Execution of WordCount Program

$ $HADOOP_HOME/bin/hadoop jar contrib/streaming/hadoop-streaming-1.
2.1.jar \
   -input input_dirs \ 
   -output output_dir \ 
   -mapper <path/mapper.py \ 
   -reducer <path/reducer.py

Where "\" is used for line continuation for clear readability.

For Example,

./bin/hadoop jar contrib/streaming/hadoop-streaming-1.2.1.jar 

 -input myinput -output myoutput -mapper  

/home/expert/hadoop-1.2.1/mapper.py -reducer  

/home/expert/hadoop-1.2.1/reducer.py