Raise exception on shell command failure?

Question

I'm writing some scripts in Ruby, and I need to interface with some non-Ruby code via shell commands. I know there are at least 6 different ways of executing shell commands from Ruby, unfortunately, none of these seem to stop execution when a shell command fails.

Basically, I'm looking for something that does the equivalent of:

set -o errexit

...in a Bash script. Ideally, the solution would raise an exception when the command fails (i.e., by checking for a non-zero return value), maybe with stderr as a message. This wouldn't be too hard to write, but it seems like this should exist already. Is there an option that I'm just not finding?

Answer 1

You can use one of ruby's special variables. The $? (analogous to the same shell script var).

`ls`
if $?.to_s == "0"
  # Ok to go
else
  # Not ok
end

Almost every program sets this var to 0 if everything went fine.

Answer 2

Easiest way would be to create a new function (or redefine an existing one) to call system() and check the error code.

Something like:

old_sys = system

def system(...)
  old_system(...)
  if $? != 0 then raise :some_exception
end

This should do what you want.