Thread: BUG #8679: Error in regex function

The following bug has been logged on the website:

Bug reference:      8679
Logged by:          Andrzej
Email address:      spmpro@pochta.ru
PostgreSQL version: 9.2.0
Operating system:   Ubuntu
Description:

Hi, I make command select regexp_replace('rewqe ','(?<=[q]{1})[e]{1}(?=[\-
$]+)','11');
and he return error 'invalid regular expression: quantifier operand
invalid', but regex is correct (check by http://gskinner.com/RegExr/). This
error repeat in another regex function (regexp_matches,
regexp_split_to_array).


But command select regexp_replace('rewqe ','[e]{1}(?=[\- $]+)','11') work
good. May be, regex construction (?<=\pattern\) is not support?

spmpro@pochta.ru writes:
> May be, regex construction (?<=\pattern\) is not support?

It is not.  What we support is documented at
http://www.postgresql.org/docs/9.2/static/functions-matching.html#FUNCTIONS-POSIX-REGEXP

I have no idea what "(?<=" is supposed to mean --- it's not a standard
regexp construct, for sure.  In general, "(?" is used to introduce
non-POSIX extensions that are specific to particular regexp
implementations.  There's some commonality there, but you should never
assume that such things are portable.

            regards, tom lane

On Fri, December 13, 2013 18:40, Tom Lane wrote:
> spmpro@pochta.ru writes:
>> May be, regex construction (?<=\pattern\) is not support?
>
> It is not.  What we support is documented at
> http://www.postgresql.org/docs/9.2/static/functions-matching.html#FUNCTIONS-POSIX-REGEXP
>
> I have no idea what "(?<=" is supposed to mean --- it's not a standard

FWIW, perl has these; see http://perldoc.perl.org/perlre.html (search for "Look-Around Assertions" ):

   (?<=pattern)   A zero-width positive look-behind assertion

   (?<!pattern)   A zero-width negative look-behind assertion.


It would certainly be nice if these would implemented in postgres...