+SEVERE_ERROR severity for DCL error handling.
+
+When the future POSIX_EXIT mode is active, C<die>, the native VMS exit
+status value will have either one of the C<$!> or C<$?> or C<$^E> or
+the UNIX value 255 encoded into it in a way that the effective original
+value can be decoded by other programs written in C, including Perl
+and the GNV package. As per the normal non-VMS behavior of C<die> if
+either C<$!> or C<$?> are non-zero, one of those values will be
+encoded into a native VMS status value. If both of the UNIX status
+values are 0, and the C<$^E> value is set one of ERROR or SEVERE_ERROR
+severity, then the C<$^E> value will be used as the exit code as is.
+If none of the above apply, the UNIX value of 255 will be encoded into
+a native VMS exit status value.
+
+Please note a significant difference in the behavior of C<die> in
+the future POSIX_EXIT mode is that it does not force a VMS
+SEVERE_ERROR status on exit. The UNIX exit values of 2 through
+255 will be encoded in VMS status values with severity levels of
+SUCCESS. The UNIX exit value of 1 will be encoded in a VMS status
+value with a severity level of ERROR. This is to be compatible with
+how the VMS C library encodes these values.
+
+The minimum severity level set by C<die> in a future POSIX_EXIT mode
+may be changed to be ERROR or higher before that mode becomes fully active
+depending on the results of testing and further review. If this is
+done, the behavior of c<DIE> in the future POSIX_EXIT will close enough
+to the default mode that most DCL shell scripts will probably not notice
+a difference.
+
+See C<$?> for a description of the encoding of the UNIX value to
+produce a native VMS status containing it.
+
=item dump
=item exec LIST
-The C<exec> operator behaves in one of two different ways.
-If called after a call to C<fork>, it will invoke the CRTL
-C<execv()> routine, passing its arguments to the subprocess
-created by C<fork> for execution. In this case, it is
-subject to all limitations that affect C<execv()>. (In
-particular, this usually means that the command executed in
-the subprocess must be an image compiled from C source code,
-and that your options for passing file descriptors and signal
-handlers to the subprocess are limited.)
-
-If the call to C<exec> does not follow a call to C<fork>, it
-will cause Perl to exit, and to invoke the command given as
-an argument to C<exec> via C<lib$do_command>. If the argument
-begins with '@' or '$' (other than as part of a filespec), then it
-is executed as a DCL command. Otherwise, the first token on
-the command line is treated as the filespec of an image to
-run, and an attempt is made to invoke it (using F<.Exe> and
-the process defaults to expand the filespec) and pass the
-rest of C<exec>'s argument to it as parameters. If the token
-has no file type, and matches a file with null type, then an
-attempt is made to determine whether the file is an executable
-image which should be invoked using C<MCR> or a text file which
-should be passed to DCL as a command procedure.
-
-You can use C<exec> in both ways within the same script, as
-long as you call C<fork> and C<exec> in pairs. Perl
-keeps track of how many times C<fork> and C<exec> have been
-called, and will call the CRTL C<execv()> routine if there have
-previously been more calls to C<fork> than to C<exec>.
+A call to C<exec> will cause Perl to exit, and to invoke the command
+given as an argument to C<exec> via C<lib$do_command>. If the
+argument begins with '@' or '$' (other than as part of a filespec),
+then it is executed as a DCL command. Otherwise, the first token on
+the command line is treated as the filespec of an image to run, and
+an attempt is made to invoke it (using F<.Exe> and the process
+defaults to expand the filespec) and pass the rest of C<exec>'s
+argument to it as parameters. If the token has no file type, and
+matches a file with null type, then an attempt is made to determine
+whether the file is an executable image which should be invoked
+using C<MCR> or a text file which should be passed to DCL as a
+command procedure.
=item fork
-The C<fork> operator works in the same way as the CRTL
-C<vfork()> routine, which is quite different under VMS than
-under Unix. Specifically, while C<fork> returns 0 after it
-is called and the subprocess PID after C<exec> is called, in
-both cases the thread of execution is within the parent
-process, so there is no opportunity to perform operations in
-the subprocess before calling C<exec>.
-
-In general, the use of C<fork> and C<exec> to create
-subprocess is not recommended under VMS; wherever possible,
-use the C<system> operator or piped filehandles instead.
+While in principle the C<fork> operator could be implemented via
+(and with the same rather severe limitations as) the CRTL C<vfork()>
+routine, and while some internal support to do just that is in
+place, the implementation has never been completed, making C<fork>
+currently unavailable. A true kernel C<fork()> is expected in a
+future version of VMS, and the pseudo-fork based on interpreter
+threads may be available in a future version of Perl on VMS (see
+L<perlfork>). In the meantime, use C<system>, backticks, or piped
+filehandles to create subprocesses.
=item getpwent
=item kill
-In most cases, C<kill> kill is implemented via the CRTL's C<kill()>
+In most cases, C<kill> is implemented via the CRTL's C<kill()>
function, so it will behave according to that function's
documentation. If you send a SIGKILL, however, the $DELPRC system
service is called directly. This insures that the target
Perl waits for the subprocess to complete before continuing
execution in the current process. As described in L<perlfunc>,
the return value of C<system> is a fake "status" which follows
-POSIX semantics; see the description of C<$?> in this document
-for more detail. The actual VMS exit status of the subprocess
-is available in C<$^S> (as long as you haven't used another Perl
-function that resets C<$?> and C<$^S> in the meantime).
+POSIX semantics unless the pragma C<use vmsish 'status'> is in
+effect; see the description of C<$?> in this document for more
+detail.
=item time
according to the same rules the CRTL C<times()> routine.
Therefore, the "system time" elements will always be 0, since
there is no difference between "user time" and "system" time
-under VMS, and the time accumulated by subprocess may or may
+under VMS, and the time accumulated by a subprocess may or may
not appear separately in the "child time" field, depending on
whether L<times> keeps track of subprocesses separately. Note
especially that the VAXCRTL (at least) keeps track only of
C<unlink> will delete the highest version of a file only; in
order to delete all versions, you need to say
- 1 while (unlink LIST);
+
+ 1 while unlink LIST;
+
You may need to make this change to scripts written for a
Unix system which expect that after a call to C<unlink>,
no files with the names passed to C<unlink> will exist.
in midstream, the file may be left intact, but with a changed ACL
allowing you delete access.
+This behavior of C<unlink> is to be compatible with POSIX behavior
+and not traditional VMS behavior.
+
=item utime LIST
Since ODS-2, the VMS file structure for disk files, does not keep
=item waitpid PID,FLAGS
-If PID is a subprocess started by a piped L<open>, C<waitpid>
-will wait for that subprocess, and return its final
-status value. If PID is a subprocess created in some other way
-(e.g. SPAWNed before Perl was invoked), or is not a subprocess of
-the current process, C<waitpid> will check once per second whether
-the process has completed, and when it has, will return 0. (If PID
-specifies a process that isn't a subprocess of the current process,
+If PID is a subprocess started by a piped C<open()> (see L<open>),
+C<waitpid> will wait for that subprocess, and return its final status
+value in C<$?>. If PID is a subprocess created in some other way (e.g.
+SPAWNed before Perl was invoked), C<waitpid> will simply check once per
+second whether the process has completed, and return when it has. (If
+PID specifies a process that isn't a subprocess of the current process,
and you invoked Perl with the C<-w> switch, a warning will be issued.)
-The FLAGS argument is ignored in all cases.
+Returns PID on success, -1 on error. The FLAGS argument is ignored
+in all cases.
=back
by the global symbol table.. The characters following C<CLISYM_> are
significant when an element of C<%ENV> is set or deleted: if the
complete string is C<CLISYM_LOCAL>, the change is made in the local
-symbol table, otherwise the global symbol table is changed.
+symbol table; otherwise the global symbol table is changed.
=item Any other string
present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
to see whether your copy of Perl was built with a CRTL that has this
function.)
-
+
When an element of C<%ENV> is set to C<undef>,
the element is looked up as if it were being read, and if it is
found, it is deleted. (An item "deleted" from the CRTL C<environ>
by saying
foreach my $key (qw[C-local keys you want promoted]) {
- my $temp = $ENV{$key}; # read from C-local array
- $ENV{$key} = $temp; # and define as logical name
+ my $temp = $ENV{$key}; # read from C-local array
+ $ENV{$key} = $temp; # and define as logical name
}
(You can't just say C<$ENV{$key} = $ENV{$key}>, since the
Perl optimizer is smart enough to elide the expression.)
+Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
+a fatal error. This is equivalent to doing the following from DCL:
+
+ DELETE/LOGICAL *
+
+You can imagine how bad things would be if, for example, the SYS$MANAGER
+or SYS$SYSTEM logical names were deleted.
+
At present, the first time you iterate over %ENV using
C<keys>, or C<values>, you will incur a time penalty as all
logical names are read, in order to fully populate %ENV.
won't be as slow, but they also won't reflect any changes
to logical name tables caused by other programs.
-You do need to be careful with the logicals representing process-permanent
-files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
-logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
-stripped off if you want to use it. (In previous versions of perl it wasn't
-possible to get the values of these logicals, as the null byte acted as an
-end-of-string marker)
+You do need to be careful with the logical names representing
+process-permanent files, such as C<SYS$INPUT> and C<SYS$OUTPUT>.
+The translations for these logical names are prepended with a
+two-byte binary value (0x1B 0x00) that needs to be stripped off
+if you wantto use it. (In previous versions of Perl it wasn't
+possible to get the values of these logical names, as the null
+byte acted as an end-of-string marker)
=item $!
corresponding VMS message string, as retrieved by sys$getmsg().
Setting C<$^E> sets vaxc$errno to the value specified.
+While Perl attempts to keep the vaxc$errno value to be current, if
+errno is not EVMSERR, it may not be from the current operation.
+
=item $?
The "status value" returned in C<$?> is synthesized from the
portably test for successful completion of subprocesses. The
low order 8 bits of C<$?> are always 0 under VMS, since the
termination status of a process may or may not have been
-generated by an exception. The next 8 bits are derived from
-severity portion of the subprocess' exit status: if the
-severity was success or informational, these bits are all 0;
-otherwise, they contain the severity value shifted left one bit.
-As a result, C<$?> will always be zero if the subprocess' exit
-status indicated successful completion, and non-zero if a
-warning or error occurred. The actual VMS exit status may
-be found in C<$^S> (q.v.).
+generated by an exception.
-=item $^S
+The next 8 bits contain the termination status of the program.
-Under VMS, this is the 32-bit VMS status value returned by the
-last subprocess to complete. Unlink C<$?>, no manipulation
-is done to make this look like a POSIX wait(5) value, so it
-may be treated as a normal VMS status value.
+If the child process follows the convention of C programs
+compiled with the _POSIX_EXIT macro set, the status value will
+contain the actual value of 0 to 255 returned by that program
+on a normal exit.
+
+With the _POSIX_EXIT macro set, the UNIX exit value of zero is
+represented as a VMS native status of 1, and the UNIX values
+from 2 to 255 are encoded by the equation:
+
+ VMS_status = 0x35a000 + (unix_value * 8) + 1.
+
+And in the special case of unix value 1 the encoding is:
+
+ VMS_status = 0x35a000 + 8 + 2 + 0x10000000.
+
+For other termination statuses, the severity portion of the
+subprocess' exit status is used: if the severity was success or
+informational, these bits are all 0; if the severity was
+warning, they contain a value of 1; if the severity was
+error or fatal error, they contain the actual severity bits,
+which turns out to be a value of 2 for error and 4 for severe_error.
+Fatal is another term for the severe_error status.
+
+As a result, C<$?> will always be zero if the subprocess' exit
+status indicated successful completion, and non-zero if a
+warning or error occurred or a program compliant with encoding
+_POSIX_EXIT values was run and set a status.
+
+How can you tell the difference between a non-zero status that is
+the result of a VMS native error status or an encoded UNIX status?
+You can not unless you look at the ${^CHILD_ERROR_NATIVE} value.
+The ${^CHILD_ERROR_NATIVE} value returns the actual VMS status value
+and check the severity bits. If the severity bits are equal to 1,
+then if the numeric value for C<$?> is between 2 and 255 or 0, then
+C<$?> accurately reflects a value passed back from a UNIX application.
+If C<$?> is 1, and the severity bits indicate a VMS error (2), then
+C<$?> is from a UNIX application exit value.
+
+In practice, Perl scripts that call programs that return _POSIX_EXIT
+type status values will be expecting those values, and programs that
+call traditional VMS programs will either be expecting the previous
+behavior or just checking for a non-zero status.
+
+And success is always the value 0 in all behaviors.
+
+When the actual VMS termination status of the child is an error,
+internally the C<$!> value will be set to the closest UNIX errno
+value to that error so that Perl scripts that test for error
+messages will see the expected UNIX style error message instead
+of a VMS message.
+
+Conversely, when setting C<$?> in an END block, an attempt is made
+to convert the POSIX value into a native status intelligible to
+the operating system upon exiting Perl. What this boils down to
+is that setting C<$?> to zero results in the generic success value
+SS$_NORMAL, and setting C<$?> to a non-zero value results in the
+generic failure status SS$_ABORT. See also L<perlport/exit>.
+
+With the future POSIX_EXIT mode set, setting C<$?> will cause the
+new value to also be encoded into C<$^E> so that the either the
+original parent or child exit status values of 0 to 255
+can be automatically recovered by C programs expecting _POSIX_EXIT
+behavior. If both a parent and a child exit value are non-zero, then it
+will be assumed that this is actually a VMS native status value to
+be passed through. The special value of 0xFFFF is almost a NOOP as
+it will cause the current native VMS status in the C library to
+become the current native Perl VMS status, and is handled this way
+as consequence of it known to not be a valid native VMS status value.
+It is recommend that only values in range of normal UNIX parent or
+child status numbers, 0 to 255 are used.
+
+The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
+VMS exit status instead of the default emulation of POSIX status
+described above. This pragma also disables the conversion of
+non-zero values to SS$_ABORT when setting C<$?> in an END
+block (but zero will still be converted to SS$_NORMAL).
+
+Do not use the pragma C<use vmsish 'status'> with the future
+POSIX_EXIT mode, as they are at times requesting conflicting
+actions and the consequence of ignoring this advice will be
+undefined to allow future improvements in the POSIX exit handling.
=item $|
=head1 Revision date
-This document was last updated on 26-Feb-2000, for Perl 5,
-patchlevel 6.
+This document was last updated on 14-Oct-2005, for Perl 5,
+patchlevel 8.
=head1 AUTHOR
-Charles Bailey <bailey@cor.newman.upenn.edu>
-Dan Sugalski <dan@sidhe.org>
+Charles Bailey bailey@cor.newman.upenn.edu
+Craig Berry craigberry@mac.com
+Dan Sugalski dan@sidhe.org
+John Malmberg wb8tyw@qsl.net
https://perl5.git.perl.org / perl5.git / blobdiff