Efficiently test if a port is open on Linux?

Question

From a bash script how can I quickly find out whether a port 445 is open/listening on a server.

I have tried a couple of options, but I want something q

Answer 1

There's a very short with "fast answer" here : How to test if remote TCP port is opened from Shell script?

nc -z  ; echo $?

I use it with 127.0.0.1 as "remote" address.

this returns "0" if the port is open and "1" if the port is closed

e.g.

nc -z 127.0.0.1 80; echo $?

-z Specifies that nc should just scan for listening daemons, without sending any data to them. It is an error to use this option in conjunc- tion with the -l option.