You are right, I also found the same behaviour when using e.g the UNIX sed
command.
Ingolf
On Mon, Aug 23, 2021 at 4:24 PM Francisco Olarte <fola...@peoplecall.com>
wrote:
> Ingolf:
>
> On Mon, Aug 23, 2021 at 2:39 PM Markhof, Ingolf
> <ingolf.mark...@de.verizon.com> wrote:
> > Yes, When I use (\1)? instead of (\1)+, the expression is evaluated
> quickly, but it doesn't return what I want. Once a word is written, it is
> not subject to matching again. i.e.
> > select regexp_replace( --> remove double entries
> > 'one,one,one,two,two,three,three',
> > '([^,]+)(,\1)?($|,)',
> > '\1\3',
> > 'g'
> > ) as res;
> >
> ...
> > Honestly, this behaviour seems to be incorrect for me. Once the system
> replaces the first two 'one,one,' by a single 'one,', I'd expect to match
> this replaced one 'one,' with the next 'one,' following, replacing these
> two by another, single 'one,', again...
>
> I think your expectation is misguided. All the regexp engines I've
> used do it this way, when asked to match "g"lobally they do
> non-overlapping matches, they do not substitute and recurse with the
> modified string.
>
> Also, your way opens the door to run-away or infinite loops (
> rr('a','a','aa','g') or rr('a','a','a','g'), not to speak of
> r('x','','','g') ). Even a misguided r(str, '_+','_','g'), used
> sometimes to normalize space runs and similar things, can go into a
> loop.
>
> Francisco Olarte.
>
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