I have a list a domain names that I need to create snort rules for. Inserting text into a line is not too complicated but what needs to be done here is.

If I have a domain
foo.com

It need to be put into rule first here:
msg:"watch for domain foo.com";

Then inserted again further down the rule but modified first:
content:"|03|foo|03|com|00|";

The number is a count of the number of characters of each part of the domain. foo contains 3 characters so it is preceded by |03|. There will always be a |00| at the end.

The tricky part is the domain could have any number of sections:
foo.com
foo.foobar.com
foo.foobar.foo.com

So if I had foo.foobar.com the end result would be
blah blah blah blah -> blah blah (msg:"watch for domain foo.foobar.com"; blah; blah; content:"|03|foo|06|foobar|03|com|00|"; blah; blah;)

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