Backticks create system calls

[calebhearth]

For example, mkdir should call out to the system with "mkdir" and capture/return whatever text is printed to STDOUT and raise with whatever is printed to STDERR.

[halogenandtoast]

I made system do exactly this. Which is not the same as ruby's system. I figured exec would do what system does. I don't know if we need the ruby functionality of exec (which replaces the running process with the exec).

[calebhearth]

Okay. Maybe I'll just add some tokenizer magic to make whatever look like a call to system, then.