For me, it has nothing to do with the number of lines, but the amount of actual computation I am doing. If all I need to do is wire up the inputs and outputs of X commands, then shell script is the best tool for the job.

If I actually need to do something with an input or output before sending it to the next command, I'll switch to Python.

For CLI tasks in Python, http://docopt.org/ and http://shell-command.readthedocs.org/en/latest/ are invaluable tools. Yes, I know about Envoy, but shell_command is much nicer to use in my opinion. Envoy doesn't automatically escape arguments, which is annoying for all the reasons that SQL injections are annoying.