Question

I’m confused about how the $ variables work in this part of EventMachine code (strip_op is a String#sub method):

def receive_data(data)
      @buf = @buf ? @buf << data : data

      while (@buf && !@closing)
        case @parse_state
        when AWAITING_CONTROL_LINE
          case @buf
          when PUB_OP
            ctrace('PUB OP', strip_op($&)) if NATSD::Server.trace_flag?
            return connect_auth_timeout if @auth_pending
            @buf = $'
            @parse_state = AWAITING_MSG_PAYLOAD
            @msg_sub, @msg_reply, @msg_size = $1, $3, $4.to_i

What are the meanings for $&, $', $1, etc.?

Answer 1

Those hold parts of the last regex match. $&: the matched substring, $': the substring that follows the match, $1: the first captured substring of the match.