defined - Perl Documentation - Perldoc Browser
#defined EXPR #defined Returns a Boolean value telling whether EXPR has a value other than the undefined value undef.If EXPR is not present, $_ is checked. Many operations return undef to indicate failure, end of file, system error, uninitialized variable, and other exceptional conditions. This function allows you to distinguish undef from other values.
DA: 68 PA: 90 MOZ Rank: 58