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.

Solution 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
}

Solution 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

Solution 3

It's my cd function

function cd()
{
    if [ -f .exit.sh ]; then
        source .exit.sh;
    fi

    if [ -z $* ]; then
        builtin cd ~
    else
        builtin cd "$*"
    fi

    if [ -f .enter.sh ]; then
        source .enter.sh;
    fi
}

And then you can write your script in ".enter.sh" or ".exit.sh".

Comments

[Admin]

Into every directory, or selected ones? And the same script for each, or not?

[Admin]

Every directory. The script in the directory named projectSettings.bash if it exists.

[James Andino]

I only started in Ruby a little while ago. The RVM tool tho is completely in Bash and one of the best pieces of Bash magic I have seen. I think the answer is a little silly because one of the absolutely worse things you can ever do is over ride something like cd and there is with out doubt a better way. Even using $PROMPT_COMMAND is better!

[Gilles 'SO- stop being evil']

@JamesAndino In zsh I'd use chpwd. Lacking an exact equivalent in bash, overloading cd feels reasonable. With PROMPT_COMMAND, your per-directory settings will be set later if you run cd foo; somecommand and not at all if you run (cd foo; somecommand) (this may or may not be what you want).

[James Andino]

They do it here using just BASH with out overloading PROMPT_COMMAND or cd github.com/wayneeseguin/rvm I tried to unlock the secret but failed.

[James Andino]

I was completely wrong and apologize. RVM was overloading cd.

[Michael Mrozek]

(removed some tangential pro/anti-Ruby stuff from this comment thread)

[New Alexandria]

In our work environment we already use aliases to nav to the common repos, thus the last part of this answer is the most useful for us. Thanks!

[J A]

in the projectSettings.bash I suggest you to add a flag variable to not repeat the initialization in case you exit/re-enter the directory. So enclose everything in if [ -z $MYSETTINGS ] ; then export MYSETTINGS=1 ; echo your settings here ; fi. This is to avoid problems in case you do something PATH=/mytools/bin:$PATH kind of initialisation.

[Gilles 'SO- stop being evil']

@spider Rather there should be some kind of unset mechanism if you leave the directory. If you leave and reenter, you should get the settings back!

[J A]

@Gilles Yeah, you're right.