My very fast Bash prompt, which shows git branch, virtualenv, and background jobs

profile

# prompt examples:
#   [3 jobs master virtualenv] ~/code/myproject/foo
#   [1 job my-branch virtualenv] ~/code/bar/
#   [virtualenv] ~/code/
#   ~
# Very, very fast, only requiring a couple of fork()s (and no forking at all to determine the current git branch)

if [[ "$USER" == "root" ]]
then
    export PS1="\e[1;31m\]\u \[\e[1;33m\]\w\[\e[0m\] ";
else
    export PS1="\[\e[1;33m\]\w\[\e[0m\] ";
fi

# 100% pure Bash (no forking) function to determine the name of the current git branch
gitbranch() {
    export GITBRANCH=""

    local repo="${_GITBRANCH_LAST_REPO-}"
    local gitdir=""
    [[ ! -z "$repo" ]] && gitdir="$repo/.git"

    # If we don't have a last seen git repo, or we are in a different directory
    if [[ -z "$repo" || "$PWD" != "$repo"* || ! -e "$gitdir" ]]; then
        local cur="$PWD"
        while [[ ! -z "$cur" ]]; do
            if [[ -e "$cur/.git" ]]; then
                repo="$cur"
                gitdir="$cur/.git"
                break
            fi
            cur="${cur%/*}"
        done
    fi

    if [[ -z "$gitdir" ]]; then
        unset _GITBRANCH_LAST_REPO
        return 0
    fi
    export _GITBRANCH_LAST_REPO="${repo}"
    local head=""
    local branch=""
    read head < "$gitdir/HEAD"
    case "$head" in
        ref:*)
            branch="${head##*/}"
            ;;
        "")
            branch=""
            ;;
        *)
            branch="d:${head:0:7}"
            ;;
    esac
    if [[ -z "$branch" ]]; then
        return 0
    fi
    export GITBRANCH="$branch"
}

PS1_green='\[\e[32m\]'
PS1_blue='\[\e[34m\]'
PS1_reset='\[\e[0m\]'
_mk_prompt() {
    # Change the window title of X terminals 
    case $TERM in
        xterm*|rxvt*|Eterm)
            echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/$HOME/~}\007"
           ;;
        screen)
            echo -ne "\033_${USER}@${HOSTNAME%%.*}:${PWD/$HOME/~}\033\\"
          ;;
    esac

    # Un-screw virtualenv stuff
    if [[ ! -z "${_OLD_VIRTUAL_PS1-}" ]]; then
        export PS1="$_OLD_VIRTUAL_PS1"
        unset _OLD_VIRTUAL_PS1
    fi

    if [[ -z "${_MK_PROMPT_ORIG_PS1-}" ]]; then
        export _MK_PROMPT_ORIG_PS1="$PS1"
    fi

    local prefix=()
    local jobcount="$(jobs -p | wc -l)"
    if [[ "$jobcount" -gt 0 ]]; then
        local job="${jobcount##* } job"
        [[ "$jobcount" -gt 1 ]] && job="${job}s"
        prefix+=("$job")
    fi

    gitbranch
    if [[ ! -z "$GITBRANCH" ]]; then
        prefix+=("${PS1_green}$GITBRANCH${PS1_reset}")
    fi

    local virtualenv="${VIRTUAL_ENV##*/}"
    if [[ ! -z "$virtualenv" ]]; then
        prefix+=("${PS1_blue}$virtualenv${PS1_reset}")
    fi

    PS1="$_MK_PROMPT_ORIG_PS1"
    if [[ ! -z "$prefix" ]]; then
        PS1="[${prefix[@]}] $PS1"
    fi

    export PS1
}
export PROMPT_COMMAND=_mk_prompt

Thank you for this gist. It really made a difference on windows using msys2 (~80ms down to ~3ms)
I modified it to be simpler and it can be found here https://gist.github.com/Ragnoroct/c4c3bf37913afb9469d8fc8cffea5b2f

@Ragnoroct's gist ☝️ is indeed super fast; it also omits the branch if you're not in a git repository. I modified that even further to optimize speed slightly more with PROMPT_COMMAND. Thanks so much for the effort on this by the folks above (for me it would have been impractical, if not impossible, otherwise)!