from http://collectionofsolutions.blogspot.com/2008/05/making-sure-that-gzip-encoding-is.html

Making sure that GZIP encoding is turned on, using wget:

 wget --header="accept-encoding: gzip" "http://..."

If the saved response you get back is in binary gzip format instead of
text/html, then you know that your gzip encoding is turned on and functioning
correctly.