I'm writing a Ruby script to run Lua code for TextMate. Using:
output = `lua #{filename}`
works when the file prints happily, but when an error occurs (e.g. a
syntax error in the file) the error message is printed to stderr (I
think) and 'escapes' my capture.

How/can I catch output to stderr from another system command? (I want
to use the output later, I just don't want it spat out at that point.)