#!/usr/bin/perl

# rcwords.pl: print immediately adjacent repeated words once from input,
# even if they are repeated more than once,
# and print out these words along with the line number(s) that they appeared.

use English;
use diagnostics;

$prevword = '';
$n = 0;

while ($line = <>) {
  
    $n = $n + 1;

    $line =~ s/[[:punct:]]/ /g;

    $line = lc $line;

    @words = split /[[:space:]]+/, $line;

    foreach $word (@words) {

        if ($word ne '') {

            if ($word eq $prevword) {
                print " $n $word\n";
            }

            $prevword = $word;

        }
    }
}