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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.

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2  
Into every directory, or selected ones? And the same script for each, or not? – enzotib Sep 24 '11 at 19:50
    
Every directory. The script in the directory named projectSettings.bash if it exists. – Prospero Sep 24 '11 at 19:54
    
Similar question on Stack Overflow – Gilles Feb 26 '15 at 23:41
up vote 36 down vote accepted

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
}
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1  
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! – Prospero Oct 2 '11 at 23:21
1  
I was completely wrong and apologize. RVM was overloading cd. – Prospero Oct 7 '11 at 14:22
2  
(removed some tangential pro/anti-Ruby stuff from this comment thread) – Michael Mrozek Jul 25 '12 at 21:04
1  
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. – spider Sep 18 '15 at 9:57
3  
@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! – Gilles Sep 18 '15 at 10:11

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