$( The real gid of this process. If you are on a machine that supports membership in multiple groups simultaneously, gives a space separated list of groups you are in. The first number is the one returned by getgid() , and the subsequent ones by getgroups() , one of which may be the same as the first number. However, a value assigned to $( must be a single number used to set the real gid. So the value given by $( should not be assigned back to $( without being forced numeric, such as by adding

perlvar NAME DESCRIPTIONThe Syntax of Variable Names SPECIAL VARIABLESGeneral Variables Variables related to regular expressions Variables related to filehandles Error Variables Variables related to the interpreter state Deprecated and removed variables

$& The string matched by the last successful pattern match (not counting any matches hidden within a BLOCK or eval() enclosed by the current BLOCK). See Performance issues above for the serious performance implications of using this variable (even once) in your code. This variable is read-only and dynamically-scoped. Mnemonic: like & in some editors.

$% The current page number of the currently selected output channel. Mnemonic: % is page number in nroff.

$$ The process number of the Perl running this script. Though you can set this variable, doing so is generally discouraged, although it can be invaluable for some testing purposes. It will be reset automatically across fork() calls. Note for Linux and Debian GNU/kFreeBSD users: Before Perl v5.16.0 perl would emulate POSIX semantics on Linux systems using LinuxThreads, a partial implementation of POSIX Threads that has since been superseded by the Native POSIX Thread Library (NPTL). LinuxThread

$# $# was a variable that could be used to format printed numbers. After a deprecation cycle, its magic was removed in Perl v5.10.0 and using it now triggers a warning: $# is no longer supported. This is not the sigil you use in front of an array name to get the last index, like $#array . That's still how you get the last index of an array in Perl. The two have nothing to do with each other. Deprecated in Perl 5. Removed in Perl v5.10.0.

$" When an array or an array slice is interpolated into a double-quoted string or a similar context such as /.../ , its elements are separated by this value. Default is a space. For example, this: print "The array is: @array\n"; is equivalent to this: print "The array is: " . join($", @array) . "\n"; Mnemonic: works in double-quoted context.

$! When referenced, $! retrieves the current value of the C errno integer variable. If $! is assigned a numerical value, that value is stored in errno . When referenced as a string, $! yields the system error string corresponding to errno . Many system or library calls set errno if they fail, to indicate the cause of failure. They usually do not set errno to zero if they succeed. This means errno , hence $! , is meaningful only immediately after a failure: if (open my $fh, "<", $filename)