#! perl -sw
use strict;
use FreezeThaw qw(cmpStr freeze);

sub asStr {
	return 'undef' if !defined $_[0];
	return "''" if $_[0] eq '';
	return '0' if $_[0] == 0;
	"$_[0]";
}

my @x = (0,1,'',undef);
my @y = (0,1,'',undef);

print '                  {$^W=0; ($x eq $y)', "\t", '!cmpStr($x,$y)', $/;
for my $x (@x) {
	for my $y (@y) {
		printf '%5s -v- %5s :', asStr($x), asStr($y);

		print "\t", do{local $^W=0;($x eq $y) ? 'Same' : 'Diff';};

		print "\t\t",!cmpStr($x,$y) ? 'Same' : 'Diff', $/;
	}
}

##</code><code>##

C:\test>test
                  {$^W=0; ($x eq $y)    !cmpStr($x,$y)
     0 -v-     0 :       Same            Same
     0 -v-     1 :       Diff            Diff
     0 -v-    '' :       Diff            Diff
     0 -v- undef :       Diff            Diff
     1 -v-     0 :       Diff            Diff
     1 -v-     1 :       Same            Same
     1 -v-    '' :       Diff            Diff
     1 -v- undef :       Diff            Diff
    '' -v-     0 :       Diff            Diff
    '' -v-     1 :       Diff            Diff
    '' -v-    '' :       Same            Same
    '' -v- undef :       Same            Diff # Here!
undef -v-     0 :       Diff            Diff
undef -v-     1 :       Diff            Diff
undef -v-    '' :       Same            Diff # Here!
undef -v- undef :       Same            Same

 1:13:29.67 C:\test>