Add ! command or equivalent to execute OS commands

I'm an old unix hacker, and whenever I am working in an environment with a specialized shell, I take advantage of the OS escape of a ! command. Could we implement that in the Roo shell, so if I'm trying to remember the name of a file, I can execute:

roo> !ls src/main/java/com/foo/bar
one two three
roo>

Maybe not super relevant but I thought it might be helpful and I can keep the number of shells down while I'm working.