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@genetics.upenn.edu.
+hesitate to drop a line to vmsperl@perl.org.
+
+=head1 Installation
+
+Directions for building and installing Perl 5 can be found in
+the file F<README.vms> in the main source directory of the
+Perl distribution..
=head1 Organization of Perl Images
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
-L<perlapi> for more details.) The Perl code for an
+L<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
C<use> or C<require> statement, and usually defines a Perl
tested creates several levels (at least 4) under the
directory in which the extension's source files live.
For this reason, you shouldn't nest the source directory
-too deeply in your directory structure, lest you eccedd RMS'
+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
during the build process for the Perl extension.
By default, the shareable image for an extension is placed
-in the F<[.Lib.Auto.I<Arch>.I<Extname>]> directory of the
+F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
F<VMS_AXP>, and I<Extname> is the name of the extension, with
-each C<::> translated to C<.>). However, it can be manually
-placed in any of several locations:
- - the F<[.Lib.Auto.I<Extname>]> subdirectory of one of
- the directories in C<@INC>, or
+each C<::> translated to C<.>). (See the MakeMaker documentation
+for more details on installation options for extensions.)
+However, it can be manually placed in any of several locations:
+ - the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
+ of one of the directories in C<@INC> (where I<PVers>
+ is the version of Perl you're using, as supplied in C<$]>,
+ with '.' converted to '_'), or
- one of the directories in C<@INC>, or
- a directory which the extensions Perl library module
passes to the DynaLoader when asking it to map
is the portion of the extension's name after the last C<::>, which
translates to the full file specification of the shareable image.
-=head1 Installation
-
-Directions for building and installing Perl 5 can be found in
-the file F<ReadMe.VMS> in the main source directory of the
-Perl distribution..
+=head1 File specifications
-=head1 File specifications
+=head2 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 fle
-specfication. Filenames are, of course, still case-
-insensitive. For consistency, most Perl routines return
-filespecs using lower case latters 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.)
+but you may not combine the two styles within a single file
+specification. VMS Perl interprets Unix pathnames in much
+the same way as the CRTL (I<e.g.> the first component of
+an absolute path is read as the device name for the
+VMS file specification). There are a set of functions
+provided in the C<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.)
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
+'/' is the directory separator, I<etc.> If you find instances
of this in the Perl distribution itself, please let us know,
so we can try to work around them.
-=head1 Command line redirection
-
-Perl for VMS supports redirection of input and output on the
-command line, using a subset of Bourne shell syntax:
- <F<file> reads stdin from F<file>,
- >F<file> writes stdout to F<file>,
- >>F<file> appends stdout to F<file>,
- 2>F<file> writes stderr to F<file>, and
- 2>>F<file> appends stderr to F<file>.
-
-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.
-
-=head1 Pipes
-
-Input and output pipes to Perl filehandles are supported; the
-"file name" is passed to lib$spawn() for asynchronous
-execution. You should be careful to close any pipes you have
-opened in a Perl script, lest you leave any "orphaned"
-subprocesses around when Perl exits.
-
-You may also use backticks to invoke a DCL subprocess, whose
-output is used as the return value of the expression. The
-string between the backticks is passed directly to lib$spawn
-as the command to execute. In this case, Perl will wait for
-the subprocess to complete before continuing.
-
-=head1 Wildcard expansion
+=head2 Wildcard expansion
File specifications containing wildcards are allowed both on
-the command line and within Perl globs (e.g. <C<*.c>>). If
+the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>). If
the wildcard filespec uses VMS syntax, the resultant
filespecs will follow VMS syntax; if a Unix-style filespec is
-passed in, Unix-style filespecs will be returned..
+passed in, Unix-style filespecs will be returned.
+In both cases, VMS wildcard expansion is performed. (csh-style
+wildcard expansion is available if you use C<File::Glob::glob>.)
If the wildcard filespec contains a device or directory
specification, then the resultant filespecs will also contain
a device and directory; otherwise, device and directory
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 the file version only
-if one was present in the input filespec.
+Similarly, the resultant filespec will contain the file version
+only if one was present in the input filespec.
+
+=head2 Pipes
+
+Input and output pipes to Perl filehandles are supported; the
+"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 C<system> operator (see below). In this case,
+Perl will wait for the subprocess to complete before continuing.
=head1 PERL5LIB and PERLLIB
-The PERL5LIB and PERLLIB logical names work as
-documented L<perl>, except that the element
-separator is '|' instead of ':'. The directory
-specifications may use either VMS or Unix syntax.
+The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
+except that the element separator is '|' instead of ':'. The
+directory specifications may use either VMS or Unix syntax.
+
+=head1 Command line
+
+=head2 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:
+
+=over
+
+=item *
+
+C<E<lt>file> reads stdin from C<file>,
+
+=item *
+
+C<E<gt>file> writes stdout to C<file>,
+
+=item *
+
+C<E<gt>E<gt>file> appends stdout to C<file>,
+
+=item *
+
+C<2E<gt>file> writes stderr to C<file>, and
+
+=item *
+
+C<2E<gt>E<gt>file> appends stderr to C<file>.
+
+=back
+
+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.
+
+=head2 Command line switches
+
+The following command line switches behave differently under
+VMS than described in L<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.
+
+=over 4
+
+=item -i
+
+If the C<-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.)
+
+=item -S
+
+If the C<-S> switch is present I<and> the script name does
+not contain a directory, then Perl translates the logical
+name DCL$PATH as a searchlist, using each translation as
+a directory in which to look for the script. In addition,
+if no file type is specified, Perl looks in each directory
+for a file matching the name specified, with a blank type,
+a type of F<.pl>, and a type of F<.com>, in that order.
+
+=item -u
+
+The C<-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.
+
+=back
=head1 Perl functions
Perl functions were implemented in the VMS port of Perl
(functions marked with * are discussed in more detail below):
- file tests*, abs, alarm, atan, binmode*, bless,
+ file tests*, abs, alarm, atan, backticks*, binmode*, bless,
caller, chdir, chmod, chown, chomp, chop, chr,
close, closedir, cos, crypt*, defined, delete,
- die, do, each, endpwent, eof, eval, exec*, exists,
- exit, exp, fileno, fork*, getc, getlogin, 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,
+ die, do, dump*, each, endpwent, eof, eval, exec*,
+ exists, exit, exp, fileno, fork*, getc, getlogin,
+ 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,
+ 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,
and calling them produces a fatal error (usually) or
undefined behavior (rarely, we hope):
- chroot, dbmclose, dbmopen, dump, fcntl, flock,
+ chroot, dbmclose, dbmopen, flock,
getpgrp, getppid, 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, truncate
+ 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,
getsockopt, listen, recv, select(system call)*,
send, setsockopt, shutdown, socket
+=over 4
=item File tests
specification without an explicit directory (e.g. C<DUA1:>), as
well as if passed a directory.
+Note: Some sites have reported problems when using the file-access
+tests (C<-r>, C<-w>, and C<-x>) on files accessed via DEC's DFS.
+Specifically, since DFS does not currently provide access to the
+extended file header of files on remote volumes, attempts to
+examine the ACL fail, and the file tests will return false,
+with C<$!> indicating that the file does not exist. You can
+use C<stat> on these files, since that checks UIC-based protection
+only, and then manually check the appropriate bits, as defined by
+your C compiler's F<stat.h>, in the mode value it returns, if you
+need an approximation of the file's protections.
+
+=item backticks
+
+Backticks create a subprocess, and pass the enclosed string
+to it for execution as a DCL command. Since the subprocess is
+created directly via C<lib$spawn()>, any valid DCL command string
+may be specified.
+
=item binmode FILEHANDLE
-The C<binmode> operator has no effect under VMS. It will
-return TRUE whenever called, but will not affect I/O
-operations on the filehandle given as its argument.
+The C<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 C<binmode>
+was called.
+
+Note that C<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
+C<vmsfopen> function in the VMS::Stdio extension to gain finer
+control of I/O to files and devices with different record structures.
=item crypt PLAINTEXT, USER
return 1;
}
+=item dump
+
+Rather than causing Perl to abort and dump core, the C<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
+C<dump>, or, if no label was specified, back to the
+beginning of the program. All other state of the program
+(I<e.g.> values of variables, open file handles) are not
+affected by calling C<dump>.
+
=item exec LIST
The C<exec> operator behaves in one of two different ways.
If the call to C<exec> does not follow a call to C<fork>, it
will cause Perl to exit, and to invoke the command given as
an argument to C<exec> via C<lib$do_command>. If the argument
-begins with a '$' (other than as part of a filespec), then it
+begins with '@' or '$' (other than as part of a filespec), then it
is executed as a DCL command. Otherwise, the first token on
the command line is treated as the filespec of an image to
run, and an attempt is made to invoke it (using F<.Exe> and
the process defaults to expand the filespec) and pass the
-rest of C<exec>'s argument to it as parameters.
+rest of C<exec>'s argument to it as parameters. If the token
+has no file type, and matches a file with null type, then an
+attempt is made to determine whether the file is an executable
+image which should be invoked using C<MCR> or a text file which
+should be passed to DCL as a command procedure.
You can use C<exec> in both ways within the same script, as
long as you call C<fork> and C<exec> in pairs. Perl
the subprocess before calling C<exec>.
In general, the use of C<fork> and C<exec> to create
-subprocess is not recommended under VMS; wherever possible,
+subprocesses is not recommended under VMS; wherever possible,
use the C<system> operator or piped filehandles instead.
=item getpwent
=item kill
-In most cases, C<kill> kill is implemented via the CRTL's C<kill()>
+In most cases, C<kill> is implemented via the CRTL's C<kill()>
function, so it will behave according to that function's
documentation. If you send a SIGKILL, however, the $DELPRC system
-service is is called directly. This insures that the target
+service is called directly. This insures that the target
process is actually deleted, if at all possible. (The CRTL's C<kill()>
function is presently implemented via $FORCEX, which is ignored by
supervisor-mode images like DCL.)
Also, negative signal values don't do anything special under
VMS; they're just converted to the corresponding positive value.
+=item qx//
+
+See the entry on C<backticks> above.
+
=item select (system call)
If Perl was not built with socket support, the system call
The C<system> operator creates a subprocess, and passes its
arguments to the subprocess for execution as a DCL command.
Since the subprocess is created directly via C<lib$spawn()>, any
-valid DCL command string may be specified. If LIST consists
-of the empty string, C<system> spawns an interactive DCL subprocess,
-in the same fashion as typiing B<SPAWN> at the DCL prompt.
+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. C<:> or C<]>), an attempt is made to expand it
+using a default type of F<.Exe> and the process defaults, and if
+successful, the resulting file is invoked via C<MCR>. This allows you
+to invoke an image directly simply by passing the file specification
+to C<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 C<MCR> or a text file which should be passed to DCL
+as a command procedure.
+
+If LIST consists of the empty string, C<system> spawns an
+interactive DCL subprocess, in the same fashion as typing
+B<SPAWN> at the DCL prompt.
+
Perl waits for the subprocess to complete before continuing
-execution in the current process.
+execution in the current process. As described in L<perlfunc>,
+the return value of C<system> is a fake "status" which follows
+POSIX semantics unless the pragma C<use vmsish 'status'> is in
+effect; see the description of C<$?> in this document for more
+detail.
+
+=item time
+
+The value returned by C<time> is the offset in seconds from
+01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order
+to make life easier for code coming in from the POSIX/Unix world.
=item times
according to the same rules the CRTL C<times()> routine.
Therefore, the "system time" elements will always be 0, since
there is no difference between "user time" and "system" time
-under VMS, and the time accumulated by subprocess may or may
+under VMS, and the time accumulated by a subprocess may or may
not appear separately in the "child time" field, depending on
whether L<times> keeps track of subprocesses separately. Note
especially that the VAXCRTL (at least) keeps track only of
subprocesses spawned using L<fork> and L<exec>; it will not
-accumulate the times of suprocesses spawned via pipes, L<system>,
+accumulate the times of subprocesses spawned via pipes, L<system>,
or backticks.
=item unlink LIST
C<unlink> will delete the highest version of a file only; in
order to delete all versions, you need to say
- 1 while (unlink LIST);
+
+ 1 while unlink LIST;
+
You may need to make this change to scripts written for a
Unix system which expect that after a call to C<unlink>,
no files with the names passed to C<unlink> will exist.
C<VMS::Filespec::candelete> operator. For instance, in order
to delete only files to which you have delete access, you could
say something like
+
sub safe_unlink {
my($file,$num);
foreach $file (@_) {
}
$num;
}
-Finally, if C<unlink> has to change the file protection to
-delete the file, and you interrupt it in midstream, the file
-may be left intact, but with a changed ACL allowing you delete
-access.
+
+(or you could just use C<VMS::Stdio::remove>, if you've installed
+the VMS::Stdio extension distributed with Perl). If C<unlink> has to
+change the file protection to delete the file, and you interrupt it
+in midstream, the file may be left intact, but with a changed ACL
+allowing you delete access.
=item utime LIST
=item waitpid PID,FLAGS
-If PID is a subprocess started by a piped L<open>, C<waitpid>
-will wait for that subprocess, and return its final
-status value. If PID is a subprocess created in some other way
-(e.g. SPAWNed before Perl was invoked), or is not a subprocess of
-the current process, C<waitpid> will check once per second whether
-the process has completed, and when it has, will return 0. (If PID
-specifies a process that isn't a subprocess of the current process,
-and you invoked Perl with the C<-w> switch, a warning will be issued.)
+If PID is a subprocess started by a piped C<open()> (see L<open>),
+C<waitpid> will wait for that subprocess, and return its final
+status value in C<$?>. If PID is a subprocess created in some other
+way (e.g. SPAWNed before Perl was invoked), or is not a subprocess
+of the current process, C<waitpid> will attempt to read from the
+process's termination mailbox, making the final status available in
+C<$?> when the process completes. If the process specified by PID
+has no termination mailbox, C<waitpid> will simply check once per
+second whether the process has completed, and return when it has.
+(If PID specifies a process that isn't a subprocess of the current
+process, and you invoked Perl with the C<-w> switch, a warning will
+be issued.)
-The FLAGS argument is ignored in all cases.
+Returns PID on success, -1 on error. The FLAGS argument is ignored
+in all cases.
+
+=back
=head1 Perl variables
+The following VMS-specific information applies to the indicated
+"special" Perl variables, in addition to the general information
+in L<perlvar>. Where there is a conflict, this information
+takes precedence.
+
+=over 4
+
=item %ENV
-Reading the elements of the %ENV array returns the
-translation of the logical name specified by the key,
-according to the normal search order of access modes and
-logical name tables. If you append a semicolon to the
-logical name, followed by an integer, that integer is
-used as the translation index for the logical name,
-so that you can look up successive values for search
-list logical names. For instance, if you say
+The operation of the C<%ENV> array depends on the translation
+of the logical name F<PERL_ENV_TABLES>. If defined, it should
+be a search list, each element of which specifies a location
+for C<%ENV> elements. If you tell Perl to read or set the
+element C<$ENV{>I<name>C<}>, then Perl uses the translations of
+F<PERL_ENV_TABLES> as follows:
- $ Define STORY once,upon,a,time,there,was
- $ perl -e "for ($i = 0; $i <= 6; $i++) " -
- _$ -e "{ print $ENV{'foo'.$i},' '}"
-
-Perl will print C<ONCE UPON A TIME THERE WAS>.
-
-The %ENV keys C<home>, C<path>,C<term>, and C<user>
-return the CRTL "environment variables" of the same
-names, if these logical names are not defined. The
-key C<default> returns the current default device
-and directory specification, regardless of whether
-there is a logical name DEFAULT defined..
-
-Setting an element of %ENV defines a supervisor-mode logical
-name in the process logical name table. C<Undef>ing or
-C<delete>ing an element of %ENV deletes the equivalent user-
-mode or supervisor-mode logical name from the process logical
-name table. If you use C<undef>, the %ENV element remains
-empty. If you use C<delete>, another attempt is made at
-logical name translation after the deletion, so an inner-mode
-logical name or a name in another logical name table will
-replace the logical name just deleted. It is not possible
-at present to define a search list logical name via %ENV.
+=over 4
+
+=item CRTL_ENV
+
+This string tells Perl to consult the CRTL's internal C<environ>
+array of key-value pairs, using I<name> as the key. In most cases,
+this contains only a few keys, but if Perl was invoked via the C
+C<exec[lv]e()> function, as is the case for CGI processing by some
+HTTP servers, then the C<environ> array may have been populated by
+the calling program.
+
+=item CLISYM_[LOCAL]
+
+A string beginning with C<CLISYM_>tells Perl to consult the CLI's
+symbol tables, using I<name> as the name of the symbol. When reading
+an element of C<%ENV>, the local symbol table is scanned first, followed
+by the global symbol table.. The characters following C<CLISYM_> are
+significant when an element of C<%ENV> is set or deleted: if the
+complete string is C<CLISYM_LOCAL>, the change is made in the local
+symbol table; otherwise the global symbol table is changed.
+
+=item Any other string
+
+If an element of F<PERL_ENV_TABLES> translates to any other string,
+that string is used as the name of a logical name table, which is
+consulted using I<name> as the logical name. The normal search
+order of access modes is used.
+
+=back
+
+F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
+you make while Perl is running do not affect the behavior of C<%ENV>.
+If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
+first the logical name tables specified by F<LNM$FILE_DEV>, and then
+the CRTL C<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.
-=item $?
+When an element of C<%ENV> is read, the locations to which
+F<PERL_ENV_TABLES> points are checked in order, and the value
+obtained from the first successful lookup is returned. If the
+name of the C<%ENV> element contains a semi-colon, it and
+any characters after it are removed. These are ignored when
+the CRTL C<environ> array or a CLI symbol table is consulted.
+However, the name is looked up in a logical name table, the
+suffix after the semi-colon is treated as the translation index
+to be used for the lookup. This lets you look up successive values
+for search list logical names. For instance, if you say
-Since VMS status values are 32 bits wide, the value of C<$?>
-is simply the final status value of the last subprocess to
-complete. This differs from the behavior of C<$?> under Unix,
-and under VMS' POSIX environment, in that the low-order 8 bits
-of C<$?> do not specify whether the process terminated normally
-or due to a signal, and you do not need to shift C<$?> 8 bits
-to the right in order to find the process' exit status.
+ $ Define STORY once,upon,a,time,there,was
+ $ perl -e "for ($i = 0; $i <= 6; $i++) " -
+ _$ -e "{ print $ENV{'story;'.$i},' '}"
+
+Perl will print C<ONCE UPON A TIME THERE WAS>, assuming, of course,
+that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
+is found, rather than a CLI symbol or CRTL C<environ> element with
+the same name.
+
+When an element of C<%ENV> is set to a defined string, the
+corresponding definition is made in the location to which the
+first translation of F<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 C<environ> values; they are set to the empty string.)
+An element of the CRTL C<environ> array can be set only if your
+copy of Perl knows about the CRTL's C<setenv()> function. (This is
+present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
+to see whether your copy of Perl was built with a CRTL that has this
+function.)
+
+When an element of C<%ENV> is set to C<undef>,
+the element is looked up as if it were being read, and if it is
+found, it is deleted. (An item "deleted" from the CRTL C<environ>
+array is set to the empty string; this can only be done if your
+copy of Perl knows about the CRTL C<setenv()> function.) Using
+C<delete> to remove an element from C<%ENV> has a similar effect,
+but after the element is deleted, another attempt is made to
+look up the element, so an inner-mode logical name or a name in
+another location will replace the logical name just deleted.
+In either case, only the first value found searching PERL_ENV_TABLES
+is altered. It is not possible at present to define a search list
+logical name via %ENV.
+
+The element C<$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 F<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} = $temp; # and define as logical name
+ }
+
+(You can't just say C<$ENV{$key} = $ENV{$key}>, since the
+Perl optimizer is smart enough to elide the expression.)
+
+Don't try to clear C<%ENV> by saying C<%ENV = ();>, it will throw
+a fatal error. This is equivalent to doing the following from DCL:
+
+ DELETE/LOGICAL *
+
+You can imagine how bad things would be if, for example, the SYS$MANAGER
+or SYS$SYSTEM logicals were deleted.
+
+At present, the first time you iterate over %ENV using
+C<keys>, or C<values>, you will incur a time penalty as all
+logical names are read, in order to fully populate %ENV.
+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 logicals representing process-permanent
+files, such as C<SYS$INPUT> and C<SYS$OUTPUT>. The translations for these
+logicals are prepended with a two-byte binary value (0x1B 0x00) that needs to be
+stripped off if you want to use it. (In previous versions of Perl it wasn't
+possible to get the values of these logicals, as the null byte acted as an
+end-of-string marker)
=item $!
VMS-specific errors. The numeric value of C<$!> is the
value of C<errno>, except if errno is EVMSERR, in which
case C<$!> contains the value of vaxc$errno. Setting C<$!>
-always sets errno to the value specified, and sets vaxc$errno
-to 4 (NONAME-F-NOMSG).
+always sets errno to the value specified. If this value is
+EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
+that the string value of C<$!> won't reflect the VMS error
+message from before C<$!> was set.
+
+=item $^E
+
+This variable provides direct access to VMS status values
+in vaxc$errno, which are often more specific than the
+generic Unix-style error messages in C<$!>. Its numeric value
+is the value of vaxc$errno, and its string value is the
+corresponding VMS message string, as retrieved by sys$getmsg().
+Setting C<$^E> sets vaxc$errno to the value specified.
+
+=item $?
+
+The "status value" returned in C<$?> 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 C<$?> are always 0 under VMS, since the
+termination status of a process may or may not have been
+generated by an exception. The next 8 bits are derived from
+the severity portion of the subprocess' exit status: if the
+severity was success or informational, these bits are all 0;
+if the severity was warning, they contain a value of 1; if the
+severity was error or fatal error, they contain the actual
+severity bits, which turns out to be a value of 2 for error
+and 4 for fatal error.
+
+As a result, C<$?> will always be zero if the subprocess' exit
+status indicated successful completion, and non-zero if a
+warning or error occurred. Conversely, when setting C<$?> in
+an END block, an attempt is made to convert the POSIX value
+into a native status intelligible to the operating system upon
+exiting Perl. What this boils down to is that setting C<$?>
+to zero results in the generic success value SS$_NORMAL, and
+setting C<$?> to a non-zero value results in the generic
+failure status SS$_ABORT. See also L<perlport/exit>.
+
+The pragma C<use vmsish 'status'> makes C<$?> reflect the actual
+VMS exit status instead of the default emulation of POSIX status
+described above. This pragma also disables the conversion of
+non-zero values to SS$_ABORT when setting C<$?> in an END
+block (but zero will still be converted to SS$_NORMAL).
+
+=item $|
+
+Setting C<$|> for an I/O stream causes data to be flushed
+all the way to disk on each write (I<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.
+
+=back
+
+=head1 Standard modules with VMS-specific differences
+
+=head2 SDBM_File
+
+SDBM_File works properly on VMS. It has, however, one minor
+difference. The database directory file created has a F<.sdbm_dir>
+extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
+directory files, and using them for other purposes could cause unacceptable
+problems.
=head1 Revision date
-This document was last updated on 16-Dec-1994, for Perl 5,
-patchlevel 2.
+This document was last updated on 2-Oct-2001, for Perl 5,
+patchlevel 8.
=head1 AUTHOR
-Charles Bailey bailey@genetics.upenn.edu
-
+Charles Bailey <bailey@cor.newman.upenn.edu>
+Craig Berry <craigberry@mac.com>
+Dan Sugalski <dan@sidhe.org>
https://perl5.git.perl.org / perl5.git / blobdiff