John P. Linderman wrote:
> Using what is to me the more obvious [0-9] pattern takes almost 50 times as
> long as using the [[:digit:]] pattern. Seems very strange.

Thanks for reporting that. In general, patterns like [a-z] can be much slower 
than [[:lower:]] due to poorly-thought-out POSIX interfaces. However, [0-9] is a 
special case: we can optimize such patterns safely if both ends are ASCII 
digits. I installed the attached patch to Gnulib to do that; it fixes the 
performance glitch you noticed, at least for me.