Curl by default shows progress bar. To hide it -s option can be used. We can also add -S to show errors when -s option is used.
Curl with progress bar
$ curl https://dev.infoheap.com/ > /dev/null
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 37441 0 37441 0 0 32436 0 --:--:-- 0:00:01 --:--:-- 32444
Curl without progress bar (silent mode)
$ curl -sS https://dev.infoheap.com/ > /dev/null
This approach may be useful when fetching outcome of curl to a bash variable.