Apache 2.4 – HTTP Header Regex Match Guide

I think the following Perl regexp matches what you want:

(?!.*msg-[-0-9]{4,16}\.html?$).*\.html?$

However AFAIK there isn't any place where bash supports Perl regexps. The =~ operator only supports extended regexps¹, which don't include zero-width lookahead assertions such as (?=…) and (?!…).

It is theoretically possible to convert a regexp with lookahaed assertions to one without, but the resulting regexp would be huge. It is much simpler to use two regexps:

[[ $string =~ \.html?$ && ! $string =~ msg-[-0-9]{4,16}\.html?$ ]]

_{¹ First there were basic regexps (BRE) (with several syntax variants), then came extended regexps (ERE) with more features (and again several syntax variants). Perl added yet more features, and many languages provide perl-compatible regexps (pcre). But bash sticks to ERE.}

What language are you using?

In general it sounds like you want something that matches the basic aspects of a domain, ruling out the possibility of a period other than the one that delinates the .tld.

#http://[^.]+\.(com|net|org)#i

If you don't want to match the protocal, maybe something like this.

#[^. ]+\.(com|net|org)#i

Your desire to handle multi-part TLD's will really screw this up, you will need to maintain a manual list of all the ones you want to match. The only alternative is to do DNS lookups to determine the listing type. There really isn't another way to extract subdomain data from the domain with a regular expression because by rights domains are actually just subdomains of some TLD (top level domain).

Edit: To match TLD's assuming they woudl have less than four characters, you can play around with something like this. You're going to have to work out what constitutes the start and end of a match. Are you requireing the presense of a protocal? Is this in a paragraph where somebody could type.a period out of context? If you give more details on the parameters we might be able to provide a more precise solution.

[^.]+((\.[^.]{0,3})+)