PERLVMS(1) Perl Programmers Reference Guide PERLVMS(1)
NAME
perlvms - VMS-specific documentation for Perl
DESCRIPTION
Gathered below are notes describing details of Perl 5s 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 havent tried to duplicate com
plete 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 weve missed something you
think should appear here, please dont 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 youve 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 specifi
cation 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 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 com
mand 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
- its 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 configura
tion, the object code for the extension is linked directly into Perl
Shr.Exe, and is initialized whenever Perl is invoked. In the dynamic
configuration, the extensions machine code is placed into a separate
shareable image, which is mapped by Perls 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 extensions 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 "Make
Maker" 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,
youll 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
extensions name to the "ext" macro, and the extensions object file to
the "extobj" macro. Youll also need to build the extensions 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, youll need to copy the extensions 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 exten
sions source files live. For this reason if you are running a version
of VMS prior to V7.1 you shouldnt 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 cant place the files near the top
of the physical directory structure.)
VMS support for this process in the current release of Perl is suffi
cient 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:
the [.Lib.Auto.Arch$PVersExtname] subdirectory of one of the direc
tories in @INC (where PVers is the version of Perl youre 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 isnt in any of these places, youll need to
define a logical name Extshortname, where Extshortname is the portion
of the extensions 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 specifica
tion). 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 filespecs using lower case letters only,
regardless of the case used in the arguments passed to them. (This is
true only when running under VMS; Perl respects the case-sensitivity
of OSs like Unix.)
Weve 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.
Wildcard expansion
File specifications containing wildcards are allowed both on the com
mand line and within Perl globs (e.g. "<*.c>"). If the wildcard file
spec 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 direc
tory 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 resul
tant 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 direc
tory is Perl_Root:[000000], the expansion of "[.t]*.*" will yield file
specs 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$spawn() for asynchronous execution. You should
be careful to close any pipes you have opened in a Perl script, lest
you leave any "orphaned" subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose output is
used as the return value of the expression. The string between the
backticks is handled as if it were the argument to the "system" opera
tor (see below). In this case, Perl will wait for the subprocess to
complete before continuing.
The mailbox (MBX) that perl can create to communicate with a pipe
defaults to a buffer size of 512. The default buffer size is
adjustable via the logical name PERL_MBX_SIZE provided that the value
falls between 128 and the SYSGEN parameter MAXBUF inclusive. For exam
ple, to double the MBX size from the default within a Perl program, use
"$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" 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 com
mand 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 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 cre
ate a core dump file.
Perl functions
As of the time this document was last revised, the following Perl func
tions 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 call
ing 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 youve 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 protec
tions. Since real and effective UIC dont 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", arent 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 direc
tory.
Note: Some sites have reported problems when using the file-access
tests ("-r", "-w", and "-x") on files accessed via DECs DFS.
Specifically, since DFS does not currently provide access to the
extended file header of files on remote volumes, attempts to exam
ine the ACL fail, and the file tests will return false, with $!
indicating that the file does not exist. You can use "stat" on
these files, since that checks UIC-based protection only, and then
manually check the appropriate bits, as defined by your C com
pilers stat.h, in the mode value it returns, if you need an
approximation of the files protections.
backticks
Backticks create a subprocess, and pass the enclosed string to it
for execution as a DCL command. Since the subprocess is created
directly via "lib$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 filehan
dle. 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 "vms
fopen" 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$hash_password" system service to
generate the hashed representation of PLAINTEXT. If USER is a
valid username, the algorithm and salt values are taken from that
users UAF record. If it is not, then the preferred algorithm and
a salt of 0 are used. The quadword encrypted value is returned as
an 8-character string.
The value returned by "crypt" may be compared against the encrypted
password from the UAF returned by the "getpw*" functions, in order
to authenticate users. If youre going to do this, remember that
the encrypted password in the UAF was generated using uppercase
username and password strings; youll have to upcase the arguments
to "crypt" to insure that youll get the proper value:
sub validate_passwd {
my($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" opera
tor 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 argu
ment 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 com
mand 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 users 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_DIF
FERENTIAL is defined as the number of seconds which must be added
to UTC to yield local time. (This logical name is defined automat
ically if you are running a version of VMS with built-in UTC sup
port.) 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 CRTLs "kill()" func
tion, so it will behave according to that functions 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 possible. (The CRTLs "kill()" function is
presently implemented via $FORCEX, which is ignored by supervisor-
mode images like DCL.)
Also, negative signal values dont do anything special under VMS;
theyre just converted to the corresponding positive value.
qx//
See the entry on "backticks" above.
select (system call)
If Perl was not built with socket support, the system call version
of "select" is not available at all. If socket support is present,
then the system call version of "select" functions only for file
descriptors attached to sockets. It will not provide information
about regular files or pipes, since the CRTL "select()" routine
does not provide this functionality.
stat EXPR
Since VMS keeps track of files according to a different scheme than
Unix, its not really possible to represent the files ID in the
"st_dev" and "st_ino" fields of a "struct stat". Perl tries its
best, though, and the values it uses are pretty unlikely to be the
same for two different files. We cant guarantee this, though, so
caveat scriptor.
system LIST
The "system" operator creates a subprocess, and passes its argu
ments to the subprocess for execution as a DCL command. Since the
subprocess is created directly via "lib$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 speci
fication (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 "sys
tem", 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 com
mand procedure.
If LIST consists of the empty string, "system" spawns an interac
tive DCL subprocess, in the same fashion as typing SPAWN at the DCL
prompt.
Perl waits for the subprocess to complete before continuing execu
tion 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 CRTLs 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 "sys
tem time" elements will always be 0, since there is no difference
between "user time" and "system" time under VMS, and the time accu
mulated by a subprocess may or may not appear separately in the
"child time" field, depending on whether times keeps track of sub
processes 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 sys
tem 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 $Config{d_unlink_all_ver
sions} is "define", then "unlink" will delete all versions of a
file on the first call.)
"unlink" will delete a file if at all possible, even if it requires
changing file protection (though it wont try to change the protec
tion of the parent directory). You can tell whether youve got
explicit delete access to a file by using the "VMS::Filespec::can
delete" operator. For instance, in order to delete only files to
which you have delete access, you could say something like
sub safe_unlink {
my($file,$num);
foreach $file (@_) {
next unless VMS::Filespec::candelete($file);
$num += unlink $file;
}
$num;
}
(or you could just use "VMS::Stdio::remove", if youve 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.
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 subprocess, and return its final sta
tus value in $?. If PID is a subprocess created in some other way
(e.g. SPAWNed before Perl was invoked), "waitpid" will simply
check once per second whether the process has completed, and return
when it has. (If PID specifies a process that isnt a subprocess
of the current process, and you invoked Perl with the "-w" switch,
a warning will be issued.)
Returns PID on success, -1 on error. The FLAGS argument is ignored
in all cases.
Perl variables
The following VMS-specific information applies to the indicated "spe
cial" Perl variables, in addition to the general information in perl
var. Where there is a conflict, this information takes precedence.
%ENV
The operation of the %ENV array depends on the translation of the
logical name PERL_ENV_TABLES. If defined, it should be a search
list, each element of which specifies a location for %ENV elements.
If you tell Perl to read or set the element "$ENV{"name"}", then
Perl uses the translations of PERL_ENV_TABLES as follows:
CRTL_ENV
This string tells Perl to consult the CRTLs 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 pro
cessing 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
CLIs 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 char
acters 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 ta
ble, 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 correspond
ing definition is made in the location to which the first transla
tion 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 names
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 "envi
ron" array can be set only if your copy of Perl knows about the
CRTLs "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 Perls
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 envi
ron array to a subprocess which isnt started by fork/exec, or
isnt running a C program, you can "promote" them to logical names
in the current process, which will then be inherited by all subpro
cesses, 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 cant just say $ENV{$key} = $ENV{$key}, since the Perl opti
mizer is smart enough to elide the expression.)
Dont 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 iterations will
not reread logical names, so they wont be as slow, but they also
wont 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 trans
lations for these logicals are prepended with a two-byte binary
value (0x1B 0x00) that needs to be stripped off if you want to use
it. (In previous versions of Perl it wasnt 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 CRTLs 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 (NON
AME-F-NOMSG), so that the string value of $! wont 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 pro
cess 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 completion, 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 intelligi
ble 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.
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, its 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
This document was last updated on 01-May-2002, for Perl 5, patchlevel
8.
AUTHOR
Charles Bailey bailey@cor.newman.upenn.edu Craig Berry craig
berry@mac.com Dan Sugalski dan@sidhe.org
perl v5.8.8 2008-04-25 PERLVMS(1)
|
