Override `cd` or other builtin functions more than once

Question

Say I have this bash function:

cd(){
 builtin cd "$@"
 echo "do my own thing"
}

the problem is that if I override cd in another place, only 1 override will count, any other override will be overwritten by the latest sourced function!

Is there a way to have multiple cd functions and for them to all be called?

I am thinking something like this:

alias prev_cd="cd";

cd(){
   prev_cd  
   echo "do my own thing"
}

but I doubt that's quite right..the problem with the prev_cd solution is that it will result in an infinite loop. Where prev_cd calls my cd function, and vice versa. I only want prev_cd to be defined as cd definitions outside of this file..

One trick I can use is I can find the file that the cd function is located in using:

shopt -s extdebug
declare -F cd
shopt -u extdebug

if I have already overridden the cd command, I can call unset -f cd?

It looks like RVM (Ruby Version Manager) overrides cd:

cd 14 /Users/alexamil/.rvm/scripts/cd

so I don't want to mess up previous overrides of cd..so I only want to override cd if I don't mess up the previous overrides...

Answer 1

You can copy the body of the cd definition into a new function with the prev_cd name. Use declare -f cd to get that definition and then eval to redefine that.

definition_prev_cd="prev_$(declare -f cd)"
eval "${definition_prev_cd}"
unset definition_prev_cd  # clean up, no reason to leave this string around

cd () {
   prev_cd "$@"
   echo "do my own thing"
}

You could add some checks or create a generic function to copy arbitrary functions, but this should be enough to get you to solve the problem you described...