Multipurpose relay (SOcket CAT).
# To listen to a port, wait for an incoming connection and transfer data to STDIO:
socat - TCP-LISTEN:8080,fork
# To listen on a port using SSL and print to STDOUT:
socat OPENSSL-LISTEN:4433,reuseaddr,cert=./cert.pem,cafile=./ca.cert.pem,key=./key.pem,verify=0 STDOUT
# To create a connection to a host and port, transfer data in STDIO to connected host:
socat - TCP4:www.example.com:80
# To forward incoming data of a local port to another host and port:
socat TCP-LISTEN:80,fork TCP4:www.example.com:80