Know process id by port number

Some time we want to know the process id using port number.Following is the command to use

Syntax:  $ lsof -i tcp:PORT_NUMBER

Example: lsof -i tcp:3000

Output:
COMMAND    PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
firefox-b        1837  ravi     46u   IPv4  87572      0t0    TCP localhost:51945->localhost:3000 (ESTABLISHED)
ruby             2846  ravi     8u     IPv4  49836      0t0    TCP *:3000 (LISTEN)
ruby             2846  ravi     9u     IPv4  78566      0t0    TCP localhost:3000->localhost:58605 (CLOSE_WAIT)

In output we can see 2846 is the ruby server id.