Buffered Reader Outputting Runtime exec Commands

Question

Created this function to input unix commands and output the outputs of that unix command. But, I am having trouble with the unix commands I use. "ls" works to output the list of files, but if I do "ls -lart" it will output null. Having trouble further debugging or why this doesn't work. Code below.

private String[] unixCommand (String command, Boolean boolOutput) throws IOException, InterruptedException{
    Process run;
    int i = 0;
    String output = "";
    String[] finalOutput = new String[1000];
    sendToProcessView("Unix Command: " + command);
    run = Runtime.getRuntime().exec(command);
    run.waitFor();
    sendToProcessView("In Unix Command");
    if (boolOutput == true){        
        sendToProcessView("In Output Mode of Unix Command");
        BufferedReader stdInput = new BufferedReader(new InputStreamReader(run.getInputStream()));
        sendToProcessView("Passed Buffer Reader");
        while ((output = stdInput.readLine()) != null) {
            sendToProcessView("Output: " + output);
            finalOutput[i] = output;
            i++;
        }
    }
    return finalOutput;
}

Call run.waitFor() after you have consumed the command’s output, not before. — VGR
– VGR, Commented Jun 13, 2016 at 19:45
Found out that it will accept " ls " commands but wont take " ls Main* " commands with wildcard. — Devilishdil24
– Devilishdil24, Commented Jun 14, 2016 at 14:46
Runtime.getRuntime().exec(new String[] { "bash", "-c", myCommand }); — Devilishdil24
– Devilishdil24, Commented Jun 14, 2016 at 14:56

ControlAltDel · Accepted Answer · 2016-06-13 19:59:59Z

1

When interacting with the console, you should exec the console itself, and then use the Process input stream to send commands, eg (pseudocode - I'm not set up to test java code from my location, sorry)

sendToProcessView("Unix Command: " + command);
run = Runtime.getRuntime().exec("bash");
PrintStream in = new PrintStream(run.getOutputStream());
in.println("ls -lart");

You can then shut the process down by sending "exit" and reading the results the way you were, or using a threaded listener, like DataFetcher

edited Jun 13, 2016 at 19:59

answered Jun 13, 2016 at 19:22

ControlAltDel

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3 Comments

Devilishdil24 Over a year ago

PrintStream gave a constructor error and yea I agree that exiting the process is best practice, but did not fix the null issue.

ControlAltDel Over a year ago

I have fixed the code snippet - it is now run.getOutputStream() (was getInputStream())

Devilishdil24 Over a year ago

Sorry but not printing it out to the terminal. Returning the value back from the function.

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