Hadoop command line explanation

Question

Can some one explain me this syntax ,

bin/hadoop jar hadoop*examples*.jar wordcount /user/hpuser/testHadoop /user/hpuser/testHadoop-output

Why are we using jar soon after bin/hadoop What does hadoop*examples*.jar means..? Do wordcount is name of the job, or we asking hadoop to count no of words..?

http://www.michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-single-node-cluster/

Answer 1

Command Guide:

jar

Runs a jar file. Users can bundle their Map Reduce code in a jar file and execute it using this command.

Usage: hadoop jar <jar> [mainClass] args...

jar is the command. hadoop*examples*.jar is the jar file. WordCount is the main class. The rest are arguments passed to the WordCount.main() function:

public static void main(String[] args) throws Exception {
  int res = ToolRunner.run(new Configuration(), new WordCount(), args);
  System.exit(res);
}