Error when using linux grep command in java

Question

I'm trying to get the output of grep linux shell command in java by using process builder. But i got a stuck in this case. Please help me. Thank in advice!

    String[] args = new String[7];
    args[0] = "/bin/bash";
    args[1] = "-c";
    args[2] = "grep";
    args[3] = "-n";
    args[4] = "-e";
    args[5] = "KERNELVERSION";
    args[6] = kernelFilePath.trim();

ProcessBuilder pb;
    Process process = null;
    try {
        pb = new ProcessBuilder(args);
        pb = pb.directory(new File(directory));
        pb.inheritIO();
        pb.redirectOutput(ProcessBuilder.Redirect.INHERIT);
        pb.redirectError(ProcessBuilder.Redirect.INHERIT);
        process = pb.start();
        process.waitFor();
    } catch (IOException | InterruptedException e) {
        System.out.println("executeCmdWithOutput() exception : " + e.toString());
    } finally {
        if (process != null) {
            process.destroy();
        }
    }

==> Error:

Usage: grep [OPTION]... PATTERN [FILE]...

Try 'grep --help' for more information.

I tried the command in bash and it worked fine:

grep -n -e KERNELVERSION ..../Makefile

Full command must be passed as single argument to bash: args[2] = "grep -n -e KERNELVERSION " + kernelFilePath.trim(); — gudok
– gudok, Commented Nov 9, 2017 at 11:16

t00r · Accepted Answer · 2017-11-09 11:22:15Z

2

Have you tried change the args[2] as full command?

Also, you can use pgrep, it does not require you to use pipe.

answered Nov 9, 2017 at 11:22

t00r

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1 Comment

mhawke Over a year ago

How will pgrep help? It is for grepping for running processes, not for data in a file.

mhawke · Accepted Answer · 2017-11-09 12:05:16Z

0

You don't need to explicitly run /bin/bash in order to execute the grep process. Just call it directly and ProcessBuilder will run it:

String[] args = {"grep", "-n", "KERNELVERSION", kernelFilePath.trim()};

Also, you don't need to use the -e option, unless there are multiple patterns that you are searching for.

If you really wanted to run grep in /bin/bash:

String[] args = {"/bin/bash", "-c", "grep -n KERNELVERSION " + kernelFilePath.trim()};

passes a single argument to bash containing the full command and arguments to execute.

edited Nov 9, 2017 at 12:05

answered Nov 9, 2017 at 11:49

mhawke

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