whois
From Mac Guides
whois is a Terminal command to look up internet registry information on a particular domain. This is useful to see if a domain is already registered without visiting one of the registrar websites. whois requires an active internet connection.
[edit]
Examples
To look up information on macumors.com
whois macrumors.com
To see if a domain is available (look for 'No match for "SOMENOTREGISTEREDDOMAIN.COM".')
whois somenotregistereddomain.com
To see if a domain is available, filtering out all the lawyer babble. If it says "No match for...", the domain is available. If it says nothing, it's taken:
whois somenotregistereddomain.com | grep "No match for"
[edit]
Man Page Excerpt
The whois utility looks up records in the databases maintained by several Network Information Centers (NICs).
