Using direnv for project specific program versions

gistfile1.txt

We have 2 versions of program foo in /usr/bin/. We want to use foo-v1 in
project_a and foo-v2 in project_b.

$ foo-v1
This is version 1
I am located at /usr/bin/foo-v1

$ foo-v2
This is version 2
I am located at /usr/bin/foo-v2

First create project_a.  Create a project specific hidden directory in project
a and put a symlink to the foo version we want to use in this project.

$ mkdir project_a
$ cd project_a
$ mkdir -p .direnv/bin
$ ln -s /usr/bin/foo-v1 .direnv/bin/foo

Create a .envrc file. Specify the PATH_add function to prepend .direnv/bin to
the PATH when in project_a.

$ echo "PATH_add .direnv/bin" >>.envrc
$ direnv allow
direnv: loading ~/project_a/.envrc
direnv: export ~PATH

# Now, foo resolves to foo-v1 when you cd to project_a (or any subdir of project_a)
$ cd
$ cd project_a
direnv: loading ~/project_a/.envrc
direnv: export ~PATH

$ foo
This is version 1
I am located at /home/mmeffie/project_a/.direnv/bin/foo


Now create project_b, where foo will resolve to foo-v2.

$ mkdir project_b
$ cd project_b
$ mkdir -p .direnv/bin
$ ln -s /usr/bin/foo-v2 .direnv/bin/foo

$ echo "PATH_add .direnv/bin" >>.envrc
$ direnv allow
direnv: loading ~/project_a/.envrc
direnv: export ~PATH

$ foo
This is version 2
I am located at /usr/bin/foo-v2