jpnevulator is a handy serial sniffer. You can use it to send data on a
serial device too. You can read or write from/to one or more serial
devices at the same time.

In write mode data to be sent on the serial device(s) is read from a
file or stdin in hexadecimal notation. Data is sent on the serial
device(s) line by line.

In read mode data to be read from the serial device(s) is written to a
file or stdout in hexadecimal notation. It's even possible to pass the
data in between the serial device(s). Several options enhance the
way the data is displayed.