Built-in variables: $_ : Special Variables « Language Basics « Perl

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Perl » Language Basics » Special Variables

Built-in variables: $_


   



$_ allows you to write minimalist Perl scripts: 



#!/usr/bin/perl -w



# This script prints out all

# files listed on the command line.

#

while (<>) {    # From <ARGV>

    print;  # Prints $_

}

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.	Call-by-Reference and the @_ Array
27.	Capturing fatal errors
28.	Catching the sigINT signal
29.	Code the $_ specifically
30.	Compare value entered with number with underscore
31.	Error message is stored in $!
32.	Extracts information from the $] variable.
33.	$! is the error number
34.	$! stores the error message
35.	$" is the separator
36.	$# is the default format
37.	$(dollar), is the separator
38.	$MATCH = $&
39.	$SIG{__DIE__}
40.	$SIG{__WARN__} = 'IGNORE';
41.	$SIG{__WARN__} = sub {die "Warning: $_[0]"};
42.	$\ is 'END_OF_OUTPUT'
43.	$^ is the format header
44.	$^O stores the name of the operating system
45.	$^S: is inside eval
46.	$^W: Check the '-w switch'
47.	$^X: get the Perl execuatable file name
48.	$_ for print function
49.	$_ stores the user input
50.	$~ is the format
51.	%INC values
52.	File-searching program using $ARGV.
53.	Get Computer Name key in the %ENV
54.	Get local time from $^T
55.	If $_contains needle, the string is printed.
56.	Integer signal
57.	Lines Remaining on the Page: $-
58.	List all command line argument
59.	Local builtin var
60.	Locate all numbers less than 6
61.	Manipuate @_ and return @_
62.	Mannually change the $1 variable
63.	Match: $&
64.	Perl 5 Built-In Variables
65.	Perl's modules reside in the directories named in the @INC array, or subdirectories
66.	Perl's special arrays
67.	Perl's special variables
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 $/;

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