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

Definitely quite fast. only problem is it stills says "master", even if I go outside a git repo, eg into /tmp

http://lists.gnu.org/archive/html/bug-bash/2014-03/msg00036.html discusses a fix for an old bash bug regarding tilde ~ expansion introduced between bash 4.2 and bash 4.3 which changes the behavior of this code on line 68 and line 71.

To share my .bashrc between two machines running different versions of bash I had to add a variable just to use for tilde replacement. Otherwise escape chars or quoting work on one version, but print or expand improperly on another.

    case $TERM in
        xterm*|rxvt*|Eterm)
        local tilde="~"
        if [ $USER == "root" ];
        then
            echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/$HOME/$tilde}\007"
        else

            echo -ne "\033]0;${HOSTNAME%%.*}:${PWD/$HOME/$tilde}\007"
        fi
        ;;
    screen)
        echo -ne "\033_${USER}@${HOSTNAME%%.*}:${PWD/$HOME/$tilde}\033\\"
        ;;
    esac

Also to work correctly under tmux default PS1 for root (line 10) should be
export PS1="\[\e[1;31m\]\u\[\e[0m\] \[\e[1;33m\]\w\[\e[0m\] ";
note \[ in the beginning

Thanks for posting this; very useful.

L52 .. What does that do?
Just trying to understand your script.

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)!