Bash script to check if a public HTTPS site is up

One of many:

if curl -s --head  --request GET https://example.com | grep "200 OK" > /dev/null; then 
   echo "mysite.com is UP"
else
   echo "mysite.com is DOWN"
fi

Here is a way to do it using wget instead of curl. Keep in mind that MacOS doesn't come with wget by default.

A successful web request will return a code of 200, a failure will return a 300, 400, 404, ect... (see REST API codes)

This line will return a 1 if the web request was successful, otherwise it will return 0

wget -q  -O /tmp/foo google.com | grep '200' /tmp/foo | wc -l
1

Nagios' check_http plugin can do this and much more, including checking for specific text in the response. You can run it from a shell script independently of Nagios itself:

$ check_http --ssl -H www.google.com -r 'Feeling Lucky'
HTTP OK: HTTP/1.1 200 OK - 11900 bytes in 0.086 second response time |time=0.085943s;;;0.000000 size=11900B;;;0

$ echo $?
0