Re: [Gnu-arch-users] Preventing matches in regular expressions

[Andrew Suffield]

On Mon, Aug 09, 2004 at 03:29:53PM -0400, Aaron Bentley wrote:
> That would add or update the regexes in the .arch-inventory.  But since 
> backup is tried before unrecognized, the rule for backup must match 
> every zip file except 'fox.zip'
> 
> Here's what I've finally come up with, using the example 'fox.zip':
> 
> backup ^(.{0,2}|.{4}.*|[^f]..|.[^o].|..[^x])\.zip$

Yes, that's right. It's an old and rather evil trick.

> But man, oh man, that's an ugly regex, and it'll only get less readable 
> with longer filenames and multiple filenames.
> 
> Does anyone know a better general solution?

Well, you can implement regexp extensions that construct these
things. They can get a bit memory-hungry though.

More normally you just step outside the bounds of regexps though. Perl
does it by having regexps that aren't; perlre cannot be expressed as
an NFA, although it still uses one to do *most* of the work.

-- 
  .''`.  ** Debian GNU/Linux ** | Andrew Suffield
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