Useful Linux Commands

Networking tools

netcat

nc [options] host port

The most basic command to find if a port is open would be $ nc -z -v 192.168.1.71 80 which would return:

192.168.1.71: inverse host lookup failed: Unknown host
(UNKNOWN) [192.168.1.71] 80 (http) open

The result on the last line shows open, which means port 80 is open. The error before that just means that netcat tried to do a reverse lookup on the IP address but couldn’t find this. So this error can be safely ignored. The -z option tells nc to only scan for open ports without sending an data to them while the -v option means provide more verbose information.

echo "GET" | nc 192.168.1.71 80 to check if you can connect to a http server at 192.168.1.71 in the event you do not have wget or curl.

wget

A tool to check web connections.

$ wget --spider http://192.168.1.70

iperf3

This is a tool to check network bandwidth performance

Regex symbols

Given below are a list of notations used for regex matching:

. Any one character
* Match any number of previous (including 0)
+ Match any number of previous
$ End of line
^ Beginning of line
S any non-white character
s any whitespace character
? optional
[a-z] any lowercase letter
[A-Z] any uppercase letter
[A-Za-z] any letter
\ escape something