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2012-02-03

Perl Special Vars quick reference


source: Perl Monks
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.

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