Sorry to recommence this rubique but I have a similar question.
My current robots.txt is this.
It has removed all my problems with robots but given me another one. My website traffic has very much dropped.
I noticed that google and yahoo were have had 90% of my search engine. And I truely only need to stop a total of 4 or 5 robots. (It does not appear to be worthy of the problem to make a dynamic script.)
Is it possible to do this in a robots.txt
User-agent: alexa, askjeeves, etc, etc
User-agent: another bot.
IE: Disallow the robots directly that i do no want and let the others come in.