how to detect and interpret serial port data. I have "googled" a lot but I don't find a "general explanation". I have a couple of protocol specifications for serial devices, which I want to talk with and read from. The biggest hurdle for me is to get the "data stream" out of a continuous message

I've never seen such a tutorial, and I've been playing with serial ports for 30+ years. Mind you, I haven't gone looking for a long time either :)

There are basically two types of serial line protocol:

• Length-prefixed based.

  With this, the first 1, 2, or 4 characters from the stream identify how many more characters must be read for a complete, single message:

  <0x1A>This is a complete message
  [download]

• Terminator based.

  With this, you have to keep reading until you see the specified terminator:

  This is a complete message<0x03>
  [download]

In general, the former is easier and more efficient to deal with at the lower level.

However, at the higher level, the latter allows you to use filetype line-oriented reads and writes provided that your libraries allow you to set the EOL character -- which Perl allows by the setting of $/ & $\.