Running linux command in java

Question

I want to run "ls" command in java and my code is- Note:- I am using WINDOWS.

import java.io.IOException;

public class Example
{
    public void fn()
    {
        Runtime run = Runtime.getRuntime();  
        Process p = null;  
        String cmd = "ls"; 

        try {  
            p = run.exec(cmd);  

            p.getErrorStream();  
            p.waitFor();
        } catch (IOException | InterruptedException e) {  
            e.printStackTrace();  
            System.out.println("ERROR.RUNNING.CMD");  
        } finally {
            p.destroy();
        }
    }

    public static void main(String[] args) throws IOException
    {
        Example sp = new Example();
        sp.fn();
    }
}

but I am getting following error while running this code in eclipse-

java.io.IOException: Cannot run program "ls": CreateProcess error=2, The system cannot find the file specified
    at java.lang.ProcessBuilder.start(Unknown Source)
    at java.lang.Runtime.exec(Unknown Source)
    at java.lang.Runtime.exec(Unknown Source)
    at java.lang.Runtime.exec(Unknown Source)
    at Example.fn(Example.java:12)
    at Example.main(Example.java:28)
Caused by: java.io.IOException: CreateProcess error=2, The system cannot find the file specified
    at java.lang.ProcessImpl.create(Native Method)
    at java.lang.ProcessImpl.<init>(Unknown Source)
    at java.lang.ProcessImpl.start(Unknown Source)
    ... 6 more
Exception in thread "main" ERROR.RUNNING.CMD
java.lang.NullPointerException
    at Example.fn(Example.java:23)
    at Example.main(Example.java:28)

what needs to be corrected? what library, etc. should I add to execute this piece of code?

I want to run "ls" command in java Are you sure? Because if what you need is a listing of files on the system, this is one terrible way to do it for multiple reasons — Aaron
– Aaron, Commented Mar 7, 2017 at 16:23
Silly question, but you are running on Linux and the ls command works on there? — Steve Smith
– Steve Smith, Commented Mar 7, 2017 at 16:27
Basically, your program seems to be correct - I was able to execute it on my system (Arch Linux) without errors. — TuringTux
– TuringTux, Commented Mar 7, 2017 at 16:36

Andrii Abramov · Accepted Answer · 2017-03-07 16:26:03Z

4

If you want to run any command from Java ensure that executable of this file is present in PATH environment variable.

Or at least you have to set working directory to /usr/bin or similar.

One more solution is to use absolute path to executable, e.g.:

Runtime.getRuntime().exec("/usr/bin/ls");

But it is bad way to specify absolute path to any file.

Why don't you use File#listFiles()?

answered Mar 7, 2017 at 16:26

Andrii Abramov

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