edit existing PS1; be more efficient

.bashrc

# 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

function __git_info {
  local status dirty branch
  status=$(git status 2> /dev/null)
  test -z "$status" && return
  [[ "$status" =~ "working directory clean" ]] || dirty="*"
  branch=$(sed '1{s/.*branch \(.*\).*/\1/g;q}' <<<"$status")
  echo " [$branch$dirty]"
}

# append git info to the current prompt
export PS1=`echo "$PS1"|sed 's/\\\\w/\\\\w$(__git_info)/g'`
#export PS1='\u@\h \[\033[1;33m\]\w\[\033[0m\]$(__git_info)$ '