Why Does Java's `Runtime.exec()` Produce Unexpected Results with Pipes?

Pipes and Runtime.exec() in Java

Consider the following Java code:

String commandf = "ls /etc | grep release";

try {
    Process child = Runtime.getRuntime().exec(commandf);
    child.waitFor();
    InputStream i = child.getInputStream();
    byte[] b = new byte[16];
    i.read(b, 0, b.length);
    System.out.println(new String(b));
} catch (IOException e) {
    e.printStackTrace();
    System.exit(-1);
}

The program's output is:

/etc:
adduser.co

However, when run from the shell, it correctly displays:

lsb-release

Cross-Platform Pipe Behavior

As mentioned in the question, pipe behavior is not cross-platform. The Java creators cannot guarantee that pipes will work consistently across different platforms.

Alternative Solutions

To address this issue, consider the following options:

• Execute a Script: Write a script that performs the desired command pipeline and execute the script instead of separate commands.
• Shell Execution: Use the sh command to execute the piped commands within the shell environment:

String[] cmd = {
  "/bin/sh",
  "-c",
  "ls /etc | grep release"
};

Process p = Runtime.getRuntime().exec(cmd);

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