What are the limits of whois command on unix?

Solution 1:

Your local linux box wont have a limit.

Web based ones will put a limit on to stop one user (/bot) from making zillions of requests and chewing up the service provider's data allowance/bandwidth/cpu/whatever other resources they are charged by.

Solution 2:

Command line whois, is a network client that talks to remote whois servers. Query limits on these servers exist, and are rather arbitrary and at the discretion of the registrar.

Here's an example using netcat (nc) to just send the domain name to the whois port on the whois server of the registrar DomainPeople.

$ echo foo.ca | nc whois.domainpeople.com 43
Domain name:           foo.ca
Domain status:         registered
Creation date:         2000/11/09
Expiry date:           2012/12/01
Updated date:          2010/10/22

% WHOIS look-up made at 2012-07-21 04:03:32 (GMT)
%
% Use of CIRA's WHOIS service is governed by the Terms of Use in its Legal
% Notice, available at http://www.cira.ca/legal-notice/?lang=en 
%
% (c) 2010 Canadian Internet Registration Authority, (http://www.cira.ca/)