bash script for git branch recognition

.profile

function find_git_branch {
    local dir=. head
    until [ "$dir" -ef / ]; do
        if [ -f "$dir/.git/HEAD" ]; then
            head=$(< "$dir/.git/HEAD")
            if [[ $head == ref:\ refs/heads/* ]]; then
                git_branch=" (${head#*/*/})"
            elif [[ $head != '' ]]; then
                git_branch=' (detached)'
            else
                git_branch=' (unknown)'
            fi  
            return
        fi  
        dir="../$dir"
    done
    git_branch=''
}

green=$'\e[1;32m'
magenta=$'\e[1;35m'
normal_colours=$'\e[m'
PROMPT_COMMAND="find_git_branch; $PROMPT_COMMAND"
PS1="\[$green\]\u@\h:\W\[$magenta\]\$git_branch\[$green\]\\$\[$normal_colours\] "