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Apache Hadoop MapReduce Streaming
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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.streaming;

import java.util.Arrays;

import org.apache.hadoop.util.ToolRunner;

/** The main entry point. Usually invoked with the script 
 *  bin/hadoop jar hadoop-streaming.jar args.
 */
public class HadoopStreaming {

  public static void main(String[] args) throws Exception {
    if (args.length < 1) {
      System.err.println("No Arguments Given!");
      printUsage();
      System.exit(1);
    }
    int returnStatus = 0;
    String cmd = args[0];
    String[] remainingArgs = Arrays.copyOfRange(args, 1, args.length);
    if (cmd.equalsIgnoreCase("dumptb")) {
      DumpTypedBytes dumptb = new DumpTypedBytes();
      returnStatus = ToolRunner.run(dumptb, remainingArgs);
    } else if (cmd.equalsIgnoreCase("loadtb")) {
      LoadTypedBytes loadtb = new LoadTypedBytes();
      returnStatus = ToolRunner.run(loadtb, remainingArgs);
    } else if (cmd.equalsIgnoreCase("streamjob")) {
      StreamJob job = new StreamJob();
      returnStatus = ToolRunner.run(job, remainingArgs);
    } else { // for backward compatibility
      StreamJob job = new StreamJob();
      returnStatus = ToolRunner.run(job, args);
    }
    if (returnStatus != 0) {
      System.err.println("Streaming Command Failed!");
      System.exit(returnStatus);
    }
  }
  
  private static void printUsage() {
    System.out.println("Usage: mapred streaming [options]");
    System.out.println("Options:");
    System.out.println("  dumptb  Dumps all files that match the" 
        + " given pattern to ");
    System.out.println("                        standard output as typed " +
    		"bytes.");
    System.out.println("  loadtb  Reads typed bytes from standard input" +
        " and stores them in");
    System.out.println("                a sequence file in the specified path");
    System.out.println("  [streamjob]  Runs streaming job with given" +
        " arguments");
  }
}