bash function to provide improved Git status indicator in primary prompt

gistfile1.sh

parse_git_branch () {

    local stat
    if ! stat=`git status -sb 2>/dev/null` || [[ -n $NO_GIT_PROMPT ]]; then
        return
    fi

    local ref=`sed -nr '/^##/{s/^## (Initial commit on )?//;p}' <<<"$stat"`

    local dirty=`
        awk '
            NR >= 2 {
                if ($1 ~ /^\?\?/)
                    untrk="?"
                else if ($1 ~ /^(AA|DD)/ || $1 ~ /^.?U/)
                    cf = "!"
                else {
                    fs = substr($0, 0, 2)
                    if (fs ~ /^.[^ ]/)
                        wd = "*"
                    if (fs ~ /^[^ ]/)
                        idx = "^"
                }
            }
            END { print wd idx untrk cf }
        ' <<<"$stat"
    `

    local stashed
    [[ -n `git stash list 2>/dev/null` ]] &&
        stashed=$

    local g
    [[ -d .git ]] &&
        g=.git ||
        g=`git rev-parse --git-dir 2>/dev/null`
    local svnrefspec svn ahead behind
    if svnrefspec=`git config --get svn-remote.svn.fetch`; then
        svn=-svn
        local revlist=`git rev-list --left-right HEAD...${svnrefspec##*:}`
        ahead=`grep -c '^<' <<<"$revlist"`
        [[ $ahead -eq 0 ]] &&
            ahead=
        behind=`grep -c '^>' <<<"$revlist"`
        [[ $behind -eq 0 ]] &&
            behind=
    else
        ahead=`sed -nr 's/.*\[ahead ([[:digit:]]+).*\]/\1/;Tq;p;:q' <<<"$ref"`
        behind=`
            sed -nr '
                s/.*\[(ahead [[:digit:]]+, )?behind ([[:digit:]]+).*\]/\2/
                Tq
                p
                :q
            ' <<<"$ref"
        `
    fi
    [[ -n $ahead ]] &&
        ahead=+$ahead
    [[ -n $behind ]] &&
        behind=-$behind

    local flag
    if [[ -d "$g/rebase-merge" || -f "$g/rebase-apply/rebasing" ]]; then
        flag=R
    elif [[ -d "$g/rebase-apply" ]]; then
        flag=A
    elif [[ -f "$g/MERGE_HEAD" ]]; then
        flag=M
    elif [[ -f "$g/CHERRY_PICK_HEAD" ]]; then
        flag=C
    elif [[ -f "$g/BISECT_LOG" ]]; then
        flag=B
    fi
    [[ -n $flag ]] &&
        flag=:$flag

    [[ $ref == *\(no\ branch\)* ]] &&
        ref=\<`git rev-parse --short HEAD`:`
            git name-rev HEAD |
            sed 's/[^ ]* //'
        `\> ||
        ref=${ref%%[ .]*}

    echo -n " (git$svn:$ref$ahead$behind$dirty$stashed$flag)"

}