Perl Special Variables

Perl language defines some special variable, usually $, @, or% as a prefix, for example: $ _.

Many special variables have a very long English name, operating system variable $! Can be written as $ OS_ERROR.

If you want to use the English name of a special variable in the program need to head to adduse English;.This English special variables descriptive.

The most commonly used special variable $ _, the variable contains the default input and pattern matching content. Examples are as follows:

#!/usr/bin/perl

foreach ('Google','w3big','Taobao') {
	print $_;
	print "\n";
}

The above program, the output is:

Google
w3big
Taobao

The following example we do not use $ _ to output:

#!/usr/bin/perl

foreach ('Google','w3big','Taobao') {
	print;
	print "\n";
}

The above program, the output is:

Google
w3big
Taobao

Example, the first output "Google", then output "w3big", the final output "Taobao".

In the iteration loop, current loop of string in $ _ and then through the print output. Also print without specifying the output variable is used by default of $ _.

The following are a few states even without Perl will assume $ _ place:

• Monocular various functions, including as ord () and int () function, and so in addition to "-t" all file tests ( "-f", "- d"), "- t" default action STDIN.
• A list of the various functions, such as print () and unlink ().
• Do not use the "= ~" operator mode when the matching operation "m //", "s ///" and "tr ///".
• When other variables are not given "foreach" loop iteration variable default.
• Implicit iteration variable grep () and map () function.
• When "while" only only condition, and the condition is the result of "" operation test, $ _ is the default location for storing the input records. In addition to the "while" test conditions that would not happen. (Mnemonic: underline in a particular operation can be omitted.)

Special Variable Types

According to the special nature of the use of variables can be divided into the following categories:

• Special global scalar variable.

• Special global array variable.

• Hash special global variables.

• Global special file handle.

• Global special constant.

• Regex special variables.

• File handle special variables.

Special global scalar variable

Following is a list of all the special scalar variable containing special characters and English in the form of variables:

Special global array variable

Hash special global variables

Global special file handle

Global special constant

Regex special variables

/Version: (.*)|Revision: (.*)/ && ($rev = $+);

File handle special variables