Perl/Basics/Boolean Logic/Helper Natives

These helper natives are boolean statements that assist with the determination of the existence of or the defining of a variable.

exists

The exists native applies specifically to hashes and hash references.

print "This user has an age.\n" if exists $user->{'age'};

defined

The defined native determines if a scalar value is defined:

print "We received a response from the server.\n" if defined $response;

undef

The undef native determines if a scalar value is un-defined:

print "We received a response from the server.\n" unless undef $response;