while true; do
	date -Iseconds >> onlinenet2.log;
	curl -s -S -n http://ipv4.download.thinkbroadband.com/100MB.zip -o /dev/null -w '%{time_total},%{size_download},%{speed_download}\n' >> onlinenet2.log;
done

out

2020-02-18T23:43:33+08:00
28.245440,104857600,3712430.000
2020-02-18T23:44:02+08:00
21.179271,104857600,4951017.000
2020-02-18T23:44:23+08:00
47.273182,104857600,2218128.000
2020-02-18T23:45:10+08:00
82.253273,104857600,1274817.000
2020-02-18T23:46:33+08:00
41.593911,104857600,2521039.000
2020-02-18T23:47:14+08:00
72.786970,104857600,1440628.000
2020-02-18T23:48:27+08:00
67.240456,104857600,1559452.000
2020-02-18T23:49:35+08:00
123.313491,104857600,850336.000
2020-02-18T23:51:38+08:00
228.086542,104857600,459728.000
2020-02-18T23:55:26+08:00
107.651076,104857600,974051.000
2020-02-18T23:57:14+08:00
128.396680,104857600,816673.000
2020-02-18T23:59:23+08:00