Das Buch Wer mitmacht, hat Recht!

When writing programs on Windows that involve I/O operations using the serial port, one quickly ends up loving Sysinternals Portmon.

I just found myself in a situation where I needed the exact same functionality, but on Linux.
What I found was jpnevulator.
It’s plain, simple, and if you’re on Debian or Ubuntu, just apt-get install jpnevulator and you’re good to go.

If you want to know what goes in and out over your serial port (in my case ttyUSB0), just use the tool like this:
hikari:~$ jpnevulator --read --ascii --tty /dev/ttyUSB0
76 3F 0D 56 20 20 20 31 31 31 20 20 34 30 30 2E v?.V 111 400.
30 30 20 20 37 32 30 2E 30 30 20 35 31 35 39 31 00 720.00 51591
0D .

On a side note:
You can use it to write data to a serial port, too.
Or monitor/write to several ports at the same time.
Quite a nice tool!

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Ubuntu package
Debian package
Official website