If you're looking for a way to catch any two words that differ by any single letter (e.g. report if input contains "fool/foot" and/or "foot/loot" and/or "loot/lout"), then it's a matter of building on Eily's idea using bitwise xor on pairs of strings that are the same length. Look at the elements of the array returned by the "split" statement, and if only one element of the array is non-zero, then the given pair of strings differ by only one character. (You'll want to organize your input into groups based on word length, and only do comparisons within each group.)

OTOH, if you're looking for words that contain a particular pair of characters, and differ only in terms of using one vs. the other of those two (e.g. you really just want "bare/base", etc., but not "foot/fool"), you would probably want to use a regex like this: 

#!/usr/bin/perl

use strict;
use warnings;

my @words = <DATA>;
chomp @words;

while ( @words >= 2 ) {
    my $model = my $regex = shift @words;
    if ( $regex =~ s/(.*?)[rs](.*?)/$1\[rs\]$2/ ) {
        my @hits = grep /^$regex$/, @words;
        if ( @hits ) {
            print join( " ", $model, "matches", @hits, "using", $regex
+, "\n" );
        }
    }
}

__DATA__
bare
mare
base
case
bust
burt
bent
sat
rat
bat
matter
mattes
pat

[download]
(update: fixed the "while" condition as per hippo's remark below -- also added anchors around $regex in the grep call, so that "bare" doesn't match "debased", etc.)

In reply to Re: Comparing Lines within a Word List by graff
in thread Comparing Lines within a Word List by dominick_t

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