How to access shell script output when it is executed from inside a Java code?

Question

I need to execute the following script from Java and be able to view the results on console. But the echo statements are not visible on console. After spending some time on the web I was able to understand that I need to take control of the input output streams to be able to do this. But I didn't get information that I need to make this possible.

I have posted the script and the Java statements below:

Script:

#!/bin/sh
echo "Hello World"
echo "$1 $2"
exit 0

Java Code:

List<String> command = new ArrayList<String>();
command.add("sh");
command.add("sript.sh");
command.add("Technopath007");
command.add("Dennis");
ProcessBuilder builder = new ProcessBuilder(command);
Process process = builder.start();
BufferedReader is = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line = "";
while ((line = is.readLine()) != null)
    System.out.println(line);       

The existing threads on the topic doesn't seem to work.

Please do let me know what I am missing here. Thanks in advance.

Answer 1

Use a BufferedReader

Something like this:

BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
string line = "";
while ((line = reader.readLine()) != null)
    System.out.println(line);
reader.Close();

Answer 2

Try this:

/** Execute a command where each parameter is in the string array. It is better to
 * do such a call this way because passing a single string to the java
 * Runtime.getRuntime().exec("single long string") method invokes StringTokenizer
 * to split the string into an array of strings and it does a poor job at it.
 *
 * I.e. The string:
 *    ksh -c "mkdir /tmp/test"
 *
 * is split thus:
 *
 *    ksh
 *    -c
 *    "mkdir
 *    /tmp/test"
 *
 * and then the shell interpreter complains about unmatched quotes.
 *
 * Returns a list which is whatever was put
 * on the stdout, followed by what was put on stderr.
 * @param exec the execution array, the first entry is the executable to run.
 * Don't forget that shell builtin command must be run within a shell.
 * @return The output list.
 */
public List executeExactCommand(String exec[])
{
    int exitCode   = 3;  // Assume we failed
    List execOutput = new ArrayList();

    String execCmd = "";
    int    i;

    for (i = 0; i < exec.length; ++i) {
        execCmd += (((i != 0) ? " " : "") + exec[i]);
    }

    try {
        Process p = Runtime.getRuntime().exec(exec);

        try {
            InputStream  is   = p.getInputStream();
            StringBuffer desc;
            int          chr = 0;

            while (chr >= 0) {
                desc = new StringBuffer(5192);
                chr  = is.read();

                for (i = 0; (i < 5192) && (chr >= 0) && (chr != '\n'); chr = is.read()) {
                    // Because of Bill Gates, everyone in the world has to
                    // process for a possible, useless, RETURN character.
                    if (chr != '\r') {
                        desc.append((char) chr);
                        ++i;
                    }
                }

                if ((chr >= 0) || (desc.length() != 0)) {
                    execOutput.add(desc.toString());
                }
            }

            is  = p.getErrorStream();
            chr = 0;

            while (chr >= 0) {
                desc = new StringBuffer(5192);
                chr  = is.read();

                for (i = 0; (i < 5192) && (chr >= 0) && (chr != '\n'); chr = is.read()) {
                    // Because of Bill Gates, everyone in the world has to
                    // process for a possible, useless, RETURN character.
                    if (chr != '\r') {
                        desc.append((char) chr);
                        ++i;
                    }
                }

                if ((chr >= 0) || (desc.length() != 0)) {
                    execOutput.add(desc.toString());
                }
            }

            exitCode = p.waitFor();

            if (withCommandTrace) {
                execOutput.add("execCmd = " + execCmd + " (" + exitCode + ")");
            }
        }
        catch (InterruptedException x) {
            System.err.println("Error command interupted, cmd='" + execCmd + "'");
            System.err.println("Caught: " + x);
            execOutput.add("Error command interupted, cmd='" + execCmd + "'");
            execOutput.add("" + exitCode);
        }
    }
    catch (IOException x) {
        // couldn't exec command
        System.err.println("Error executing command, command=" + execCmd);
        System.err.println("Caught: " + x);
        execOutput.add("Error executing command, cmd='" + execCmd + "'");
        execOutput.add("" + exitCode);
    }

    if (withCommandTrace) {
        for (i = 0; (execOutput != null) && (i < execOutput.size()); ++i) {
            System.out.println((String) execOutput.get(i));
        }
    }

    return execOutput;
}

You would call it using something like this:

List eachOutputLines = executeExactCommand(["bash", "-c", "ls -la /"]);