SPUG: minimal unmatching regex

Joshua Juran jjuran at gmail.com
Tue Aug 18 21:58:44 PDT 2009

On Aug 18, 2009, at 12:04 PM, Michael R. Wolf wrote:

> Question:
> What's the smallest (comprehensible) regex that's guaranteed to  
> fail against all input?
> Motivation:
> I'm creating a lab for perl classes.  I want to provide the stub of  
> a script that compiles, but always fails to match.  Unfortunately,  
> the obvious minimal RE of // matches *everything*.

I don't know the syntax of the top off my head, but here's the logic:

* beginning of string (not strictly necessary, but a useful  
* negative lookahead assertion for X
* X


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