Catches %s, but handles the stdin input via bash (i.e. <<<). Could probably have a stdin field in Job, and add it into the Popen in run_command, and follow it with a communicate(input=....), but it is so late at this point that I don't want to change the API on a whim.
Added some spacing.
Turns all %s into newlines in addition to making the first one '<<<' (stdin in bash shell).
Added code to extract the name and value for variable assignment, but I don't know how to set them up to run once I have them; all of that code is commented out. Replaces the %s more elegantly, and adjusted some error messages. Sidenote: croniter doesn't support '?'.