Using curl to check on site availability

The easy way to check if a site is available, is by using curl. For example, if you want to check whether www.google.com is available or not, jut run:

$ curl -I www.google.com

HTTP/1.1 200 OK

Date: Thu, 25 Apr 2013 06:03:06 GMT

Expires: -1

Cache-Control: private, max-age=0

Content-Type: text/html; charset=ISO-8859-1

Set-Cookie: PREF=ID=f4eacf44ddfe9913:FF=0:TM=1366869786:LM=1366869786:S=pD4jQT9xbgTOjuKG; expires=Sat, 25-Apr-2015 06:03:06 GMT; path=/; domain=.google.com

Set-Cookie: NID=67=KULBN37y3Mw7TIYNurxqV3L9OAm0gaj4VhRxz0_OsayoTS8C7nPN9QLCMovAzkVxhKfoop1EcHjWiBWjv7Vxl2C5iQ-Z8J0zcVtv4YfrJXs2ypRegbp2Y8MPcJjTyX1p; expires=Fri, 25-Oct-2013 06:03:06 GMT; path=/; domain=.google.com; HttpOnly

P3P: CP="This is not a P3P policy! See http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=151657 for more info."

Server: gws

X-XSS-Protection: 1; mode=block

X-Frame-Options: SAMEORIGIN

Transfer-Encoding: chunked 

with -I for fetching the HTTP-header only. In this case the return code is 200, and it means the site is available.