javaapache-commons-exec

Unable to get output from Apache Commons Exec

Although the titles are very similar, this questions is NOT a duplicate of Process output from apache-commons exec.

I am trying to get the output of a command by using apache-commons exec. Here is what I am doing

import org.apache.commons.exec.*;
import java.io.ByteArrayOutputStream;

public class Sample {


    private static void runCommand(String cmd) throws Exception {
        ByteArrayOutputStream stdout = new ByteArrayOutputStream();
        PumpStreamHandler psh = new PumpStreamHandler(stdout);
        CommandLine cl = CommandLine.parse(cmd);
        DefaultExecutor exec = new DefaultExecutor();
        exec.setStreamHandler(psh);
        exec.execute(cl);
        System.out.println(stdout.toString());
    }

    public static void main(String... args) throws Exception {

        String cmd1 = "python -c \"print(10)\"";
        String cmd2 = "python -c \"import datetime; print(datetime.datetime.now())\"";

        runCommand(cmd1); // prints 10
        runCommand(cmd2); // should print the current datetime, but does not!
    }
}

The problem is that runCommand(cmd2) does not print anything to the output. When I try running the command on terminal, it works fine.

I have tried this program with and without the IDE so I'm sure this has nothing to do with the IDE console.

Here's a screenshot

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Here's a screenshot of the terminal

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Python command running on the terminal

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Solution

  • A colleague was able to come up with a solution to this problem. Changing

    CommandLine cl = CommandLine.parse(cmd);

    to 

    CommandLine cl = new CommandLine("/bin/sh");
cl.addArguments("-c");
cl.addArguments("'" + cmd + "'", false);

    solved the issue.

    The complete code looks as follows:

    import org.apache.commons.exec.*;
import java.io.ByteArrayOutputStream;

public class Sample {
    private static void runCommand(String cmd) throws Exception {
        ByteArrayOutputStream stdout = new ByteArrayOutputStream();
        PumpStreamHandler psh = new PumpStreamHandler(stdout);

        // CommandLine cl = CommandLine.parse(cmd);
        CommandLine cl = new CommandLine("/bin/sh");
        cl.addArguments("-c");
        cl.addArguments("'" + cmd + "'", false);

        DefaultExecutor exec = new DefaultExecutor();
        exec.setStreamHandler(psh);
        exec.execute(cl);
        System.out.println(stdout.toString());
    }

    public static void main(String[] args) throws Exception {
        String cmd1 =  "python -c \"print(10)\"";
        String cmd2 =  "python -c \"import datetime; print(datetime.datetime.now())\"";

        runCommand(cmd1); // prints 10
        runCommand(cmd2);
    }
}