Port forwarding using netcat

netcat (nc) is a really useful, if obscure command for managing and listening on TCP sockets.

I had a need to implement a local port forward on my machine. (more details coming).  I could use ssh to do this, but decided to write a simple shell script using nc instead.  Here’s the script, which I’m calling port_forward.sh

#!/bin/bash
# Run as root if your listening port is < 1024!

FIFO=$(mktemp -u)
trap "rm -f $FIFO; killall -9 nc; exit 255;" SIGINT SIGTERM SIGKILL
mkfifo $FIFO

while true; do
    # echo "Listening..."
    cat $FIFO | nc -k -l localhost $1 | nc localhost 6543 > $2
done

And then, you run it like this:

$ ./port_forward.sh 80 8080