Actually, bitwise-xor on strings and  tr/// (update: see Quote-Like Operators in perlop) go together quite nicely for something like this: 

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(pp);
 ;;
 for my $word (qw(Fool Foot Tool Toot Foal)) {
   my $diff = 'Fool' ^ $word;
   print qq{'$word': }, pp $diff;
   print qq{'Fool' and '$word' differ by 1 char}
     if 1 == $diff =~ tr/\x00//c;
   }
"
'Fool': "\0\0\0\0"
'Foot': "\0\0\0\30"
'Fool' and 'Foot' differ by 1 char
'Tool': "\22\0\0\0"
'Fool' and 'Tool' differ by 1 char
'Toot': "\22\0\0\30"
'Foal': "\0\0\16\0"
'Fool' and 'Foal' differ by 1 char

[download]

Update: Changed example code to use  tr/\x00//c (/c modifier: complement the search list).

Give a man a fish:  <%-{-{-{-<

In reply to Re^2: Comparing Lines within a Word List by AnomalousMonk
in thread Comparing Lines within a Word List by dominick_t

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