for (1..4){
  print "$_:  ";
  if ( ($str) = func($_) ) { # list assignment only false for empty list
    print "Success $str\n";
  } else {
    print "Error $Error::message";
  }
}
 
sub func {
  $Error::message="Wrong wrong wrong!!";
  goto "L".shift;
 L1:   return "";
 L2:   return 0;
 L3:   return undef;
 L4:   return;                 # blank returns empty list
}
__DATA__
1:  Success 
2:  Success 0
Use of uninitialized value $str in concatenation (.) or string at /tmp/tst2.pl line 4.
3:  Success 
4:  Error Wrong wrong wrong!!