GZip Compression Check in curl

 1icasimpan@icasimpan.local:~$ curl -H "Accept-Encoding: gzip" -I -udemo:demo http://example.com
 2HTTP/1.1 200 OK
 3Date: Wed, 04 Oct 2017 15:25:48 GMT
 4Server: Apache/2.4.18 (Ubuntu)
 5X-Drupal-Cache: HIT
 6Etag: "1507130489-1"
 7Content-Language: en
 8X-Frame-Options: SAMEORIGIN
 9Link: </node/171>; rel="shortlink",</home>; rel="canonical"
10X-Generator: Drupal 7 (http://drupal.org)
11Cache-Control: public, max-age=60
12Last-Modified: Wed, 04 Oct 2017 15:21:29 GMT
13Expires: Sun, 19 Nov 1978 05:00:00 GMT
14Vary: Cookie,Accept-Encoding
15Content-Encoding: gzip
16Content-Type: text/html; charset=utf-8
...

Look at "Content-Encoding". It says 'gzip'.