Comment by croo

I write a bash script or two every month so I thought I'm okay. But then came along the very first example:

  trim_string() {
      # Usage: trim_string "   example   string    "
      : "${1#"${1%%[![:space:]]*}"}"
      : "${_%"${_##*[![:space:]]}"}"
      printf '%s\n' "$_"
  }

Ok, so the : is somehow a temporary variable... Then there is a variable starting at $ and you lost me :D Can someone break down that line for me? What the hell is going on here?

    : "${1#"${1%%[![:space:]]*}"}"