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>