MRJob is a Python package that helps you write and run Hadoop Streaming jobs. Here's a simple example:

$```$python

from mrjob.job import MRJob

class MRWordFrequencyCount$($MRJob$)$:

def mapper$($self$,\_,$ line$)$:

words $=$ line.split$()$

for word in words:

yield $($word$,1)$

def reducer$($self$,$ key, values$)$:

yield $($key$,$ sum$($values$))$

if $\_\_$name$\_\_==\text{'}\_\_$main$\_\_\text{'}$:

MRWordFrequencyCount.run$()$

$```$

This is a simple MapReduce job that counts the frequency of words. To run this script on multiple input files, you would use the command line like so:

$```$bash

python mrjob$\_$script.py input$1.$txt input$2.$txt input$3.$txt

$```$

Or$,$ to run it on all files in a directory:

$```$bash

python mrjob$\_$script.py directory$/*$

$```$

This will process all the files in the specified directories. The input files are specified as arguments when running the MRJob script.

Please replace $`$mrjob$\_$script.py$`$ with the name of your Python script, and $`$input$1.$txt$`,`$input$2.$txt$`,`$input$3.$txt$`,$ and $`$directory$/*`$ with your actual file names or directories.