c:\@Work\Perl\monks>perl -wMstrict -e
"my @TEST_VALUES = ('55a', 'a55');
 foreach my $i (@TEST_VALUES)
 {
   print qq{Calling TEST('$i') / };
   print qq{TEST return values = @{[ TEST($i) ]} \n\n};
 }
 ;;
 sub TEST
 {
   my $N = shift;
   local $SIG{__WARN__} = sub {
     print qq{(warn: N=$N -> };
     $N = 77;
     print qq{N=$N) / };
     };
   print qq{N=$N / N+0=}, $N + 0;
   print qq{ / N.''=}, $N.'', qq{\n};
   return $N, $N+0, $N.'';
 }
"
Calling TEST('55a') / (warn: N=55a -> N=77) / N=55a / N+0=55 / N.''=77
TEST return values = 77 55 77

Calling TEST('a55') / (warn: N=a55 -> N=77) / N=a55 / N+0=0 / N.''=77
TEST return values = 77 0 77