Most programming languages have a native "Boolean" data type.  Perl
does not.

Perl has a simple and well known Truth System. The following scalar
values are false:

 @false = (undef, 0, 0.0, '', '0');

Every other scalar value is true.

This module provides basic Boolean support, by defining two special
objects: "true" and "false".

WWW: http://search.cpan.org/dist/boolean/