lsof -i :8080 | awk 'NR > 1 {print $2}' | xargs --no-run-if-empty kill
lsof lists open files (ls-o-f, get it?). lsof -i :8080 lists open files on address ending in :8080. The output looks like this
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
chrome 2619 qymspace 149u IPv4 71595 0t0 TCP localhost:53878->localhost:http-alt (CLOSE_WAIT)`
We use awk 'NR > 1 {print $2}' to print the second column for lines except the first. The result is a list of PIDs, which we pipe to xargs kill to kill.
The --no-run-if-empty option of xargs is available in GNU implementations, and typically not available in BSD implementations. Without this option, the one-liner will raise an error if there are no matches (no PIDs to kill).
lsof -i :8080 | awk '{print $2}' | tail -n 1 | xargs kill