[Pharo-users] Non-greedy RegEx?

Richard O'Keefe raoknz at gmail.com
Tue Feb 5 19:45:28 EST 2019


PCRE has exponential worst-case time.  See for example
https://www.regular-expressions.info/catastrophic.html
but searching for PCRE exponential time or worst case
will find more.  That's not the problem.  The problem
is that it isn't *obvious* which regexps are safe and
that people are taught that regular expressions can be
matched in linear time, which is sort of the point of
them.  But PCRE patterns *aren't* regular expressions.


On Wed, 6 Feb 2019 at 04:54, Pierce Ng <pierce at samadhiweb.com> wrote:

> On Wed, Feb 06, 2019 at 12:26:00AM +1300, Richard O'Keefe wrote:
> > Please DON'T move to PCRE.
> > "Outside world standards"?  There are so many.
> > There are two important things to know about
> > PCRE: (1) it is a popular open source regexp
> > library for Perl-style regexps, (2) because of
> > that, it is prone to truly horrendous performance
> > problems.  There are alternatives, such as re2,
> > https://github.com/google/re2 ,
> > which are not subject to PCRE's intrinsic
> > performance pathologies.  As it happens, re2
> > supports *? +? and ??.
>
> Can you share some examples of PCRE's bad performance?
>
> Pierce
>
>
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