Posted by Anno Siegel on 09/15/05 10:51

www.douglassdavis.com <doug@douglassdavis.com> wrote in comp.lang.perl.misc:
>
> Anno Siegel wrote:
> > www.douglassdavis.com <doug@douglassdavis.com> wrote in comp.lang.perl.misc:
> > > I am using the preg_match function (in PHP) that uses perl regular
> > > expressions. Apparently I don't really understand regular expressions
> > > though. Could some one explain this?
> > >
> > > If this is the regular expression
> > >
> > > /^\s*(\d+\.\d+)|(\.\d+)|(\d+)\s*$/
> > >
> > > How does this:
> > >
> > > 40:26:46.302N 79:56:55.903W
> > >
> > > match? I thought when I added the ^ and $ that meant it had to match
> > > the whole thing? It seems to only be matching .302
> >
> > Concatenation binds tighter than alternation. So the first alternative
> > is anchored to the left margin and the last one is anchored to the right
> > margin. The middle one isn't anchored and matched what it can.
> >
>
> That makes sense. Thanks. This seems to work:
>
> /^\s*((\d+\.\d+)|(\.\d+)|(\d+))\s*$/

Yes, but it messes up the capturing parentheses.

/^\s*(?:(\d+\.\d+)|(\.\d+)|(\d+))\s*$/

Anno
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