How to get the full redirect url in curl ?

curl’s -w option and the sub variable url_effective is what you are looking for.

Something like

curl -Ls -o /dev/null -w %{url_effective} http://google.com

More info

-L         Follow redirects
-s         Silent mode. Don't output anything
-o FILE    Write output to <file> instead of stdout
-w FORMAT  What to output after completion