My apologies you were right. I misunderstood the question. Yves
On Thu, 9 Jan 2020, 09:39 demerphq, <demer...@gmail.com> wrote:
> On Thu, 9 Jan 2020 at 05:49, Joseph He <joseph.he.2...@gmail.com> wrote:
> >
> > I think $str =~ /(\d+)\s(\d+)\s(??{$1*$2})/ should do it
> > My Perl version is v5.26.1
>
> I think you mean (??{ "$1*$2"}) which might work, but it will be error
> prone, (??{"(?$1)*$2") would be better, but both will be slow, as each
> time a new pattern willbe compiled.
>
> /(\d+)\s(\d+)\s(\1*\2)/
>
> just works, and does not recompile the pattern over and over. Look for
> "back references" in perlre.
>
> Yves
>
