Question

When i apply command command i do not get any output. How can i get output while using command or not both case?

public class test 
{

  public static void main(String args[])
  {
    System.out.println(
        systemtest("ifconfig | awk 'BEGIN { FS = \"\n\"; RS = \"\" } { print $1 $2 }' | sed -e 's/ .*inet addr:/,/' -e 's/ .*//'"));   

  }

  public static String systemtest(String cmds)
  {
    String value = "";
    try 
    { 
      String cmd[] = {
        "/bin/sh",
        "-c",
        cmds
      };       
      Process p=Runtime.getRuntime().exec(cmd); 
      // Try 0: here? wrong
      //p.waitFor(); 
      BufferedReader reader=new BufferedReader(new InputStreamReader(p.getInputStream())); 
      String line=reader.readLine(); 
      // Try 1: here?
      //p.waitFor(); 
      while(line!=null) 
      { 
        value += line + "\n";
        line=reader.readLine(); 
      } 
      // Try 2: here?
      p.waitFor(); 
    } catch(IOException e1) {

    } catch(InterruptedException e2) {

    } 

    return value;
  }

Answer 1

You need to read the output from the command before you call p.waitFor().

Facts:

• Output from an external command is delivered via an OS-level “pipe”.
• Pipes have a limited amount of buffering.
• If some producer process tries to write to a pipe that is “full”, the process is forced to wait until the consumer process has read some data from the pipe.

It is not hard to see (from the above facts) that the way that you’re application is written will result in a deadlock if the external application produces more output than can fit into the pipe’s buffer (in O/S space).

(Even if this is not the real cause of your problem this time, it could be other times. Watch out for deadlocks when reading from / writing to external processes.)