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Built-In Functions
Defined

  • The defined() function tests a variable for existance and returns a value of true or false

  • Typical variable existance testing uses might include

      $myScalar++ if ( defined $myScalar );
      @myList = ( 1..5 ) if ( ! defined @myList );
      %myHash = () if ( defined %myHash );

  • For subroutine names you can do runtime existance testing 
      if ( defined &mySub ) {
	&mySub( "Yippee!" );
} else {
	die( "Darn!" );
}