For a similar library with a slightly different take, check out plumbum:

http://plumbum.readthedocs.org/en/latest/index.html

Here's the explanation on the differences:

"The project has been inspired by PBS of Andrew Moffat, and has borrowed some of his ideas (namely treating programs like functions and the nice trick for importing commands). However, I felt there was too much magic going on in PBS, and that the syntax wasn’t what I had in mind when I came to write shell-like programs. I contacted Andrew about these issues, but he wanted to keep PBS this way. Other than that, the two libraries go in different directions, where Plumbum attempts to provide a more wholesome approach."