A Perl Word Count reducer script. Can be used as a reducer in Hadoop using the Streaming interface. Tested with Java 1.6 and Hadoop 1.0.4.

wc_reducer.pl

#!/usr/bin/env perl

use warnings;
use strict;

my $current_word = "";
my $current_count = 0;

while (<>) {
    chomp;

    my ($word, $count) = split /\t/;

    if ($word eq $current_word) {
        $current_count += $count;
    } else {
        print "$current_word\t$current_count\n" if length($current_word);
        $current_word = $word;
        $current_count = $count;
    }
}

print "$current_word\t$current_count\n";