title: External program call through java
body: <p>I want to run NS2(which is an external program in linux) commands through java, using ProcessBuilder
  when I get the ns command not found error</p>
  
  <pre><code>/home/maria/Documents/test.sh: line 4: ns: command not found
  Execution failed.
  org.apache.commons.exec.ExecuteException: Process exited with an error: 127 (Exit value: 127)
  at org.apache.commons.exec.DefaultExecutor.executeInternal(DefaultExecutor.java:404)
  at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:166)
  at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:153)
  at test.opencmd.runScript(opencmd.java:18)
  at test.opencmd.main(opencmd.java:30)
  </code></pre>
  
  <p>my java code is </p>
  
  <pre><code>package test;
  import java.io.*;
  public class test2 {
  public static void main(String args[]) {
  String s = null;
  try {
  // run the Unix "};
      //System.out.print(System.getProperty("user.home"));
      Process p = Runtime.getRuntime().exec( "ns /home/maria/ns-allinone-2.35/ns-2.35/indep-utils/cmu-scen-gen &amp;&amp; cbrgen.tcl -type cbr -nn 10 -seed 1 -mc 5 -rate 5.0");
  BufferedReader stdInput = new BufferedReader(new
  InputStreamReader(p.getInputStream()));
  BufferedReader stdError = new BufferedReader(new
  InputStreamReader(p.getErrorStream()));
  // read the output from the command
  System.out.println("Here is the standard output of the command:\n");
  while ((s = stdInput.readLine()) != null) {
  System.out.println(s);
  }
  // read any errors from the attempted command
  System.out.println("Here is the standard error of the command (if any):\n");
  while ((s = stdError.readLine()) != null) {
  System.out.println(s);
  }
  System.exit(0);
  }
  catch (IOException e) {
  System.out.println("exception happened - here's what I know: ");
  e.printStackTrace();
  System.exit(-1);
  }
  }
  }
  </code></pre>
  
  <p>I guess i am not making a right program call. </p>