Most efficient way to programmatically determine if a web domain is available?

Question

I am writing some code to determine whether a network domain is registered. For example, I want to check if "Google123.com" is available. There are at least two ways I can do this programmatically, but I'm not sure which is more valid:

• A) In linux/cygwin, I can launch the whois command to see if a domain is in use.
• B) In linux/windows, i can launch nslookup command to see if a domain is resolvable.

My questions are:

1. Is nslookup really a valid way to check for registration? Does every registered domain have a name server and show up in DNS?
2. What is the fastest way to make this registration check? Any tips or other ways to do it?

Answer 1

In regards to #1, no. There is no requirement that registered domains actually have DNS.

Answer 2

There are rumours that some of the web sites out there that allow you to search for domains are actually fronts for domain speculators who will buy up the domain as soon as you search for it, and then try to sell it for you. I've never encountered such a scam, but you might want to try a few garbage domain searches on a new site before searching for your dream domain name.