brname () {

  a=$(git rev-parse --abbrev-ref HEAD 2>/dev/null)
  if [ -n "$a" ]; then
    echo " [$a]"
  else
    echo ""
  fi

}

PS1="\u@\h:\w\$(brname)$ "

credit: daniel.haxx.se, https://news.ycombinator.com/item?id=25043731