Special Vars Quick Reference

$_	The default or implicit variable.
@_	Subroutine parameters.
$a $b	sort comparison routine variables.
Regular Expressions
$<digit>	Regexp parenthetical capture holders.
$&	Last successful match (degrades performance).
$`	Prematch for last successful match string (degrades performance).
$'	Postmatch for last successful match string (degrades performance).
$+	Last paren match.
$^N	Last closed paren match.
@+	Offsets of ends of successful submatches in scope.
@-	Offsets of starts of successful submatches in scope.
$*	Boolean for multi-line matching. Deprecated. Use /s and /m.
$^R	Last regexp (?{code}) result.
IO and Separators
$.	Current line number (or record number) of most recent filehandle.
$/	Input record separator.
$|	Output autoflush. 1=autoflush, 0=default
$,	Output field separator (lists)
$\	Output record separator.
$"	Output list separator. (interpolated lists)
$;	Subscript separator. (Use a real multidimensional array instead.)
Formats
$#	Output format for printed numbers (deprecated).
$%	Page number for currently selected output channel.
$=	Current page length.
$-	Number of lines left on page.
$~	Format name.
$^	Name of top-of-page format.
$:	Format line break characters
$^L	Form feed (default "\f").
$^A	Format Accumulator
Status Reporting
$?	Child error. Status code of most recent system call or pipe.
$!	Operating System Error. (What just went 'bang'?)
%!	Error number hash
$^E	Extended Operating System Error (Extra error explanation).
$@	Eval error.
ID's and Process Information
$$	Process ID
$<	Real user id of process.
$>	Effective user id of process.
$(	Real group id of process.
$)	Effective group id of process.
$0	Program name.
$^O	Operating System name.
Perl Status Info
$]	Version and patch number of perl interpreter.
$^C	Current value of flag associated with -c switch.
$^D	Current value of debugging flags
$^F	Maximum file descriptor.
$^I	Value of the -i (inplace edit) switch.
$^M	Emergency Memory pool.
$^P	Internal variable for debugging support.
$^R	Last regexp (?{code}) result.
$^S	Exceptions being caught. (eval)
$^T	Base time of program start.
$^V	Perl version.
$^W	Status of -w switch
$^X	Perl executable name.
Command Line Args
ARGV	Filehandle iterates over files from command line (see also <>).
$ARGV	Name of current file when reading <>
@ARGV	List of command line args.
ARGVOUT	Output filehandle for -i switch
Miscellaneous
@F	Autosplit (-a mode) recipient.
@INC	List of library paths.
%INC	Keys are filenames, values are paths to modules included via use, require, or do.
%ENV	Hash containing current environment variables
%SIG	Signal handlers.
$[	Array and substr first element (Deprecated!).

See perlvar for detailed descriptions of each of these (and a few more) special variables.

When modifiying special variables, it is often a good practice to localize the effects of the change. ie,

my @array = ( 1, 2, 3, 4, 5 );
print "@array\n";
{
    local $" = "\t";
    print "@array\n";
}
print "@array\n";
[download]

And the output.....

1 2 3 4 5
1       2       3       4       5       
1 2 3 4 5
[download]

The purpose of this node is to provide a super-concise categorized quick crossreference to Perl's special variables. perlvar provides a list in asciibetical order but doesn't really put the variables into easy to find categories.