How to check your internal and external IP addresses from the command line
If your computer accesses the Internet via a local network connection, it will have an internal (LAN / WiFi) as well as an external (Internet) IP Address. If you need to reference either of these on a Unix machine, you can do so relatively easily from the command line.
Checking your internal IP address
To check the IP Address of your LAN / WiFi connection, ensure that Perl is installed, then run this command on the command line:
ifconfig | perl -nle '/inet [addr:]*(\S+)/ && print $1'
Explanation:
"ifconfig" will output your computer’s network interface parameters. These results will be piped into a Perl script with "perl -nle" running the specified line of code with line ending processing enabled and assuming a "while (<>) { … }" loop around the code. The "/inet [addr:]*(\S+)/ && print $1" line of code will output the IP Address section of the result of a regular expression search for lines containing "inet " followed by an optional "addr:".
Checking your external IP address
To check the address of your Internet connection, ensure that cURL is installed, then run this command on the command line:
curl -s http://checkip.dyndns.org | sed 's/[a-zA-Z/<> :]//g'
Explanation:
"curl -s http://checkip.dyndns.org" will fetch the source of the specified URL without displaying a progress meter or error messages. This result will be piped into sed, and "sed 's/[a-zA-Z/<> :]//g'" will replace all alphabetic characters, forward slashes, lesser than, greater than, space and colon characters with "" (nothing) globally (throughout the entire input, not just up to the first instance).
For more information on perl, curl and sed, use these commands:
man perl
man curl
man sed
perl --help
curl --help
sed --help
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