vlucas/phpdotenv — pull request #17 by pda (2014-02-04 02:53:40+00:00)
Title: Don't overwrite existing environment variables.

Ruby's dotenv does this with `ENV[key] ||= value`.

The point of dotenv / phpdotenv is to enable twelve-factor style configuration
via environment, so it's important to be able to override these `.env` files
with external environment variables.