Execute bash scripts on entering a directory

Question

What is the best way to execute a script when entering into a directory?
When I move into a new directory I would like bash to execute the projectSettings.bash script much like RVM does.

Answer 1

You can make cd a function (and pop and pushd), and make it detect if you enter that particular directory.

cd () { builtin cd "$@" && chpwd; }
pushd () { builtin pushd "$@" && chpwd; }
popd () { builtin popd "$@" && chpwd; }
unset_all_project_settings () {
  # do whatever it takes to undo the effect of projectSettings.bash,
  # e.g. unset variables, remove PATH elements, etc.
}
chpwd () {
  case $PWD in
    /some/directory|/some/other/directory) . ./projectSettings.bash;;
    *) unset_all_project_settings;;
  esac
}

Do not do this in directories that you haven't whitelisted, because it would make it very easy for someone to trick you into running arbitrary code — send you an archive, so you unzip it, change into the directory it created, and you've now run the attacker's code.

I don't recommend this approach, because it means the script will be executed even if you enter that directory for some reason that's unrelated to working on the project. I suggest having a specific function that changes to the project directory and sources the settings script.

myproj () {
  cd /some/directory && . ./projectSettings.bash
}

Answer 2

direnv might be what you are looking for.

Here is an example taken from the official documentation:

$ 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