perlvms

\s-1PERL_ENV_TABLES\s0 is translated once when Perl starts up; any changes you make while Perl is running do not affect the behavior of CW%ENV. If \s-1PERL_ENV_TABLES\s0 is not defined, then Perl defaults to consulting first the logical name tables specified by \s-1LNM$FILE_DEV\s0, and then the \s-1CRTL\s0 CWenviron array. In all operations on CW%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 CW%ENV is read, the locations to which \s-1PERL_ENV_TABLES\s0 points are checked in order, and the value obtained from the first successful lookup is returned. If the name of the CW%ENV element contains a semi-colon, it and any characters after it are removed. These are ignored when the \s-1CRTL\s0 CWenviron array or a \s-1CLI\s0 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 CWONCE UPON A TIME THERE WAS, assuming, of course, that \s-1PERL_ENV_TABLES\s0 is set up so that the logical name CWstory is found, rather than a \s-1CLI\s0 symbol or \s-1CRTL\s0 CWenviron element with the same name. When an element of CW%ENV is set to a defined string, the corresponding definition is made in the location to which the first translation of \s-1PERL_ENV_TABLES\s0 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 \s-1NUL\s0 (\s-1ASCII\s0 00) character, since a logical name cannot translate to a zero-length string. (This restriction does not apply to \s-1CLI\s0 symbols or \s-1CRTL\s0 CWenviron values; they are set to the empty string.) An element of the \s-1CRTL\s0 CWenviron array can be set only if your copy of Perl knows about the \s-1CRTL\s0's CWsetenv() function. (This is present only in some versions of the \s-1DECCRTL\s0; check CW$Config{d_setenv} to see whether your copy of Perl was built with a \s-1CRTL\s0 that has this function.) When an element of CW%ENV is set to CWundef, the element is looked up as if it were being read, and if it is found, it is deleted. (An item “deleted” from the \s-1CRTL\s0 CWenviron array is set to the empty string; this can only be done if your copy of Perl knows about the \s-1CRTL\s0 CWsetenv() function.) Using CWdelete to remove an element from CW%ENV has a similar effect, but after the element is deleted, another attempt is made to look up the element, so an inner-mode logical name or a name in another location will replace the logical name just deleted. In either case, only the first value found searching \s-1PERL_ENV_TABLES\s0 is altered. It is not possible at present to define a search list logical name via CW%ENV. The element CW$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 \s-1PERL_ENV_TABLES\s0. 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} = $temp; # and define as logical name } (You can't just say CW$ENV{$key} = $ENV{$key}, since the Perl optimizer is smart enough to elide the expression.) Don't try to clear CW%ENV by saying CW%ENV = ();, it will throw a fatal error. This is equivalent to doing the following from \s-1DCL:\s0 DELETE/LOGICAL * You can imagine how bad things would be if, for example, the \s-1SYS$MANAGER\s0 or \s-1SYS$SYSTEM\s0 logicals were deleted. At present, the first time you iterate over CW%ENV using CWkeys, or CWvalues, you will incur a time penalty as all logical names are read, in order to fully populate CW%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 CWSYS$INPUT and CWSYS$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)