edit existing PS1; be more efficient

git-prompt.sh

# http://henrik.nyh.se/2008/12/git-dirty-prompt
# http://www.simplisticcomplexity.com/2008/03/13/show-your-git-branch-name-in-your-prompt/
#   username@Machine ~/dev/dir [master] $   # clean working directory
#   username@Machine ~/dev/dir [master*] $  # dirty working directory
# djmitche: *edit* an existing PS1 to add the git information
# djmitche: only invoke 'git' and 'sed' once (each) for each prompt
# djmitche: display [NO BRANCH] when not on a branch (e.g., during rebase -i)
# djmitche: almost completely replace with __git_ps1 from git contrib, which
#           gives more information and avoids calling git scripts if possible

# Based on:
#  http://repo.or.cz/w/git.git/blob/HEAD:/contrib/completion/git-completion.bash
# 
# Copyright (C) 2006,2007 Shawn O. Pearce <spearce@spearce.org>
# Conceptually based on gitcompletion (http://gitweb.hawaga.org.uk/).
# Distributed under the GNU General Public License, version 2.0.

# __gitdir accepts 0 or 1 arguments (i.e., location)
# returns location of .git repo
__gitdir ()
{
    if [ -z "${1-}" ]; then
        if [ -n "${__git_dir-}" ]; then
            echo "$__git_dir"
        elif [ -d .git ]; then
            echo .git
        else
            git rev-parse --git-dir 2>/dev/null
        fi
    elif [ -d "$1/.git" ]; then
        echo "$1/.git"
    else
        echo "$1"
    fi
}

# __git_ps1 accepts 0 or 1 arguments (i.e., format string)
# returns text to add to bash PS1 prompt (includes branch name)
__git_ps1 ()
{
    local g="$(__gitdir)"
    if [ -n "$g" ]; then
        local r
        local b
        if [ -f "$g/rebase-merge/interactive" ]; then
            r="|REBASE-i"
            b="$(cat "$g/rebase-merge/head-name")"
        elif [ -d "$g/rebase-merge" ]; then
            r="|REBASE-m"
            b="$(cat "$g/rebase-merge/head-name")"
        else
            if [ -d "$g/rebase-apply" ]; then
                if [ -f "$g/rebase-apply/rebasing" ]; then
                    r="|REBASE"
                elif [ -f "$g/rebase-apply/applying" ]; then
                    r="|AM"
                else
                    r="|AM/REBASE"
                fi
            elif [ -f "$g/MERGE_HEAD" ]; then
                r="|MERGING"
            elif [ -f "$g/BISECT_LOG" ]; then
                r="|BISECTING"
            fi

            b="$(git symbolic-ref HEAD 2>/dev/null)" || {

                b="$(
                case "${GIT_PS1_DESCRIBE_STYLE-}" in
                (contains)
                    git describe --contains HEAD ;;
                (branch)
                    git describe --contains --all HEAD ;;
                (describe)
                    git describe HEAD ;;
                (* | default)
                    git describe --exact-match HEAD ;;
                esac 2>/dev/null)" ||

                b="$(cut -c1-7 "$g/HEAD" 2>/dev/null)..." ||
                b="unknown"
                b="($b)"
            }
        fi

        local w
        local i
        local s
        local u
        local c

        if [ "true" = "$(git rev-parse --is-inside-git-dir 2>/dev/null)" ]; then
            if [ "true" = "$(git rev-parse --is-bare-repository 2>/dev/null)" ]; then
                c="BARE:"
            else
                b="GIT_DIR!"
            fi
        elif [ "true" = "$(git rev-parse --is-inside-work-tree 2>/dev/null)" ]; then
            if [ -n "${GIT_PS1_SHOWDIRTYSTATE-}" ]; then
                if [ "$(git config --bool bash.showDirtyState)" != "false" ]; then
                    git diff --no-ext-diff --quiet --exit-code || w="*"
                    if git rev-parse --quiet --verify HEAD >/dev/null; then
                        git diff-index --cached --quiet HEAD -- || i="+"
                    else
                        i="#"
                    fi
                fi
            fi
            if [ -n "${GIT_PS1_SHOWSTASHSTATE-}" ]; then
                    git rev-parse --verify refs/stash >/dev/null 2>&1 && s="$"
            fi

            if [ -n "${GIT_PS1_SHOWUNTRACKEDFILES-}" ]; then
               if [ -n "$(git ls-files --others --exclude-standard)" ]; then
                  u="%"
               fi
            fi
        fi

        local f="$w$i$s$u"
        printf "${1:- (%s)}" "$c${b##refs/heads/}${f:+ $f}$r"
    fi
}

# set up prefs
GIT_PS1_SHOWDIRTYSTATE=1

# append git info to the current prompt
export PS1=`echo "$PS1"|sed 's/\\\\w/\\\\w$(__git_ps1 " [%s]")/g'`