Bash alias to run a command in npm or yarn

npm-or-yarn.bash

# Pass arguments to whichever of npm or yarn is managing the current directory's
# workspace.
alias yn=npm/yarn
function npm/yarn() {
  local package_manager # this will be initialized to yarn or npm
  local dir=$(pwd)

  while true; do
    if [[ -f "$dir/package.json" ]]; then
      if [[ -f "$dir/package-lock.json" ]]; then
        package_manager="npm"
        break
      fi
      if [[ -f "$dir/yarn.lock" ]]; then
        package_manager="yarn"
        break
      fi
      package_manager="npm"
    fi

    current_dir=$dir
    dir=$(dirname "$dir")
    if [[ "$dir" == "/" || "$dir" == "$current_dir" ]]; then
      if [[ -z "$package_manager" ]]; then
        echo "Error: package.json not found in current working directory or a directory that contains it" 1>&2
        return 1
      else
        echo "Warning: package-lock.json or yarn.lock not found; assuming $package_manager" 1>&2
      fi
    fi
  done

  $package_manager $@
}