What once started as a Jackpot Navigator emulator (hence the strange name) is now a nice serial sniffer and you can use it to send data on a serial line too. It’s sort of like a very simple terminal emulator, like picocom. But jpnevulator uses hexadecimal byte values to display and send along the line. Very handy indeed if you are working a lot with serial protocols.

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. Several options enhance the way the data is displayed.

[ http://jpnevulator.snarl.nl/ ]

To sniff your printer you would use command like this: jpevulator –ascii –tty /dev/usb/lp) –read