Autoenv: Directory-based Environments 
Magic per-project shell environments. Very pretentious.
Note: you should probably use direnv instead.
Simply put, it is higher quality software. But, autoenv is still great,
too. Maybe try both? :)
This image sums up the relationship between the two projects, very well:

What is it?
If a directory contains a .env file, it will automatically be executed
when you cd into it. When enabled (set AUTOENV_ENABLE_LEAVE to a
non-null string), if a directory contains a .env.leave file, it will
automatically be executed when you leave it.
This is great for...
- auto-activating virtualenvs
- auto-deactivating virtualenvs
- project-specific environment variables
- making millions
You can also nest envs within each other. How awesome is that!?
When executing, autoenv, will walk up the directories until the mount
point and execute all .env files beginning at the top.
Usage
Follow the white rabbit:
$ echo "echo 'whoa'" > project/.env
$ cd project
whoa

Install
Install it easily:
Mac OS X Using Homebrew
$ brew install autoenv
$ echo "source $(brew --prefix autoenv)/activate.sh" >> ~/.bash_profile
Using pip
$ pip install autoenv
$ echo "source `which activate.sh`" >> ~/.bashrc
Using git
$ git clone git://github.com/inishchith/autoenv.git ~/.autoenv
$ echo 'source ~/.autoenv/activate.sh' >> ~/.bashrc
Using AUR
Arch Linux users can install
autoenv or
autoenv-git with
their favorite AUR helper.
You need to source activate.sh in your bashrc afterwards:
$ echo 'source /usr/share/autoenv/activate.sh' >> ~/.bashrc
Configuration
Before sourcing activate.sh, you can set the following variables:
AUTOENV_AUTH_FILE: Authorized env files, defaults to
~/.autoenv_authorizedAUTOENV_ENV_FILENAME: Name of the.envfile, defaults to.envAUTOENV_LOWER_FIRST: Set this variable to flip the order of.env
files executedAUTOENV_ENV_LEAVE_FILENAME: Name of the.env.leavefile,
defaults to.env.leaveAUTOENV_ENABLE_LEAVE: Set this to a non-null string in order to
enable source env when leavingAUTOENV_ASSUME_YES: Set this variable to silently authorize the
initialization of new environments
Shells
autoenv is tested on:
- bash
- zsh
- dash
- fish is supported by
autoenv_fish - more to come
Alternatives
Direnv is an excellent alternative to autoenv, and includes the ability
to unset environment variables as well. It also supports the fish
terminal.
Disclaimer
Autoenv overrides cd. If you already do this, invoke autoenv_init
within your custom cd after sourcing activate.sh.
Autoenv can be disabled via unset cd if you experience I/O issues with
certain file systems, particularly those that are FUSE-based (such as
smbnetfs).
Attributions
autoenv is one of @kennethreitz:org project and is now owned and maintained by @inishchith.