Обсуждение: regexp_replace weirdness amounts to a bug?

Hello,

The following surprised me enough to think it might be a bug:
(17devel)

select
    regexp_replace('Abc Def'
   , '([a-z]) ([A-Z])'
   , '\1 ' || lower('\2')  );

regexp_replace
----------------
  Abc Def
(1 row)

-- 'Abc Def' got
-- 'Abc def' expected

What do you think?

Thanks,

Erik Rijkers

Hi Erik,

The regexp doesn't match your string because you're not allowing for
any repeat characters, try adding a '+'.

On Wed, 16 Aug 2023 at 09:07, Erik Rijkers <er@xs4all.nl> wrote:
>
> Hello,
>
> The following surprised me enough to think it might be a bug:
> (17devel)
>
> select
>     regexp_replace('Abc Def'
>    , '([a-z]) ([A-Z])'
>    , '\1 ' || lower('\2')  );
>
> regexp_replace
> ----------------
>   Abc Def
> (1 row)
>
> -- 'Abc Def' got
> -- 'Abc def' expected
>
> What do you think?
>
> Thanks,
>
> Erik Rijkers
>
>
>

On 2023-Aug-16, Erik Rijkers wrote:

> Hello,
> 
> The following surprised me enough to think it might be a bug:
> (17devel)
> 
> select
>    regexp_replace('Abc Def'
>   , '([a-z]) ([A-Z])'
>   , '\1 ' || lower('\2')  );
> 
> regexp_replace
> ----------------
>  Abc Def

What's happening here is that the lower() is applying to the literal \2,
and the expansion of \2 to 'D' occurs afterwards, when lower() has
already executed.  Note this other example, where the literal part of
the replacement string is correctly lowercased:

select
   regexp_replace('Abc Def'
  , '([a-z]) ([A-Z])'
  , '\1 ' || lower('D\2D'));
 regexp_replace 
────────────────
 Abc dDdef
(1 fila)

I don't know how to achieve what you want.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
#error "Operator lives in the wrong universe"
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