In our previous post How to connect to your 3D printer using picocom we showed how to open an interactive serial session on the command line using picocom. But you can also use picocom to run just a single command such as the M997 firmware update command:
echo "M997" | picocom -b 115200 /dev/ttyACM0 --imap lfcrlf --echo
If your USB serial device is named /dev/ttyUSB0 instead of /dev/ttyACM0 you can use this alternative version:
echo "M997" | picocom -b 115200 /dev/ttyUSB0 --imap lfcrlf --echo