Perl One-Liners

Appendix A. Perl’s Special Variables

In this appendix, I summarize Perl’s most commonly used special (predefined) variables, such as $_, $., $/, $\, $1, $2, $3 (and so on), $,, @F, and @ARGV, among others.

A.1 Variable $_

The $_ variable, called the default variable, is the most commonly used variable in Perl. Often this variable is pronounced “it” (when not pronounced “dollar-underscore”); as you read on, you’ll understand why.

When using the -n and -p command-line arguments, it’s (see?) where the input is stored. Also, many operators and functions act on it implicitly. Here’s an example:

perl -le '$_ = "foo"; print'

Here, I place the string "foo" in the $_ variable and then call print. When given no arguments, print prints the contents of the $_ ...