PERLVMS(1) Perl Programmers Reference Guide PERLVMS(1)
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 AT 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.autoArch.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:
o 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 $], with '.' converted to '_'), or
o one of the directories in @INC, or
o a directory which the extensions Perl library module passes to the
DynaLoader when asking it to map the shareable image, or
o Sys$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:
o "<file" reads stdin from "file",
o ">file" writes stdout to "file",
o ">>file" appends stdout to "file",
o "2>file" writes stderr to "file",
o "2>>file" appends stderr to "file", and
o "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 00) 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
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)
$! 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 AT cor.edu Craig Berry
craigberry AT mac.com Dan Sugalski dan AT sidhe.org John Malmberg
wb8tyw AT qsl.net
perl v5.16.3 2013-03-04 PERLVMS(1)
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