automatically add current node-binary path to $PATH

.bashrc

LAST_PWD=""
LAST_NPM_BIN=""
# find the npm binary path for a given directory ($1). 
# Mostly equivalent to calling `npm bin` (except it doesn't report 
# non-existing directories), but around 40x faster.
function fastNpmBin() {
  local dir="${1}"
  local candidate=""
  
  while [ "${dir}" != "/" ] ; do 
    candidate="${dir}/node_modules/.bin"
    if [ -d "${candidate}" ] ; then 
      echo -n "${candidate}" 
      return 0
    fi
    dir=`dirname "${dir}"`
  done
  
  return 1
}

function updatePath() {
  # dont do anything if we did stay in the same directory 
  if [ "$(pwd)" == "${LAST_PWD}" ] ; then return; fi
  
  # store pwd to prevent rechecking
  LAST_PWD="$(pwd)"

  # get npm bin
  local npmBin="$(fastNpmBin ${LAST_PWD})"
  
  # check if npmBin changed since the last path-update
  if [ "${npmBin}" != "${LAST_NPM_BIN}" ] ; then
    # purge all entries for commands from node_modules/.bin from the 
    # path-lookup cache
    hash -l | grep node_modules/.bin | while read x x x x name ; do
      hash -d "${name}"
    done

    LAST_NPM_BIN="${npmBin}"

    # remove any previous PATH-entries containing `node_modules/.bin` and 
    # prepend the new bin-dir
    PATH="${npmBin}$(
      IFS=':'
      for d in $PATH ; do
        [[ "${d/node_modules\/.bin/}" != "${d}" ]] || printf ":$d"
      done
    )"
    
    # remove a trailing colon (if $npmBin is empty)
    export PATH=${PATH#:}
  fi
}
export PROMPT_COMMAND=updatePath