Good solution! I couldn't help but golf it a little. :) 
#!/usr/bin/perl -w
use strict;

while (<DATA>) {
    print if (/([a-z])\1/i);
}

__DATA__
balloon
hello
world
foo
bar
perlmonks
merry
christmas

[download]

In reply to Re^2: Using regex to match double letters, and only double letters by kwaping
in thread Using regex to match double letters, and only double letters by Anonymous Monk

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