direnv is an environment switcher for the shell. It knows how to hook into bash, zsh, tcsh and fish shell to load or unload environment variables depending on the current directory. This allows to have project-specific environment variables and not clutter the "~/.profile" file.

Before each prompt it checks for the existence of an ".envrc" file in the current and parent directories. If the file exists (and authorized), it is loaded into a bash sub-shell and all exported variables are then captured by direnv and then made available the current shell.

Because direnv is compiled into a single static executable it is fast enough to be unnoticeable on each prompt. It is also language agnostic and can be used to build solutions similar to rbenv, pyenv, phpenv, ...

$ cd ~/my_project
$ echo ${FOO-nope}
nope
$ echo export FOO=foo > .envrc
.envrc is not allowed
$ direnv allow .
direnv: reloading
direnv: loading .envrc
direnv export: +FOO
$ echo ${FOO-nope}
foo
$ cd ..
direnv: unloading
direnv export: ~PATH
$ echo ${FOO-nope}
nope

Dependencies: make, golang

git clone https://github.com/direnv/direnv
cd direnv
make install
# or symlink ./direnv into the $PATH

There's package definitions on Homebrew, Arch's AUR, Gentoo go-overlay overlay and NixOS's nixpkgs.

Links to binary builds are also available on each release.

For direnv to work properly it needs to be hooked into the shell. Each shell has its own extension mechanism:

Add the following line at the end of the "~/.bashrc" file:

eval "$(direnv hook bash)"

Make sure it appears even after rvm, git-prompt and other shell extensions that manipulate the prompt.

Add the following line at the end of the "~/.zshrc" file:

eval "$(direnv hook zsh)"

Add the following line at the end of the "~/.config/fish/config.fish" file:

eval (direnv hook fish)

Add the following line at the end of the "~/.cshrc" file:

eval `direnv hook tcsh`

In some target folder, create an ".envrc" file and add some export(1) directives in it.

Note that the contents of the .envrc file must be valid bash syntax, despite what shell you may be using. This is because direnv always executes the .envrc with bash (a sort of lowest common denominator of UNIX shells) so that direnv can work across shells. If you try to use some syntax that doesn't work in bash (like zsh's nested expansions), you will run into trouble.

On the next prompt you will notice that direnv complains about the ".envrc" being blocked. This is the security mechanism to avoid loading new files automatically. Otherwise any git repo that you pull, or tar archive that you unpack, would be able to wipe your hard drive once you cd into it.

So here we are pretty sure that it won't do anything bad. Type direnv allow . and watch direnv loading your new environment. Note that direnv edit . is a handy shortcut that opens the file in your $EDITOR and automatically allows it if the file's modification time has changed.

Now that the environment is loaded you can notice that once you cd out of the directory it automatically gets unloaded. If you cd back into it it's loaded again. That's the base of the mechanism that allows you to build cool things.

Exporting variables by hand is a bit repetitive so direnv provides a set of utility functions that are made available in the context of the ".envrc" file.

As an example, the PATH_add function is used to expand and prepend a path to the $PATH environment variable. Instead of export $PATH=$PWD/bin:$PATH you can write PATH_add bin. It's shorter and avoid a common mistake where $PATH=bin.

To find the documentation for all available functions check the direnv-stdlib(1) man page.

It's also possible to create your own extensions by creating a bash file at "/.config/direnv/direnvrc" or "/.direnvrc". This file is loaded before your ".envrc" and thus allows you to make your own extensions to direnv.

Lets say you have the following structure:

• "/a/.envrc"
• "/a/b/.envrc"

If you add the following line in "/a/b/.envrc", you can load both of the ".envrc" when you are in /a/b:

source_env ..

• Environment Modules - one of the oldest (in a good way) environment loading system
• autoenv - lightweight, doesn't support unloads
• zsh-autoenv - a feature-rich mixture of autoenv and smartcd: enter/leave events, nesting, stashing (Zsh-only).

Bug reports, contributions and forks are welcome.

All bugs or other forms of discussion happen on http://github.com/direnv/direnv/issues

There is also a wiki available where you can share your usage patterns or other tips and tricks https://github.com/direnv/direnv/wiki

Or drop by on IRC (#direnv on freenode) to have a chat.

Copyright (C) 2014 shared by all contributors under the MIT licence.