#!/usr/local/bin/perl -w
use strict;

my @words = qw/
    beriberi
    coco
    couscous
    deed
    toot
    toto
    tutu
    assa
    saaa
    /;

for (@words) {
    print "$_\n"
        if /^(\w+)\1|(\w+)(\w+)\3\2$/
           # $x$x   | $x$y$y$x
}