Runtime.getRuntime().exec(“C:\cygwin\bin\bash.exe”) has no input to read

Question

I\'m trying to execute a new process and read from its input stream in Java. I have successfully used Runtime.getRuntime().exec(String) to start and receive input from sever

Answer 1

Regardless of Java, as far as I know you can pipe output (or input) from/to bash only when it is running as a script, not when it is running as an interactive shell (in which case you can only pass cmd parameters to it).

In other words, when you run bash from cmd as you mention in the comment, you see output, but it is contained in the bash process, it is not output that bash sends back to the parent cmd process.

Regarding the javac process, it is actually sending the output to the error stream. Try running from cmd javac 1>null and javac 2>null and you'll see the difference.
Have you looked at the api here? You can try to use ProcessBuilder and redirect the error stream back to the primary input stream, it'll be much easier to work with the processes this way.

Answer 2

A process typically has not only one but two output streams associated with it. These are:

1. stdout, which can be read with getInputStream()
2. stderr, which can be read with getErrorStream()

Javac writes to stderr, not stdout, so you don't read its output.

Because it is inconvenient to have to read both of them (Some years ago, I had to write an extra thread for this), they introduced a new API to system processes, namely the ProcessBuilder, which allows to redirect stderr to stdout.

Just replace the lines

    Process proc = Runtime.getRuntime().exec(command);
    InputStream in = proc.getInputStream();

with

    ProcessBuilder pb = new ProcessBuilder(command);
    pb.redirectErrorStream(true);
    Process proc = pb.start();

, add the required imports, and your test succeeds :).