use Scalar::Util qw[ dualvar ];;

sub alwaysFails { return dualvar 0, 'Some text to explain the error'; };;

$rv = alwaysFails();;

print "Sub failed with error: $rv" if !$rv;;

##</code><code>##

print "Sub failed with error: $rv" if ! 0+$rv;;
Sub failed with error: Some text to explain the error

print "Sub failed with error: $rv" if ~$rv;;
Sub failed with error: Some text to explain the error

print "Sub failed with error: $rv" if $rv == 0;;
Sub failed with error: Some text to explain the error