How to make pipes work with Runtime.exec()?

Write a script, and execute the script instead of separate commands.

Pipe is a part of the shell, so you can also do something like this:

String[] cmd = {"/bin/sh","-c","ls /etc | grep release"};Process p = Runtime.getRuntime().exec(cmd);

I ran into a similar problem in Linux, except it was "ps -ef | grep someprocess".
At least with "ls" you have a language-independent (albeit slower) Java replacement. Eg.:

File f = new File("C:\\");String[] files = f.listFiles(new File("/home/tihamer"));for (String file : files) {    if (file.matches(.*some.*)) { System.out.println(file); }}

With "ps", it's a bit harder, because Java doesn't seem to have an API for it.

I've heard that Sigar might be able to help us:https://support.hyperic.com/display/SIGAR/Home

The simplest solution, however, (as pointed out by Kaj) is to execute the piped command as a string array. Here is the full code:

try {    String line;    String[] cmd = { "/bin/sh", "-c", "ps -ef | grep export" };    Process p = Runtime.getRuntime().exec(cmd);    BufferedReader in =            new BufferedReader(new InputStreamReader(p.getInputStream()));    while ((line = in.readLine()) != null) {        System.out.println(line);     }    in.close();} catch (Exception ex) {    ex.printStackTrace();}

As to why the String array works with pipe, while a single string does not... it's one of the mysteries of the universe (especially if you haven't read the source code). I suspect that it's because when exec is given a single string, it parses it first (in a way that we don't like). In contrast, when exec is given a string array, it simply passes it on to the operating system without parsing it.

Actually, if we take time out of busy day and look at the source code(at http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/lang/Runtime.java#Runtime.exec%28java.lang.String%2Cjava.lang.String[]%2Cjava.io.File%29), we find that is exactly what is happening:

public Process  [More ...] exec(String command, String[] envp, File dir)           throws IOException {    if (command.length() == 0)        throw new IllegalArgumentException("Empty command");    StringTokenizer st = new StringTokenizer(command);    String[] cmdarray = new String[st.countTokens()];    for (int i = 0; st.hasMoreTokens(); i++)        cmdarray[i] = st.nextToken();    return exec(cmdarray, envp, dir);}

Create a Runtime to run each of the process. Get the OutputStream from the first Runtime and copy it into the InputStream from the second one.