How to Use Pipes with Runtime.exec() in Java?

How can I enable piped commands using Runtime.exec() in Java?

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

Using pipes in Java can be tricky as the Runtime.exec() method does not handle shell-specific constructs like pipes by default. To make piping work, you need to execute each command separately and connect their input and output streams programmatically.

String command1 = "ls /etc";
String command2 = "grep release";

ProcessBuilder builder1 = new ProcessBuilder(command1.split(" ")).redirectErrorStream(true);
ProcessBuilder builder2 = new ProcessBuilder(command2.split(" ")).redirectErrorStream(true);

Process process1 = builder1.start();
Process process2 = builder2.start();

// Connect process1's output to process2's input
InputStream is = process1.getInputStream();
OutputStream os = process2.getOutputStream();
byte[] buffer = new byte[1024];
int bytesRead;
while((bytesRead = is.read(buffer)) != -1) {
    os.write(buffer, 0, bytesRead);
}

os.flush();
process1.waitFor();
process2.waitFor();

InputStream resultInputStream = process2.getInputStream();
while((bytesRead = resultInputStream.read(buffer)) != -1) {
    System.out.print(new String(buffer, 0, bytesRead));
}

Causes

• Java's Runtime.exec() does not recognize shell constructs such as pipes.
• Directly passing a piped command as a single string does not invoke a shell interpreter.

Solutions

• Split the command into individual commands and create separate processes.
• Connect the output stream of the first process to the input stream of the second process.

Mistake: Assuming that a single command string with pipes will execute correctly.

Solution: Use separate commands for each process and manually manage the input/output streams.

Mistake: Neglecting to handle I/O exhaustion that may occur when connecting streams.

Solution: Ensure that you read from the input stream completely or run them in separate threads.