Question

I want my Java program to run the command echo "text" > /home/maxbester/test.txt on several Unix based systems.

My code looks like:

private static final Logger LOG = Logger.getLogger(MyClass.class);
public String run(String cmd)  {
    String res = null;
    InputStream is = null;
    try {
        final Runtime rt = Runtime.getRuntime();
        final Process p = rt.exec(cmd);
        int exitStatus = -1;
        try {
            exitStatus = p.waitFor();
        } catch (InterruptedException e) {
            L0G.error(e.getMessage(), e);
        }
        is = p.getInputStream();

        if (exitStatus == 0) {
            if (is != null && is.available() > 0) {
                StringWriter stringWriter = new StringWriter();
                IOUtils.copy(is, stringWriter);
                res = stringWriter.toString();
            } else {
                L0G.error("InputStream is not available!");
            }
        }
    } catch (SecurityException e) {
        L0G.error(e.getMessage(), e);
    } catch (IOException e) {
        L0G.error(e.getMessage(), e);
    }
    return res;
}

When cmd equals echo "text" > /home/maxbester/test.txt and the file test.txt exists, res contains "text" > /home/maxbester/test.txt (and not echo "text" > /home/maxbester/test.txt, the echo disapeared) and test.txt is empty. However the exit value is 0 (so it should have worked correctly).

I run manually echo "text" > /home/maxbester/test.txt. Nothing was returned and the exit value was also 0.

So what’s going wrong with the exec command?

Answer 1

If you want to write text to a file in Java, you should take a look at FileWriter instead of relying on shell-specific details such as stream redirection.