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 differ-ently differently
ently 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 down-stream downstream
stream 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 avail-able available
able 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 exten-sion's extension's
sion'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 exten-sions extensions
sions 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 gen-erally generally
erally 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 gen-erate generate
erate 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 ver-sion version
sion of VMS prior to V7.1 you shouldn't nest the source directory too deeply in your directory struc-ture structure
ture 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 sev-eral several
eral 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 Extshort-name, Extshortname,
name, 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 pos-sible. possible.
sible. You may use either style, or both, on the command line and in scripts, but you may not com-bine combine
bine 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.
Filenames are, of course, still case-insensitive. For consistency, most Perl routines return file-specs filespecs
specs using lower case letters only, regardless of the case used in the arguments passed to them.
(This is true only when running under VMS; Perl respects the case-sensitivity of OSs like Unix.)
We've tried to minimize the dependence of Perl library modules on Unix syntax, but you may find that
some of these, as well as some scripts written for Unix systems, will require that you use Unix syn-tax, syntax,
tax, 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.
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 wild-card wildcard
card 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$spawn()
for asynchronous execution. You should be careful to close any pipes you have opened in a Perl
script, lest you leave any "orphaned" subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose output is used as the return value of
the expression. The string between the backticks is handled as if it were the argument to the "sys-tem" "system"
tem" operator (see below). In this case, Perl will wait for the subprocess to complete before con-tinuing. continuing.
tinuing.
The mailbox (MBX) that perl can create to communicate with a pipe defaults to a buffer size of 512.
The default buffer size is adjustable via the logical name PERL_MBX_SIZE provided that the value
falls between 128 and the SYSGEN parameter MAXBUF inclusive. For example, to double the MBX size
from the default within a Perl program, use "$ENV{'PERL_MBX_SIZE'} = 1024;" and then open and use
pipe constructs. An alternative would be to issue the command:
$ Define PERL_MBX_SIZE 1024
before running your wide record pipe program. A larger value may improve performance at the expense
of the BYTLM UAF quota.
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.
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 char-acter character
acter 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 asyn-chronous asynchronous
chronous 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.
-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 sys-tems, systems,
tems, 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, endpwent, eof, eval, exec*,
exists, exit, exp, fileno, getc, getlogin, getppid,
getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
grep, hex, import, index, int, join, keys, kill*,
last, lc, lcfirst, length, local, localtime, log, m//,
map, mkdir, my, next, no, oct, open, opendir, ord, pack,
pipe, pop, pos, print, printf, push, q//, qq//, qw//,
qx//*, quotemeta, rand, read, readdir, redo, ref, rename,
require, reset, return, reverse, rewinddir, rindex,
rmdir, s///, scalar, seek, seekdir, select(internal),
select (system call)*, setpwent, shift, sin, sleep,
sort, splice, split, sprintf, sqrt, srand, stat,
study, substr, 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, flock, fork*,
getpgrp, getpriority, getgrent, getgrgid,
getgrnam, setgrent, endgrent, ioctl, link, lstat,
msgctl, msgget, msgsend, msgrcv, readlink, semctl,
semget, semop, setpgrp, setpriority, shmctl, shmget,
shmread, shmwrite, socketpair, symlink, syscall
The following functions are available on Perls compiled with Dec C 5.2 or greater and running VMS 7.0
or greater:
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
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.
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 restor-ing restoring
ing 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 "bin-mode" "binmode"
mode" 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$hash_password" system service to generate the hashed represen-tation representation
tation of PLAINTEXT. If USER is a valid username, the algorithm and salt values are taken from
that user's UAF record. If it is not, then the preferred algorithm and a salt of 0 are used.
The quadword encrypted value is returned as an 8-character string.
The value returned by "crypt" may be compared against the encrypted password from the UAF
returned by the "getpw*" functions, in order to authenticate users. If you're going to do this,
remember that the encrypted password in the UAF was generated using uppercase username and pass-word password
word strings; you'll have to upcase the arguments to "crypt" to insure that you'll get the proper
value:
sub validate_passwd {
my($user,$passwd) = @_;
my($pwdhash);
if ( !($pwdhash = (getpwnam($user))[1]) ||
$pwdhash ne crypt("\U$passwd","\U$name") ) {
intruder_alert($name);
}
return 1;
}
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 begin-ning beginning
ning of the program. All other state of the program (e.g. values of variables, open file han-dles) handles)
dles) 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 neces-sary necessary
sary 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 mes-sage message
sage is printed, and "undef" is returned.
kill
In most cases, "kill" is implemented via the CRTL's "kill()" function, so it will behave accord-ing according
ing to that function's documentation. If you send a SIGKILL, however, the $DELPRC system service
is called directly. This insures that the target process is actually deleted, if at all possi-ble. possible.
ble. (The CRTL's "kill()" function is presently implemented via $FORCEX, which is ignored by
supervisor-mode images like DCL.)
Also, negative signal values don't do anything special under VMS; they're just converted to the
corresponding positive value.
qx//
See the entry on "backticks" above.
select (system call)
If Perl was not built with socket support, the system call version of "select" is not available
at all. If socket support is present, then the system call version of "select" functions only
for file descriptors attached to sockets. It will not provide information about regular files or
pipes, since the CRTL "select()" routine does not provide this functionality.
stat EXPR
Since VMS keeps track of files according to a different scheme than Unix, it's not really possi-ble possible
ble to represent the file's ID in the "st_dev" and "st_ino" fields of a "struct stat". Perl
tries its best, though, and the values it uses are pretty unlikely to be the same for two differ-ent different
ent files. We can't guarantee this, though, so caveat scriptor.
system LIST
The "system" operator creates a subprocess, and passes its arguments to the subprocess for execu-tion execution
tion as a DCL command. Since the subprocess is created directly via "lib$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 seman-tics semantics
tics unless the pragma "use vmsish 'status'" is in effect; see the description of $? in this doc-ument document
ument 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 subpro-cess subprocess
cess 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 $Config{'d_unlink_all_versions'} is "define",
then "unlink" will delete all versions of a file on the first call.)
"unlink" will delete a file if at all possible, even if it requires changing file protection
(though it won't try to change the protection of the parent directory). You can tell whether
you've got explicit delete access to a file by using the "VMS::Filespec::candelete" operator.
For instance, in order to delete only files to which you have delete access, you could say some-thing something
thing like
sub safe_unlink {
my($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 dis-tributed distributed
tributed 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.
utime LIST
Since ODS-2, the VMS file structure for disk files, does not keep track of access times, this
operator changes only the modification time of the file (VMS revision date).
waitpid PID,FLAGS
If PID is a subprocess started by a piped "open()" (see open), "waitpid" will wait for that sub-process, subprocess,
process, and return its final status value in $?. If PID is a subprocess created in some other
way (e.g. SPAWNed before Perl was invoked), "waitpid" will simply check once per second whether
the process has completed, and return when it has. (If PID specifies a process that isn't a sub-process subprocess
process of the current process, and you invoked Perl with the "-w" switch, a warning will be
issued.)
Returns PID on success, -1 on error. The FLAGS argument is ignored in all cases.
Perl variables
The following VMS-specific information applies to the indicated "special" Perl variables, in addition
to the general information in perlvar. Where there is a conflict, this information takes precedence.
%ENV
The operation of the %ENV array depends on the translation of the logical name PERL_ENV_TABLES.
If defined, it should be a search list, each element of which specifies a location for %ENV ele-ments. elements.
ments. If you tell Perl to read or set the element "$ENV{"name"}", then Perl uses the transla-tions translations
tions 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 signifi-cant significant
cant 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 run-ning running
ning 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 "envi-ron" "environ"
ron" 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 logi-cal logical
cal 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 zerolength
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()" func-tion.) function.)
tion.) 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 logicals
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 itera-tions iterations
tions 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 logicals representing process-permanent files, such as
"SYS$INPUT" and "SYS$OUTPUT". The translations for these logicals are prepended with a two-byte
binary value (0x1B 0x00) that needs to be stripped off if you want to use it. (In previous ver-sions versions
sions of Perl it wasn't possible to get the values of these logicals, 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 (NO-NAME-F-NOMSG), (NONAME-F-NOMSG),
NAME-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.
$? 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 are derived from the severity portion of the subprocess' exit status: 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 fatal error.
As a result, $? will always be zero if the subprocess' exit status indicated successful comple-tion, completion,
tion, and non-zero if a warning or error occurred. 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 $? to a non-zero value results in the generic fail-ure failure
ure status SS$_ABORT. See also "exit" in perlport.
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).
$| 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 direc-tory directory
tory files, and using them for other purposes could cause unacceptable problems.
Revision date
This document was last updated on 01-May-2002, for Perl 5, patchlevel 8.
AUTHOR
Charles Bailey bailey@cor.newman.upenn.edu Craig Berry craigberry@mac.com Dan Sugalski
dan@sidhe.org
perl v5.8.8 2006-01-07 PERLVMS(1)
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