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isopen - a tool for reading port banners

About:

I wrote this as a replacement for telnet.

Originally, telnet was used to connect to hosts, but SSH has replaced that over time, because of encryption. Now, I use telnet mostly to connect to a port on a host to see if it's open and possibly what service is running on the port.
After connecting with telnet hitting ^] and typing 'exit' is a bummer. I wrote this so I won't have to anymore.

Use:

$ isopen 22
Trying 127.0.0.1:22...
Connected to 127.0.0.1:22
SSH-2.0-OpenSSH_7.6p1 Ubuntu-4

$ isopen 25
Trying 127.0.0.1:25...
Connected to 127.0.0.1:25
220 mako ESMTP Postfix (Ubuntu)

$ isopen keepbusy.fun 443
Trying 35.201.65.17:443... 
Port 443 is listening, but no data recieved.

Compile: make

Install: (as root)

make install
make replace_telnet

Undo: (as root)

make uninstall