Shell prompt that is based on location in filesystem

Question

I have to work within three main directories under the root filesystem - home/username, project, and scratch. I want my shell prompt to display which of these top level directories i am in.

Here is what I am trying to do:

top_level_dir ()
{
    if [[ "${PWD}" == *home* ]]
    then
        echo "home";
    elif [[ "${PWD}" == *scratch* ]]
    then
        echo "scratch";
    elif [[ "${PWD}" == *project* ]]
    then
        echo "project";
    fi

}

Then, I export PS1 as:

export PS1='$(top_level_dir) : '

Unfortunately this is not working as I want. I get home : for my prompt when I am in my home directory, but if I switch to scratch or projects then the prompt does not change. I do not understand bash scripting very well so I would appreciate any help to correct my code.

Answer 1

You can hook into cd to change the prompt every time you are changing the working directory. I've asked myself often how to hook into cd but I think that I now found a solution. What about adding this to your ~/.bashrc?:

#
# Wrapper function that is called if cd is invoked
# by the current shell
#
function cd {
    # call builtin cd. change to the new directory
    builtin cd $@
    # call a hook function that can use the new working directory
    # to decide what to do
    color_prompt
}

#
# Changes the color of the prompt depending
# on the current working directory
#
function color_prompt {
    pwd=$(pwd)
    if [[ "$pwd/" =~ ^/home/ ]] ; then
        PS1='\[\033[01;32m\]\u@\h:\w\[\033[00m\]\$ '
    elif [[ "$pwd/" =~ ^/etc/ ]] ; then
        PS1='\[\033[01;34m\]\u@\h:\w\[\033[00m\]\$ '
    elif [[ "$pwd/" =~ ^/tmp/ ]] ; then
        PS1='\[\033[01;33m\]\u@\h:\w\[\033[00m\]\$ '
    else
        PS1='\u@\h:\w\\$ '
    fi
    export PS1
}


# checking directory and setting prompt on shell startup
color_prompt