Executing DOS commands from Java

Question

I'm trying to read a file from the user, in which each line is a DOS command, and run it (it's okay to assume the commands are legal), but when I give a command like echo hi, I get runtime exception error:

Exception in thread "main" java.io.IOException: Cannot run program "echo": CreateProcess error=2, The system cannot find the file specified

I'm trying to run the commands like this:

Runtime.getRuntime().exec(command);

where command = "echo hi". This does work for commands like regedit though, so it seems the runtime I'm getting is like the "run" window and not cmd. Is there a way to run these commands in DOS?

Answer 1

That's because echo is not an external executable command (i.e., there is no echo.exe file on your hard disk, unless you put it there yourself). It's an internal command of the shell.

You'll probably find that you need to execute something like:

cmd.exe /c echo hello

Answer 2

If you use the the Process class to execute OS commands, instead the Runtime.exec(), you can set the command folder using the directory method :

ProcessBuilder pb = new ProcessBuilder("echo", "hello");
//sets the running directory
pb.directory(new File("/path/to/echo/exec"));
//execute the process
Process p = pb.start();