Getting command Input with runtime java

Question

Hello i try to get Input in java from this command: "ps aux | grep java" I use this code but not work:

        Process process = Runtime.getRuntime().exec("ps aux | grep java");
    InputStream stdin = process.getInputStream();
    InputStreamReader isr = new InputStreamReader(stdin);
    BufferedReader br = new BufferedReader(isr);

    String line = null;
    System.out.println("<OUTPUT>");

    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }

    System.out.println("</OUTPUT>");
    int exitVal = process.waitFor();
    System.out.println("Process exitValue: " + exitVal);

output in console: Process exitValue: 1 Any ideas?

Try printing the subprocess's stderr to see what's going wrong. — DaoWen
– DaoWen, Commented Nov 24, 2016 at 16:04
this is error: error: garbage option Usage: ps [options] Try 'ps --help <simple|list|output|threads|misc|all>' or 'ps --help <s|l|o|t|m|a>' for additional help text. For more details see ps(1). but why when i use this command in console i have good output? — Larry
– Larry, Commented Nov 24, 2016 at 16:13

DaoWen · Accepted Answer · 2016-11-24 16:20:03Z

2

When you pass a single string to Runtime.getRuntime().exec(), it expects a single command and its arguments, which are automatically tokenized. In other words, your code is equivalent to executing this command:

ps 'aux' '|' 'grep' 'java'

See how |, grep, and java are all being passed as arguments to ps? That's the problem.

I suggest using ProcessBuilder instead, and running your command via bash:

Process process = new ProcessBuilder().command("bash", "-c", "ps aux | grep java").start()

This is equivalent to the following command:

bash -c 'ps aux | grep java'

Now the bash subprocess handles the piping between ps and grep, so it should all work correctly.

You could do the same thing with Runtime.getRuntime().exec(), but ProcessBuilder is a newer, cleaner interface and thus should probably be preferred for new code. (ProcessBuilder is actually just relatively new, since it was added in JDK1.5, vs the exec() method being around since JDK1.0.)

answered Nov 24, 2016 at 16:20

DaoWen

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1 Comment

Larry Over a year ago

Thx for help :)

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