run interactive command line application from java

Question

I normally use java.lang.ProcessBuilder and java.lang.Process to run external command line programs, and it works fine for run-and-done commands. For example, this would run "myProgram" with argument "myArg" in the working directory:

List<String> commandLine = new ArrayList<String>();
commandLine.add("myProgram");
commandLine.add("myArg");
ProcessBuilder builder = new ProcessBuilder(commandLine);
builder.redirectErrorStream(true);
Process process = builder.start();

However, say I wanted to run a script or program or something that had interactive input (it prompted me for more input after starting). Can I do that in Java with code similar to that above, or do I need a different approach? Or is there some library that can help me with this?

Answer 1

According to the documentation you should be able to redirect the input and output streams. This tells it to use the System.in/System.out from the parent process:

builder.redirectInput(ProcessBuilder.Redirect.INHERIT);
builder.redirectOutput(ProcessBuilder.Redirect.INHERIT);

If you want to write things to the processes's input:

If the source is Redirect.PIPE (the initial value), then the standard input of a subprocess can be written to using the output stream returned by Process.getOutputStream(). If the source is set to any other value, then Process.getOutputStream() will return a null output stream.

• 11684: with stdin and stdout you mean System.in and System.out?
• Christopher Schultz: I used this (including redirecting the error stream) to launch /usr/bin/vi from a Java command-line program and it behaved exactly as I had hoped.
• Enerccio: this is absolutely WRONG answer because this NOT opens interactive pseudo terminal this it is useless because child will buffer thus prevent ANY interaction.

Answer 2

Redirecting stdin and stdout is certainly one option for simple command-line programs.

Using a "robot" class is another, if you actually need to script keystrokes (for example, in a test script):

• http://www.java-tips.org/java-se-tips/java.awt/how-to-use-robot-class-in-java.html

• http://download.java.net/jdk7/archive/b123/docs/api/java/awt/Robot.html

Writing a simple .bat file or shell script, that calls your Java program and uses "<" and ">" redirection operators is yet a third option.

It all depends on exactly what you're looking for :)

• smcg: I basically want to force through confirmation prompts for a program that doesn't have a --force flag or equivalent.
• paulsm4: Can you run the program in a shell script? If "yes", would that be sufficient?
• paulsm4: @smcg - As I said, "It all depends on exactly what you're looking for :)". I just wanted to make sure you had all available answers. Good luck! Sincerely .. PSM
• 11684: with stdin and stdout you mean System.in and System.out?