HTTP port code example

Example 1: lsof port

$ lsof -i :port
# ex. lsof -i :3000

Example 2: port range

Port numbers can run from 0 to 65353. Port numbers from 0 to 1023 are reserved 
for common TCP/IP applications and are called well-known ports. The use of 
well-known ports allows client applications to easily locate the corresponding 
server application processes on other hosts.