The Substitution Operator and $_ : Special Variables « Language Basics « Perl






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The Substitution Operator and $_

   

The substitution operator uses the $_ variable if you do not specify a variable using =~. 

For example, the following statement replaces the first occurrence of abc in $_ with def: 

s/abc/def/;








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.Perl's special variables
69.Postmatch $'
70.Prematch: $`
71.Print all command line argument
72.Print the default variable's ($_) value
73.Quick Sum
74.Read and set environment variables?
75.Read lines from supplied filenames
76.Reference element in @_
77.Resetting array base
78.Retrieving the Entire Pattern: $&
79.Saving in the $& special scalar
80.Set the $/ and chomp
81.Special Variables
82.System variables that control how write sends output to a file
83.Test of open and die with $!.
84.The $_ Scalar Variable
85.The @* field
86.The @ISA Array and Calling Methods
87.The Argument Vector @ARGV
88.The Pattern-Matching 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 $/;