Perl's special variables : Special Variables « Language Basics « Perl

Perl's special variables

VARIABLE DEFAULT VALUE DESCRIPTION

$_ N/A The default input and pattern-searching space.

$digit N/A Contains the subpattern from a successful parentheses pattern match.

$& N/A The string from the last successful pattern match.

$ N/A The preceding string to the last successful pattern match.

$' N/A The string following the last successful pattern match.

$+ N/A The last bracket matched from the last search pattern.

$* 0 Controls internal string multiline pattern matching.

$. N/A The current input line number of last filehandle read.

$/ \n The input record separator.

$| 0 If set to nonzero, forces a flush of the currently selected stream after every write.

$, N/A The output field separator for the print command.

$" Space The separator that joins elements of arrays interpolated in strings.

$\ N/A The output record separator for the print command.

$; \034 The subscript separator for multidimensional array emulation.

$# N/A The output format for printed numbers.

$% N/A The page number of the currently selected output stream.

$= 60 The page length of the currently selected output stream.

$ N/A The number of lines left on the current page.

$ filehandle The name of the current top of page format for the currently selected output stream.

$: \n- The characters used to fill a continuation field.

$L \f The default form-feed character.

$? N/A The status value returned from the last system, pipe close, or back tick command.

$! N/A Contains the current value of errno.

$@ N/A The Perl syntax error from the last eval statement.

$$ N/A The process ID (PID) of the current running Perl script.

$< N/A The real user ID (UID) of the current running process.

$> N/A The effective UID of the current running process.

$( N/A The real group ID (GID) of the current running process.

$) N/A The effective GID of the current running process.

$0 N/A The name of the file of the Perl script.

$[ 0 The index of the first element of an array.

$] N/A The string printed out when Perl is run with the -v command line option.

$A N/A The accumulator for form line and write operations.

$D N/A The current value of the debugging flags.

$F 2 The maximum number of system file descriptors.

$I N/A Contains the current value of the in-place editing flag (-i).

$P N/A Internal debugging flag.

$T N/A The time in which the script began running.

$W N/A The current value of the warning switch.

$X N/A The name of the Perl binary that was executed.

$ARGV N/A The name of the current file when reading from <>.

Related examples in the same category

1.	Special Literals
2.	Splitting up $_
3.	Splitting up $_ and creating an unnamed list
4.	The list separator is a comma
5.	The list separator is the empty string
6.	Passing Arguments at the Command Line
7.	Special Hashes: The %ENV Hash
8.	The %SIG hash sets signal handlers for signals.
9.	A program that changes the value of $/.
10.	A program that uses the $" (dollar and quotation) variable.
11.	A program that uses the $(dollar), variable.
12.	A program that uses the $< variable.
13.	A program that uses the $\(dollar and slash) variable.
14.	A simple program that assigns to $_ using .
15.	A simple version of the cat command using $_.
16.	ARGV and the Null Filehandle
17.	ARGV in Perl represents the command-line arguments.
18.	Aliases and Values
19.	Alternative names for Perl system variables.
20.	Assign elements in @_ to scalar
21.	Assign string array to @ARGV by using qw
22.	Assign value to @_
23.	Build the ARGV array with qw function
24.	@_ has runtime scope.
25.	A more expanded version for showing how to use the $_
26.	Built-in variables: $_
27.	Call-by-Reference and the @_ Array
28.	Capturing fatal errors
29.	Catching the sigINT signal
30.	Code the $_ specifically
31.	Compare value entered with number with underscore
32.	Error message is stored in $!
33.	Extracts information from the $] variable.
34.	$! is the error number
35.	$! stores the error message
36.	$" is the separator
37.	$# is the default format
38.	$(dollar), is the separator
39.	$MATCH = $&
40.	$SIG{__DIE__}
41.	$SIG{__WARN__} = 'IGNORE';
42.	$SIG{__WARN__} = sub {die "Warning: $_[0]"};
43.	$\ is 'END_OF_OUTPUT'
44.	$^ is the format header
45.	$^O stores the name of the operating system
46.	$^S: is inside eval
47.	$^W: Check the '-w switch'
48.	$^X: get the Perl execuatable file name
49.	$_ for print function
50.	$_ stores the user input
51.	$~ is the format
52.	%INC values
53.	File-searching program using $ARGV.
54.	Get Computer Name key in the %ENV
55.	Get local time from $^T
56.	If $_contains needle, the string is printed.
57.	Integer signal
58.	Lines Remaining on the Page: $-
59.	List all command line argument
60.	Local builtin var
61.	Locate all numbers less than 6
62.	Manipuate @_ and return @_
63.	Mannually change the $1 variable
64.	Match: $&
65.	Perl 5 Built-In Variables
66.	Perl's modules reside in the directories named in the @INC array, or subdirectories
67.	Perl's special arrays
68.	Postmatch $'
69.	Prematch: $`
70.	Print all command line argument
71.	Print the default variable's ($_) value
72.	Quick Sum
73.	Read and set environment variables?
74.	Read lines from supplied filenames
75.	Reference element in @_
76.	Resetting array base
77.	Retrieving the Entire Pattern: $&
78.	Saving in the $& special scalar
79.	Set the $/ and chomp
80.	Special Variables
81.	System variables that control how write sends output to a file
82.	Test of open and die with $!.
83.	The $_ Scalar Variable
84.	The @* field
85.	The @ISA Array and Calling Methods
86.	The Argument Vector @ARGV
87.	The Pattern-Matching Operator and $_
88.	The Substitution Operator and $_
89.	The code executes a line of code you type as long as that line doesn't start with a #
90.	The environment associative array: Associative arrays %ENV holds your system's environment variables.
91.	The following functions and operators work with the $_ variable by default:
92.	The shift operator returns an undefined value if the array has no more elements.
93.	To list all .pm files by using the @INC array
94.	Use while loop to display all entries in ENV
95.	Using $, to set the separator for print command
96.	Using $_ (dollar underscore)
97.	Using $_ as the array index
98.	Using $_ variable with while statement
99.	Using %SIG to define our own signal handlers
100.	Using @_ directly
101.	Using __LINE__ to output line number
102.	Using eof and <> together.
103.	Using the $. variable.
104.	Using the $;(dollar and semicolon) variable.
105.	Using the @_ to reference the parameter
106.	Using the Default Variable $_
107.	Using the diamond operator with @ARGV
108.	Using the if statement to check the command line parameters
109.	Using the special Perl variable $! in the message passed to die.
110.	Using tr to convert all file names passed in to uppercase
111.	Verify the total number of the command line parameter
112.	Working with $_ usually makes programming much easier, but more confusing to the uninitiated
113.	You display the current line of execution in a Perl script by referring to it with the __LINE__ token.
114.	You display the name of the current Perl package with __PACKAGE__.
115.	You display the name of the current file with the __FILE__ token
116.	foreach (@_)
117.	foreach loop and $_
118.	or die $!
119.	or die $^E;
120.	print "Hello, $ENV{USER}!\n";
121.	print $INC{'English.pm'};
122.	print $]; (Perl version number)
123.	print out all pm library location
124.	prints out each element of @ARGV separately
125.	shift: defaults to shifting @ARGV
126.	time - $^T
127.	undef $/;