[TxMt] Problems printing with line numbers using TextMate bundle

I'm trying to teach myself the basics of programming -- I'm working with Python -- and one of the things I'm doing is going over extant scripts that I find useful to see how they do what they do. One of the scripts I'm interested in is pwyky, and so I wanted to print out the file but I need line numbers to help me keep track of where I am. No problem. Textmate has that in its eponymous bundle! But when I run it, I get the following dialogue error in the preview window:

sh: ps: command not found Received exception:TextMate::AppPathNotFoundException

I checked the first level code in the Bundle Editor, but this has to be somewhere in one of the Ruby scripts, but I am shy about digging in there. Any help would be appreciated.

john