Special Vars Quick Reference

$_	The default or implicit variable.
@_	Subroutine parameters.
$a $b	sort comparison routine variables.
@ARGV	The command-line args.
Regular Expressions
$<digit>	Regexp parenthetical capture holders.
$&	Last successful match (degrades performance).
${^MATCH}	Similar to $& without performance penalty. Requires /p modifier.
$`	Prematch for last successful match string (degrades performance).
${^PREMATCH}	Similar to $` without performance penalty. Requires /p modifier.
$'	Postmatch for last successful match string (degrades performance).
${^POSTMATCH}	Similar to $' without performance penalty. Requires /p modifier.
$+	Last paren match.
$^N	Last closed paren match (last submatch).
@+	Offsets of ends of successful submatches in scope.
@-	Offsets of starts of successful submatches in scope.
%+	Like @+, but for named submatches.
%-	Like @-, but for named submatches.
$^R	Last regexp (?{code}) result.
${^RE_DEBUG_FLAGS}	Current value of regexp debugging flags. See use re 'debug';
${^RE_TRIE_MAXBUF}	Control memory allocations for RE optimizations for large alternations.
Encoding
${^ENCODING}	The object reference to the Encode object, used to convert the source code to Unicode.
${^OPEN}	Internal use: \0 separated Input / Output layer information.
${^UNICODE}	Read-only Unicode settings.
${^UTF8CACHE}	State of the internal UTF-8 offset caching code.
${^UTF8LOCALE}	Indicates whether UTF8 locale was detected at startup.
IO and Separators
$.	Current line number (or record number) of most recent filehandle.
$/	Input record separator.
$|	Output autoflush. 1=autoflush, 0=default. Applies to currently selected handle.
$,	Output field separator (lists)
$\	Output record separator.
$"	Output list separator. (interpolated lists)
$;	Subscript separator. (Use a real multidimensional array instead.)
Formats
$%	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.
${^CHILD_ERROR_NATIVE}	Native status returned by the last pipe close, backtick (`` ) command, successful call to wait() or waitpid(), or from the system() operator.
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
$]	Old: Version and patch number of perl interpreter. Deprecated.
$^C	Current value of flag associated with -c switch.
$^D	Current value of debugging flags
$^F	Maximum system 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
${^WARNING_BITS}	Current set of warning checks enabled by use warnings;
$^X	Perl executable name.
${^GLOBAL_PHASE}	Current phase of the Perl interpreter.
$^H	Internal use only: Hook into Lexical Scoping.
%^H	Internaluse only: Useful to implement scoped pragmas.
${^TAINT}	Taint mode read-only flag.
${^WIN32_SLOPPY_STAT}	If true on Windows stat() won't try to open the file.
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.