Question

Is it possible to listen on a port and run a command when a user attempts to connect to that port? Ideal application is for a server that should only be run when someone is actually using it. Windows or Linux solutions work.

Answer 1

linux/unix:

man nc

NAME
       nc - TCP/IP swiss army knife

some options that you may be interested

 -l           listen mode, for inbound connects
-p port      local port number (port numbers can be individual or ranges: lo-hi [inclusive])
 -e prog      specify program to exec after connect (use with caution)

i think nc is also available under windows platform.