How to invoke a Linux shell command from Java

exec does not execute a command in your shell

try

Process p = Runtime.getRuntime().exec(new String[]{"csh","-c","cat /home/narek/pk.txt"});

instead.

EDIT::I don't have csh on my system so I used bash instead. The following worked for me

Process p = Runtime.getRuntime().exec(new String[]{"bash","-c","ls /home/XXX"});

Use ProcessBuilder to separate commands and arguments instead of spaces. This should work regardless of shell used:

import java.io.BufferedReader;import java.io.File;import java.io.IOException;import java.io.InputStreamReader;import java.util.ArrayList;import java.util.List;public class Test {    public static void main(final String[] args) throws IOException, InterruptedException {        //Build command         List<String> commands = new ArrayList<String>();        commands.add("/bin/cat");        //Add arguments        commands.add("/home/narek/pk.txt");        System.out.println(commands);        //Run macro on target        ProcessBuilder pb = new ProcessBuilder(commands);        pb.directory(new File("/home/narek"));        pb.redirectErrorStream(true);        Process process = pb.start();        //Read output        StringBuilder out = new StringBuilder();        BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));        String line = null, previous = null;        while ((line = br.readLine()) != null)            if (!line.equals(previous)) {                previous = line;                out.append(line).append('\n');                System.out.println(line);            }        //Check result        if (process.waitFor() == 0) {            System.out.println("Success!");            System.exit(0);        }        //Abnormal termination: Log command parameters and output and throw ExecutionException        System.err.println(commands);        System.err.println(out.toString());        System.exit(1);    }}

Building on @Tim's example to make a self-contained method:

import java.io.BufferedReader;import java.io.File;import java.io.InputStreamReader;import java.util.ArrayList;public class Shell {    /** Returns null if it failed for some reason.     */    public static ArrayList<String> command(final String cmdline,    final String directory) {        try {            Process process =                 new ProcessBuilder(new String[] {"bash", "-c", cmdline})                    .redirectErrorStream(true)                    .directory(new File(directory))                    .start();            ArrayList<String> output = new ArrayList<String>();            BufferedReader br = new BufferedReader(                new InputStreamReader(process.getInputStream()));            String line = null;            while ( (line = br.readLine()) != null )                output.add(line);            //There should really be a timeout here.            if (0 != process.waitFor())                return null;            return output;        } catch (Exception e) {            //Warning: doing this is no good in high quality applications.            //Instead, present appropriate error messages to the user.            //But it's perfectly fine for prototyping.            return null;        }    }    public static void main(String[] args) {        test("which bash");        test("find . -type f -printf '%T@\\\\t%p\\\\n' "            + "| sort -n | cut -f 2- | "            + "sed -e 's/ /\\\\\\\\ /g' | xargs ls -halt");    }    static void test(String cmdline) {        ArrayList<String> output = command(cmdline, ".");        if (null == output)            System.out.println("\n\n\t\tCOMMAND FAILED: " + cmdline);        else            for (String line : output)                System.out.println(line);    }}

(The test example is a command that lists all files in a directory and its subdirectories, recursively, in chronological order.)

By the way, if somebody can tell me why I need four and eight backslashes there, instead of two and four, I can learn something. There is one more level of unescaping happening than what I am counting.

Edit: Just tried this same code on Linux, and there it turns out that I need half as many backslashes in the test command! (That is: the expected number of two and four.) Now it's no longer just weird, it's a portability problem.