Rudder

Tested behavior with:

import os
import unittest
from pprint import pprint

def env(option):
    if option.startswith("env:"):
        env_option = option.split(":", 1)[1]
        env_var = env_option.split("=", 1)
        if len(env_var) == 2:
            return env_var
            # os.environ[env_var[0]] = env_var[1]
        else:
            return None

class TestEnvOption(unittest.TestCase):

    def test_upper(self):
        self.assertEqual(env(""), None)
        self.assertEqual(env("--ignore"), None)
        self.assertEqual(env("env:"), None)
        self.assertEqual(env("env:NAME"), None)
        self.assertEqual(env("env:NAME=VALUE"), ["NAME", "VALUE"])
        # allow unsetting a variable
        self.assertEqual(env("env:NAME="), ["NAME", ""])
        self.assertEqual(env("env:NAME=VALUE=PLOP"), ["NAME", "VALUE=PLOP"])

if __name__ == "__main__":
    unittest.main()

Applied in changeset ncf|6e08b5544498a1e64303b8651fa594056105928d.