It’s sometimes useful to know your computer’s external IP address: that is, the IP address of your NAT router as seen from the outside world. It would be most convenient to be able to do this from a shell, without having to resort to a web site like this one. A quick DuckDuckGo search found this older discussion, but nearly all of the methods described there no longer work. The only ones that worked for me were this:
curl -s http://whatismyip.akamai.com/ && echo
dig +short -t txt o-o.myaddr.l.google.com @ns1.google.com | sed -e s/\"//g
Either or these commands could be placed in a one-line shell script or an alias.