NAME¶
perlvms - VMS-specific documentation for Perl
DESCRIPTION¶
Gathered below are notes describing details of Perl 5's behavior on VMS. They
are a supplement to the regular Perl 5 documentation, so we have focussed on
the ways in which Perl 5 functions differently under VMS than it does under
Unix, and on the interactions between Perl and the rest of the operating
system. We haven't tried to duplicate complete descriptions of Perl features
from the main Perl documentation, which can be found in the
[.pod]
subdirectory of the Perl distribution.
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@perl.org.
Installation¶
Directions for building and installing Perl 5 can be found in the file
README.vms in the main source directory of the Perl distribution..
Organization of Perl Images¶
Core Images¶
During the installation process, three Perl images are produced.
Miniperl.Exe is an executable image which contains all of the basic
functionality of Perl, but cannot take advantage of Perl extensions. It is
used to generate several files needed to build the complete Perl and various
extensions. Once you've finished installing Perl, you can delete this image.
Most of the complete Perl resides in the shareable image
PerlShr.Exe,
which provides a core to which the Perl executable image and all Perl
extensions are linked. You should place this image in
Sys$Share, or
define the logical name
PerlShr to translate to the full file
specification of this image. It should be world readable. (Remember that if a
user has execute only access to
PerlShr, VMS will treat it as if it
were a privileged shareable image, and will therefore require all downstream
shareable images to be INSTALLed, etc.)
Finally,
Perl.Exe is an executable image containing the main entry point
for Perl, as well as some initialization code. It should be placed in a public
directory, and made world executable. In order to run Perl with command line
arguments, you should define a foreign command to invoke this image.
Perl Extensions¶
Perl extensions are packages which provide both XS and Perl code to add new
functionality to perl. (XS is a meta-language which simplifies writing C code
which interacts with Perl, see perlxs for more details.) The Perl code for an
extension is treated like any other library module - it's made available in
your script through the appropriate "use" or "require"
statement, and usually defines a Perl package containing the extension.
The portion of the extension provided by the XS code may be connected to the
rest of Perl in either of two ways. In the
static configuration, the
object code for the extension is linked directly into
PerlShr.Exe, and
is initialized whenever Perl is invoked. In the
dynamic configuration,
the extension's machine code is placed into a separate shareable image, which
is mapped by Perl's DynaLoader when the extension is "use"d or
"require"d in your script. This allows you to maintain the extension
as a separate entity, at the cost of keeping track of the additional shareable
image. Most extensions can be set up as either static or dynamic.
The source code for an extension usually resides in its own directory. At least
three files are generally provided:
Extshortname.xs (where
Extshortname is the portion of the extension's name following the last
"::"), containing the XS code,
Extshortname.pm, the
Perl library module for the extension, and
Makefile.PL, a Perl script
which uses the "MakeMaker" library modules supplied with Perl to
generate a
Descrip.MMS file for the extension.
Installing static extensions¶
Since static extensions are incorporated directly into
PerlShr.Exe,
you'll have to rebuild Perl to incorporate a new extension. You should edit
the main
Descrip.MMS or
Makefile you use to build Perl, adding
the extension's name to the "ext" macro, and the extension's object
file to the "extobj" macro. You'll also need to build the
extension's object file, either by adding dependencies to the main
Descrip.MMS, or using a separate
Descrip.MMS for the extension.
Then, rebuild
PerlShr.Exe to incorporate the new code.
Finally, you'll need to copy the extension's Perl library module to the
[. Extname] subdirectory under one of the directories in
@INC, where
Extname is the name of the extension, with all
"::" replaced by "." (e.g. the library module for
extension Foo::Bar would be copied to a
[.Foo.Bar] subdirectory).
Installing dynamic extensions¶
In general, the distributed kit for a Perl extension includes a file named
Makefile.PL, which is a Perl program which is used to create a
Descrip.MMS file which can be used to build and install the files
required by the extension. The kit should be unpacked into a directory tree
not under the main Perl source directory, and the procedure for
building the extension is simply
$ perl Makefile.PL ! Create Descrip.MMS
$ mmk ! Build necessary files
$ mmk test ! Run test code, if supplied
$ mmk install ! Install into public Perl tree
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 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 the physical directory
structure.)
VMS support for this process in the current release of Perl is sufficient to
handle most extensions. However, it does not yet recognize extra libraries
required to build shareable images which are part of an extension, so these
must be added to the linker options file for the extension by hand. For
instance, if the
PGPLOT extension to Perl requires the
PGPLOTSHR.EXE shareable image in order to properly link the Perl
extension, then the line "PGPLOTSHR/Share" must be added to the
linker options file
PGPLOT.Opt produced during the build process for
the Perl extension.
By default, the shareable image for an extension is placed in the
[.lib.site_perl.auto Arch.
Extname] directory of
the installed Perl directory tree (where
Arch is
VMS_VAX or
VMS_AXP, and
Extname is the name of the extension, with each
"::" translated to "."). (See the MakeMaker documentation
for more details on installation options for extensions.) However, it can be
manually placed in any of several locations:
- •
- the
[.Lib.Auto.Arch$PVersExtname]
subdirectory of one of the directories in @INC (where PVers is the
version of Perl you're using, as supplied in $], with '.' converted to
'_'), or
- •
- one of the directories in @INC, or
- •
- a directory which the extensions Perl library module passes to the
DynaLoader when asking it to map the shareable image, or
- •
- Sys$Share or Sys$Library.
If the shareable image isn't in any of these places, you'll need to define a
logical name
Extshortname, where
Extshortname is the portion of
the extension's name after the last "::", which translates to the
full file specification of the shareable image.
File specifications¶
Syntax¶
We have tried to make Perl aware of both VMS-style and Unix-style file
specifications wherever possible. You may use either style, or both, on the
command line and in scripts, but you may not combine the two styles within a
single file specification. VMS Perl interprets Unix pathnames in much the same
way as the CRTL (
e.g. the first component of an absolute path is read
as the device name for the VMS file specification). There are a set of
functions provided in the "VMS::Filespec" package for explicit
interconversion between VMS and Unix syntax; its documentation provides more
details.
We've tried to minimize the dependence of Perl library modules on Unix syntax,
but you may find that some of these, as well as some scripts written for Unix
systems, will require that you use Unix syntax, since they will assume that
'/' is the directory separator,
etc. If you find instances of this in
the Perl distribution itself, please let us know, so we can try to work around
them.
Also when working on Perl programs on VMS, if you need a syntax in a specific
operating system format, then you need either to check the appropriate DECC$
feature logical, or call a conversion routine to force it to that format.
The feature logical name DECC$FILENAME_UNIX_REPORT modifies traditional Perl
behavior in the conversion of file specifications from Unix to VMS format in
order to follow the extended character handling rules now expected by the
CRTL. Specifically, when this feature is in effect, the "./.../" in
a Unix path is now translated to "[.^.^.^.]" instead of the
traditional VMS "[...]". To be compatible with what MakeMaker
expects, if a VMS path cannot be translated to a Unix path, it is passed
through unchanged, so "unixify("[...]")" will return
"[...]".
The handling of extended characters is largely complete in the VMS-specific C
infrastructure of Perl, but more work is still needed to fully support
extended syntax filenames in several core modules. In particular, at this
writing PathTools has only partial support for directories containing some
extended characters.
There are several ambiguous cases where a conversion routine cannot determine
whether an input filename is in Unix format or in VMS format, since now both
VMS and Unix file specifications may have characters in them that could be
mistaken for syntax delimiters of the other type. So some pathnames simply
cannot be used in a mode that allows either type of pathname to be present.
Perl will tend to assume that an ambiguous filename is in Unix format.
Allowing "." as a version delimiter is simply incompatible with
determining whether a pathname is in VMS format or in Unix format with
extended file syntax. There is no way to know whether "perl-5.8.6"
is a Unix "perl-5.8.6" or a VMS "perl-5.8;6" when passing
it to
unixify() or
vmsify().
The DECC$FILENAME_UNIX_REPORT logical name controls how Perl interprets
filenames to the extent that Perl uses the CRTL internally for many purposes,
and attempts to follow CRTL conventions for reporting filenames. The
DECC$FILENAME_UNIX_ONLY feature differs in that it expects all filenames
passed to the C run-time to be already in Unix format. This feature is not yet
supported in Perl since Perl uses traditional OpenVMS file specifications
internally and in the test harness, and it is not yet clear whether this mode
will be useful or useable. The feature logical name
DECC$POSIX_COMPLIANT_PATHNAMES is new with the RMS Symbolic Link SDK and
included with OpenVMS v8.3, but is not yet supported in Perl.
Filename Case¶
Perl follows VMS defaults and override settings in preserving (or not
preserving) filename case. Case is not preserved on ODS-2 formatted volumes on
any architecture. On ODS-5 volumes, filenames may be case preserved depending
on process and feature settings. Perl now honors DECC$EFS_CASE_PRESERVE and
DECC$ARGV_PARSE_STYLE on those systems where the CRTL supports these features.
When these features are not enabled or the CRTL does not support them, Perl
follows the traditional CRTL behavior of downcasing command-line arguments and
returning file specifications in lower case only.
N. B. It is very easy to get tripped up using a mixture of other
programs, external utilities, and Perl scripts that are in varying states of
being able to handle case preservation. For example, a file created by an
older version of an archive utility or a build utility such as MMK or MMS may
generate a filename in all upper case even on an ODS-5 volume. If this
filename is later retrieved by a Perl script or module in a case preserving
environment, that upper case name may not match the mixed-case or lower-case
exceptions of the Perl code. Your best bet is to follow an all-or-nothing
approach to case preservation: either don't use it at all, or make sure your
entire toolchain and application environment support and use it.
OpenVMS Alpha v7.3-1 and later and all version of OpenVMS I64 support case
sensitivity as a process setting (see "SET PROCESS
/CASE_LOOKUP=SENSITIVE"). Perl does not currently support case
sensitivity on VMS, but it may in the future, so Perl programs should use the
"File::Spec->case_tolerant" method to determine the state, and
not the $^O variable.
Symbolic Links¶
When built on an ODS-5 volume with symbolic links enabled, Perl by default
supports symbolic links when the requisite support is available in the
filesystem and CRTL (generally 64-bit OpenVMS v8.3 and later). There are a
number of limitations and caveats to be aware of when working with symbolic
links on VMS. Most notably, the target of a valid symbolic link must be
expressed as a Unix-style path and it must exist on a volume visible from your
POSIX root (see the "SHOW ROOT" command in DCL help). For further
details on symbolic link capabilities and requirements, see chapter 12 of the
CRTL manual that ships with OpenVMS v8.3 or later.
Wildcard expansion¶
File specifications containing wildcards are allowed both on the command line
and within Perl globs (e.g. "<*.c>"). 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 """ around a
perl program command line argument. However, owing to the stripping of
""" 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
PERL.C,
PERL.EXE,
PERL.H, and
PERL.OBJ):
$ 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
"glob()" VMS wildcard expansion is performed. (csh-style wildcard
expansion is available if you use "File::Glob::glob".) If the
wildcard filespec contains a device or directory specification, then the
resultant filespecs will also contain a device and directory; otherwise,
device and directory information are removed. VMS-style resultant filespecs
will contain a full device and directory, while Unix-style resultant filespecs
will contain only as much of a directory path as was present in the input
filespec. For example, if your default directory is Perl_Root:[000000], the
expansion of "[.t]*.*" will yield filespecs like
"perl_root:[t]base.dir", while the expansion of "t/*/*"
will yield filespecs like "t/base.dir". (This is done to match the
behavior of glob expansion performed by Unix shells.)
Similarly, the resultant filespec will contain the file version only if one was
present in the input filespec.
Pipes¶
Input and output pipes to Perl filehandles are supported; the "file
name" is passed to lib$
spawn() for asynchronous execution. You
should be careful to close any pipes you have opened in a Perl script, lest
you leave any "orphaned" subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose output is used as
the return value of the expression. The string between the backticks is
handled as if it were the argument to the "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 8192 on 64-bit systems, 512 on VAX. 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 set the
mailbox size to 32767 use "$ENV{'PERL_MBX_SIZE'} = 32767;" and then
open and use pipe constructs. An alternative would be to issue the command:
$ Define PERL_MBX_SIZE 32767
before running your wide record pipe program. A larger value may improve
performance at the expense of the BYTLM UAF quota.
PERL5LIB and PERLLIB¶
The PERL5LIB and PERLLIB logical names work as documented in perl, except that
the element separator is '|' instead of ':'. The directory specifications may
use either VMS or Unix syntax.
The Perl Forked Debugger¶
The Perl forked debugger places the debugger commands and output in a separate
X-11 terminal window so that commands and output from multiple processes are
not mixed together.
Perl on VMS supports an emulation of the forked debugger when Perl is run on a
VMS system that has X11 support installed.
To use the forked debugger, you need to have the default display set to an X-11
Server and some environment variables set that Unix expects.
The forked debugger requires the environment variable "TERM" to be
"xterm", and the environment variable "DISPLAY" to exist.
"xterm" must be in lower case.
$define TERM "xterm"
$define DISPLAY "hostname:0.0"
Currently the value of "DISPLAY" is ignored. It is recommended that it
be set to be the hostname of the display, the server and screen in Unix
notation. In the future the value of DISPLAY may be honored by Perl instead of
using the default display.
It may be helpful to always use the forked debugger so that script I/O is
separated from debugger I/O. You can force the debugger to be forked by
assigning a value to the logical name <PERLDB_PIDS> that is not a
process identification number.
$define PERLDB_PIDS XXXX
PERL_VMS_EXCEPTION_DEBUG¶
The PERL_VMS_EXCEPTION_DEBUG being defined as "ENABLE" will cause the
VMS debugger to be invoked if a fatal exception that is not otherwise handled
is raised. The purpose of this is to allow debugging of internal Perl problems
that would cause such a condition.
This allows the programmer to look at the execution stack and variables to find
out the cause of the exception. As the debugger is being invoked as the Perl
interpreter is about to do a fatal exit, continuing the execution in debug
mode is usually not practical.
Starting Perl in the VMS debugger may change the program execution profile in a
way that such problems are not reproduced.
The "kill" function can be used to test this functionality from within
a program.
In typical VMS style, only the first letter of the value of this logical name is
actually checked in a case insensitive mode, and it is considered enabled if
it is the value "T","1" or "E".
This logical name must be defined before Perl is started.
Command line¶
I/O redirection and backgrounding¶
Perl for VMS supports redirection of input and output on the command line, using
a subset of Bourne shell syntax:
- •
- "<file" reads stdin from "file",
- •
- ">file" writes stdout to "file",
- •
- ">>file" appends stdout to "file",
- •
- "2>file" writes stderr to "file",
- •
- "2>>file" appends stderr to "file", and
- •
- "2>&1" redirects stderr to stdout.
In addition, output may be piped to a subprocess, using the character '|'.
Anything after this character on the command line is passed to a subprocess
for execution; the subprocess takes the output of Perl as its input.
Finally, if the command line ends with '&', the entire command is run in the
background as an asynchronous subprocess.
Command line switches¶
The following command line switches behave differently under VMS than described
in perlrun. Note also that in order to pass uppercase switches to Perl, you
need to enclose 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.
- -i
- If the "-i" switch is present but no extension for a backup copy
is given, then inplace editing creates a new version of a file; the
existing copy is not deleted. (Note that if an extension is given, an
existing file is renamed to the backup file, as is the case under other
operating systems, so it does not remain as a previous version under the
original filename.)
- -S
- If the "-S" or "-"S"" switch is present
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 .pl, and
a type of .com, in that order.
- -u
- The "-u" switch causes the VMS debugger to be invoked after the
Perl program is compiled, but before it has run. It does not create a core
dump file.
Perl functions¶
As of the time this document was last revised, the following Perl functions were
implemented in the VMS port of Perl (functions marked with * are discussed in
more detail below):
file tests*, abs, alarm, atan, backticks*, binmode*, bless,
caller, chdir, chmod, chown, chomp, chop, chr,
close, closedir, cos, crypt*, defined, delete, die, do, dump*,
each, endgrent, endpwent, eof, eval, exec*, exists, exit, exp,
fileno, flock getc, getgrent*, getgrgid*, getgrnam, getlogin,
getppid, getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
grep, hex, ioctl, import, index, int, join, keys, kill*,
last, lc, lcfirst, lchown*, length, link*, local, localtime, log,
lstat, m//, map, mkdir, my, next, no, oct, open, opendir, ord,
pack, pipe, pop, pos, print, printf, push, q//, qq//, qw//,
qx//*, quotemeta, rand, read, readdir, readlink*, redo, ref,
rename, require, reset, return, reverse, rewinddir, rindex,
rmdir, s///, scalar, seek, seekdir, select(internal),
select (system call)*, setgrent, setpwent, shift, sin, sleep,
socketpair, sort, splice, split, sprintf, sqrt, srand, stat,
study, substr, symlink*, sysread, system*, syswrite, tell,
telldir, tie, time, times*, tr///, uc, ucfirst, umask,
undef, unlink*, unpack, untie, unshift, use, utime*,
values, vec, wait, waitpid*, wantarray, warn, write, y///
The following functions were not implemented in the VMS port, and calling them
produces a fatal error (usually) or undefined behavior (rarely, we hope):
chroot, dbmclose, dbmopen, fork*, getpgrp, getpriority,
msgctl, msgget, msgsend, msgrcv, semctl,
semget, semop, setpgrp, setpriority, shmctl, shmget,
shmread, shmwrite, syscall
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:
accept, bind, connect, getpeername,
gethostbyname, getnetbyname, getprotobyname,
getservbyname, gethostbyaddr, getnetbyaddr,
getprotobynumber, getservbyport, gethostent,
getnetent, getprotoent, getservent, sethostent,
setnetent, setprotoent, setservent, endhostent,
endnetent, endprotoent, endservent, getsockname,
getsockopt, listen, recv, select(system call)*,
send, setsockopt, shutdown, socket
The following function is available on Perls built on 64 bit OpenVMS v8.2 with
hard links enabled on an ODS-5 formatted build disk. CRTL support is in
principle available as of OpenVMS v7.3-1, and better configuration support
could detect this.
link
The following functions are available on Perls built on 64 bit OpenVMS v8.2 and
later. CRTL support is in principle available as of OpenVMS v7.3-2, and better
configuration support could detect this.
getgrgid, getgrnam, getpwnam, getpwuid,
setgrent, ttyname
The following functions are available on Perls built on 64 bit OpenVMS v8.2 and
later.
statvfs, socketpair
- File tests
- The tests "-b", "-B", "-c", "-C",
"-d", "-e", "-f", "-o",
"-M", "-s", "-S", "-t",
"-T", and "-z" work as advertised. The return values
for "-r", "-w", and "-x" tell you whether
you can actually access the file; this may not reflect the UIC-based file
protections. Since real and effective UIC don't differ under VMS,
"-O", "-R", "-W", and "-X" are
equivalent to "-o", "-r", "-w", and
"-x". Similarly, several other tests, including "-A",
"-g", "-k", "-l", "-p", and
"-u", aren't particularly meaningful under VMS, and the values
returned by these tests reflect whatever your CRTL "stat()"
routine does to the equivalent bits in the st_mode field. Finally,
"-d" returns true if passed a device specification without an
explicit directory (e.g. "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
("-r", "-w", and "-x") on files accessed via
DEC's DFS. Specifically, since DFS does not currently provide access to
the extended file header of files on remote volumes, attempts to examine
the ACL fail, and the file tests will return false, with $! indicating
that the file does not exist. You can use "stat" on these files,
since that checks UIC-based protection only, and then manually check the
appropriate bits, as defined by your C compiler's stat.h, in the
mode value it returns, if you need an approximation of the file's
protections.
- backticks
- Backticks create a subprocess, and pass the enclosed string to it for
execution as a DCL command. Since the subprocess is created directly via
"lib$spawn()", any valid DCL command string may be
specified.
- binmode FILEHANDLE
- The "binmode" operator will attempt to insure that no
translation of carriage control occurs on input from or output to this
filehandle. Since this involves reopening the file and then restoring its
file position indicator, if this function returns FALSE, the underlying
filehandle may no longer point to an open file, or may point to a
different position in the file than before "binmode" was called.
Note that "binmode" is generally not necessary when using normal
filehandles; it is provided so that you can control I/O to existing
record-structured files when necessary. You can also use the
"vmsfopen" function in the VMS::Stdio extension to gain finer
control of I/O to files and devices with different record structures.
- crypt PLAINTEXT, USER
- The "crypt" operator uses the "sys$hash_password"
system service to generate the hashed representation of PLAINTEXT. If USER
is a valid username, the algorithm and salt values are taken from that
user's UAF record. If it is not, then the preferred algorithm and a salt
of 0 are used. The quadword encrypted value is returned as an 8-character
string.
The value returned by "crypt" may be compared against the
encrypted password from the UAF returned by the "getpw*"
functions, in order to authenticate users. If you're going to do this,
remember that the encrypted password in the UAF was generated using
uppercase username and password strings; you'll have to upcase the
arguments to "crypt" to insure that you'll get the proper value:
sub validate_passwd {
my($user,$passwd) = @_;
my($pwdhash);
if ( !($pwdhash = (getpwnam($user))[1]) ||
$pwdhash ne crypt("\U$passwd","\U$name") ) {
intruder_alert($name);
}
return 1;
}
- die
- "die" will force the native VMS exit status to be an SS$_ABORT
code if neither of the $! or $? status values are ones that would cause
the native status to be interpreted as being what VMS classifies as
SEVERE_ERROR severity for DCL error handling.
When "PERL_VMS_POSIX_EXIT" is active (see "$?" below),
the native VMS exit status value will have either one of the $! or $? or
$^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
"die" if either $! or $? 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 $^E value is set one of ERROR or SEVERE_ERROR
severity, then the $^E value will be used as the exit code as is. If none
of the above apply, the Unix value of 255 will be encoded into a native
VMS exit status value.
Please note a significant difference in the behavior of "die" in
the "PERL_VMS_POSIX_EXIT" mode is that it does not force a VMS
SEVERE_ERROR status on exit. The Unix exit values of 2 through 255 will be
encoded in VMS status values with severity levels of SUCCESS. The Unix
exit value of 1 will be encoded in a VMS status value with a severity
level of ERROR. This is to be compatible with how the VMS C library
encodes these values.
The minimum severity level set by "die" in
"PERL_VMS_POSIX_EXIT" mode may be changed to be ERROR or higher
in the future depending on the results of testing and further review.
See "$?" for a description of the encoding of the Unix value to
produce a native VMS status containing it.
- dump
- Rather than causing Perl to abort and dump core, the "dump"
operator invokes the VMS debugger. If you continue to execute the Perl
program under the debugger, control will be transferred to the label
specified as the argument to "dump", or, if no label was
specified, back to the beginning of the program. All other state of the
program ( e.g. values of variables, open file handles) are not
affected by calling "dump".
- exec LIST
- A call to "exec" will cause Perl to exit, and to invoke the
command given as an argument to "exec" via
"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 .Exe
and the process defaults to expand the filespec) and pass the rest of
"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 "MCR" or a text file which should be passed to DCL as a
command procedure.
- fork
- While in principle the "fork" operator could be implemented via
(and with the same rather severe limitations as) the CRTL
"vfork()" routine, and while some internal support to do just
that is in place, the implementation has never been completed, making
"fork" currently unavailable. A true kernel "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 perlfork). In the meantime, use "system", backticks, or
piped filehandles to create subprocesses.
- getpwent
- getpwnam
- getpwuid
- These operators obtain the information described in perlfunc, if you have
the privileges necessary to retrieve the named user's UAF information via
"sys$getuai". If not, then only the $name, $uid, and $gid items
are returned. The $dir item contains the login directory in VMS syntax,
while the $comment item contains the login directory in Unix syntax. The
$gcos item contains the owner field from the UAF record. The $quota item
is not used.
- gmtime
- The "gmtime" operator will function properly if you have a
working CRTL "gmtime()" routine, or if the logical name
SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds which must
be added to UTC to yield local time. (This logical name is defined
automatically if you are running a version of VMS with built-in UTC
support.) If neither of these cases is true, a warning message is printed,
and "undef" is returned.
- kill
- In most cases, "kill" is implemented via the undocumented system
service $SIGPRC, which has the same calling sequence as $FORCEX, but
throws an exception in the target process rather than forcing it to call
$EXIT. Generally speaking, "kill" follows the behavior of the
CRTL's "kill()" function, but unlike that function can be called
from within a signal handler. Also, unlike the "kill" in some
versions of the CRTL, Perl's "kill" checks the validity of the
signal passed in and returns an error rather than attempting to send an
unrecognized signal.
Also, negative signal values don't do anything special under VMS; they're
just converted to the corresponding positive value.
- qx//
- See the entry on "backticks" above.
- select (system call)
- If Perl was not built with socket support, the system call version of
"select" is not available at all. If socket support is present,
then the system call version of "select" functions only for file
descriptors attached to sockets. It will not provide information about
regular files or pipes, since the CRTL "select()" routine does
not provide this functionality.
- stat EXPR
- Since VMS keeps track of files according to a different scheme than Unix,
it's not really possible to represent the file's ID in the
"st_dev" and "st_ino" fields of a "struct
stat". Perl tries its best, though, and the values it uses are pretty
unlikely to be the same for two different files. We can't guarantee this,
though, so caveat scriptor.
- system LIST
- The "system" operator creates a subprocess, and passes its
arguments to the subprocess for execution as a DCL command. Since the
subprocess is created directly via "lib$spawn()", any valid DCL
command string may be specified. If the string begins with '@', it is
treated as a DCL command unconditionally. Otherwise, if the first token
contains a character used as a delimiter in file specification (e.g.
":" or "]"), an attempt is made to expand it using a
default type of .Exe and the process defaults, and if successful,
the resulting file is invoked via "MCR". This allows you to
invoke an image directly simply by passing the file specification to
"system", a common Unixish idiom. 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
"MCR" or a text file which should be passed to DCL as a command
procedure.
If LIST consists of the empty string, "system" spawns an
interactive DCL subprocess, in the same fashion as typing SPAWN at
the DCL prompt.
Perl waits for the subprocess to complete before continuing execution in the
current process. As described in perlfunc, the return value of
"system" is a fake "status" which follows POSIX
semantics unless the pragma "use vmsish 'status'" is in effect;
see the description of $? in this document for more detail.
- time
- The value returned by "time" is the offset in seconds from
01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in
order to make life easier for code coming in from the POSIX/Unix
world.
- times
- The array returned by the "times" operator is divided up
according to the same rules the CRTL "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 a
subprocess may or may not appear separately in the "child time"
field, depending on whether "times()" keeps track of
subprocesses separately. Note especially that the VAXCRTL (at least) keeps
track only of subprocesses spawned using "fork()" and
"exec()"; it will not accumulate the times of subprocesses
spawned via pipes, "system()", or backticks.
- unlink LIST
- "unlink" will delete the highest version of a file only; in
order to delete all versions, you need to say
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 "unlink", no files with the names
passed to "unlink" will exist. (Note: This can be changed at
compile time; if you "use Config" and
$Config{'d_unlink_all_versions'} is "define", then
"unlink" will delete all versions of a file on the first call.)
"unlink" will delete a file if at all possible, even if it
requires changing file protection (though it won't try to change the
protection of the parent directory). You can tell whether you've got
explicit delete access to a file by using the
"VMS::Filespec::candelete" operator. For instance, in order to
delete only files to which you have delete access, you could say something
like
sub safe_unlink {
my($file,$num);
foreach $file (@_) {
next unless VMS::Filespec::candelete($file);
$num += unlink $file;
}
$num;
}
(or you could just use "VMS::Stdio::remove", if you've installed
the VMS::Stdio extension distributed with Perl). If "unlink" has
to change the file protection to delete the file, and you interrupt it in
midstream, the file may be left intact, but with a changed ACL allowing
you delete access.
This behavior of "unlink" is to be compatible with POSIX behavior
and not traditional VMS behavior.
- utime LIST
- This operator changes only the modification time of the file (VMS revision
date) on ODS-2 volumes and ODS-5 volumes without access dates enabled. On
ODS-5 volumes with access dates enabled, the true access time is
modified.
- waitpid PID,FLAGS
- If PID is a subprocess started by a piped "open()" (see open),
"waitpid" will wait for that subprocess, and return its final
status value in $?. If PID is a subprocess created in some other way (e.g.
SPAWNed before Perl was invoked), "waitpid" will simply check
once per second whether the process has completed, and return when it has.
(If PID specifies a process that isn't a subprocess of the current
process, and you invoked Perl with the "-w" switch, a warning
will be issued.)
Returns PID on success, -1 on error. The FLAGS argument is ignored in all
cases.
Perl variables¶
The following VMS-specific information applies to the indicated
"special" Perl variables, in addition to the general information in
perlvar. Where there is a conflict, this information takes precedence.
- %ENV
- The operation of the %ENV array depends on the translation of the logical
name PERL_ENV_TABLES. If defined, it should be a search list, each
element of which specifies a location for %ENV elements. If you tell Perl
to read or set the element "$ENV{" name"}",
then Perl uses the translations of PERL_ENV_TABLES as follows:
- CRTL_ENV
- This string tells Perl to consult the CRTL's internal "environ"
array of key-value pairs, using name as the key. In most cases,
this contains only a few keys, but if Perl was invoked via the C
"exec[lv]e()" function, as is the case for CGI processing by
some HTTP servers, then the "environ" array may have been
populated by the calling program.
- CLISYM_[LOCAL]
- A string beginning with "CLISYM_"tells Perl to consult the CLI's
symbol tables, using name as the name of the symbol. When reading
an element of %ENV, the local symbol table is scanned first, followed by
the global symbol table.. The characters following "CLISYM_" are
significant when an element of %ENV is set or deleted: if the complete
string is "CLISYM_LOCAL", the change is made in the local symbol
table; otherwise the global symbol table is changed.
- Any other string
- If an element of PERL_ENV_TABLES translates to any other string,
that string is used as the name of a logical name table, which is
consulted using name as the logical name. The normal search order
of access modes is used.
PERL_ENV_TABLES is translated once when Perl starts up; any changes you
make while Perl is running do not affect the behavior of %ENV. If
PERL_ENV_TABLES is not defined, then Perl defaults to consulting first
the logical name tables specified by
LNM$FILE_DEV, and then the CRTL
"environ" array.
In all operations on %ENV, the key string is treated as if it were entirely
uppercase, regardless of the case actually specified in the Perl expression.
When an element of %ENV is read, the locations to which
PERL_ENV_TABLES
points are checked in order, and the value obtained from the first successful
lookup is returned. If the name of the %ENV element contains a semi-colon, it
and any characters after it are removed. These are ignored when the CRTL
"environ" array or a CLI symbol table is consulted. However, the
name is looked up in a logical name table, the suffix after the semi-colon is
treated as the translation index to be used for the lookup. This lets you look
up successive values for search list logical names. For instance, if you say
$ Define STORY once,upon,a,time,there,was
$ perl -e "for ($i = 0; $i <= 6; $i++) " -
_$ -e "{ print $ENV{'story;'.$i},' '}"
Perl will print "ONCE UPON A TIME THERE WAS", assuming, of course,
that
PERL_ENV_TABLES is set up so that the logical name
"story" is found, rather than a CLI symbol or CRTL
"environ" element with the same name.
When an element of %ENV is set to a defined string, the corresponding definition
is made in the location to which the first translation of
PERL_ENV_TABLES points. If this causes a logical name to be created, it
is defined in supervisor mode. (The same is done if an existing logical name
was defined in executive or kernel mode; an existing user or supervisor mode
logical name is reset to the new value.) If the value is an empty string, the
logical name's translation is defined as a single "NUL" (ASCII
"\0") character, since a logical name cannot translate to a
zero-length string. (This restriction does not apply to CLI symbols or CRTL
"environ" values; they are set to the empty string.) An element of
the CRTL "environ" array can be set only if your copy of Perl knows
about the CRTL's "setenv()" function. (This is present only in some
versions of the DECCRTL; check $Config{d_setenv} to see whether your copy of
Perl was built with a CRTL that has this function.)
When an element of %ENV is set to "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 "environ" array is set to the
empty string; this can only be done if your copy of Perl knows about the CRTL
"setenv()" function.) Using "delete" to remove an element
from %ENV has a similar effect, but after the element is deleted, another
attempt is made to look up the element, so an inner-mode logical name or a
name in another location will replace the logical name just deleted. In either
case, only the first value found searching PERL_ENV_TABLES is altered. It is
not possible at present to define a search list logical name via %ENV.
The element $ENV{DEFAULT} is special: when read, it returns Perl's current
default device and directory, and when set, it resets them, regardless of the
definition of
PERL_ENV_TABLES. It cannot be cleared or deleted;
attempts to do so are silently ignored.
Note that if you want to pass on any elements of the C-local environ array to a
subprocess which isn't started by fork/exec, or isn't running a C program, you
can "promote" them to logical names in the current process, which
will then be inherited by all subprocesses, 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
}
(You can't just say $ENV{$key} = $ENV{$key}, since the Perl optimizer is smart
enough to elide the expression.)
Don't try to clear %ENV by saying "%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 "keys", or
"values", you will incur a time penalty as all logical names are
read, in order to fully populate %ENV. Subsequent iterations will not reread
logical names, so they 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 logical names representing process-permanent
files, such as "SYS$INPUT" and "SYS$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 want to 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)
- $!
- The string value of $! is that returned by the CRTL's strerror()
function, so it will include the VMS message for VMS-specific errors. The
numeric value of $! is the value of "errno", except if errno is
EVMSERR, in which case $! contains the value of vaxc$errno. Setting $!
always sets errno to the value specified. If this value is EVMSERR, it
also sets vaxc$errno to 4 (NONAME-F-NOMSG), so that the string value of $!
won't reflect the VMS error message from before $! was set.
- $^E
- This variable provides direct access to VMS status values in vaxc$errno,
which are often more specific than the generic Unix-style error messages
in $!. Its numeric value is the value of vaxc$errno, and its string value
is the corresponding VMS message string, as retrieved by sys$
getmsg(). Setting $^E sets vaxc$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.
- $?
- The "status value" returned in $? is synthesized from the actual
exit status of the subprocess in a way that approximates POSIX
wait(5) semantics, in order to allow Perl programs to portably test
for successful completion of subprocesses. The low order 8 bits of $? 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 contain the termination status of the program.
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's
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, $? will always be zero if the subprocess's 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 $? is
between 2 and 255 or 0, then $? accurately reflects a value passed back
from a Unix application. If $? is 1, and the severity bits indicate a VMS
error (2), then $? 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 $! 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 $? 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 $? to zero
results in the generic success value SS$_NORMAL, and setting $? to a
non-zero value results in the generic failure status SS$_ABORT. See also
"exit" in perlport.
With the "PERL_VMS_POSIX_EXIT" logical name defined as
"ENABLE", setting $? will cause the new value to be encoded into
$^E so that either the original parent or child exit status values
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 it is known to not be a
valid native VMS status value. It is recommend that only values in the
range of normal Unix parent or child status numbers, 0 to 255 are used.
The pragma "use vmsish 'status'" makes $? reflect the actual VMS
exit status instead of the default emulation of POSIX status described
above. This pragma also disables the conversion of non-zero values to
SS$_ABORT when setting $? in an END block (but zero will still be
converted to SS$_NORMAL).
Do not use the pragma "use vmsish 'status'" with
"PERL_VMS_POSIX_EXIT" enabled, 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.
In general, with "PERL_VMS_POSIX_EXIT" enabled, more detailed
information will be available in the exit status for DCL scripts or other
native VMS tools, and will give the expected information for Posix
programs. It has not been made the default in order to preserve backward
compatibility.
N.B. Setting "DECC$FILENAME_UNIX_REPORT" implicitly enables
"PERL_VMS_POSIX_EXIT".
- $|
- Setting $| for an I/O stream causes data to be flushed all the way to disk
on each write ( i.e. not just to the underlying RMS buffers for a
file). In other words, it's equivalent to calling fflush() and
fsync() from C.
Standard modules with VMS-specific differences¶
SDBM_File¶
SDBM_File works properly on VMS. It has, however, one minor difference. The
database directory file created has a
.sdbm_dir extension rather than a
.dir extension.
.dir files are VMS filesystem directory files,
and using them for other purposes could cause unacceptable problems.
Revision date¶
Please see the git repository for revision history.
AUTHOR¶
Charles Bailey bailey@cor.newman.upenn.edu Craig Berry craigberry@mac.com Dan
Sugalski dan@sidhe.org John Malmberg wb8tyw@qsl.net