I found command line - How to connect to a serial port as simple as using SSH? - Unix & Linux Stack Exchange.
Hacked it a bit and it does reset a Leonardo (Ubuntu 12.04; yes I need an update)
#!/bin/sh
# connect.sh
# Usage:
# $ connect.sh <device> <port speed>
# Example: connect.sh /dev/ttyS0 9600
# Set up device
stty -F $1 $2
dmesg | tail -f
# Let cat read the device $1 in the background
cat $1 &
# Capture PID of background process so it is possible to terminate it when done
bgPid=$!
# Terminate background read process
kill $bgPid
dmesg | tail -f
I added dmesg to see, but not sure if it's useful.
Run with port and baudrate as parameters.