The simplest MR job consists of a mapper only. The input data is divided in several parts, every processed by an independent mapper, and the results are collected in one directory, one file per mapper.

#!/usr/bin/perl
 
package Mapper;
use Moose;
with 'Hadoop::Mapper';
 
sub map {
  my ($self, $key, $value, $context) = @_;
 
  $context->write($key, $value);
}
 
package Main;
use Hadoop::Runner;
 
my $runner = Hadoop::Runner->new(
  mapper => Mapper->new(),
  input_format => 'TextInputFormat',
  output_format => 'TextOutputFormat',
  output_compression => 0);
 
$runner->run();

The values input_format, output_format and output_compression could be left out, because they are all set to their default value.

Resulting script can be executed locally (not distributed) using

perl script.pl run input_directory output_directory

All files in input_directory are processes. The output_directory must not exist.

To check that your Hadoop environment works, try running a MR job on /home/straka/wiki/cs-text, which outputs only articles with names beginning with a (ignoring the case).