Regular expression to match smallest only

Question

I have a expression like c.{0,2}?mand a string like "abcemtcmncefmf". Currently it will matches three substrings: cem, cm and cefm (see here). But I like to match only the smallest of this, in this case, cm.

My problem is that I don't have a global match support, only the first match, because I'm using MariaDB REGEXP_SUBSTR() function. My current solution is a stored procedure that I created to solve my problem. But it is 10 times slower than just a regular expression for simple cases.

I too tried do something like: (cm|c.{0,1}?m|c.{0,2}?m), but it doesn't worked because it will match first of any group patterns, instead of try one by one in all subject string.

I know that regular expressions (PCRE) have some black magic features, but I don't found nothing to solve my problem.

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• Note: I'm yet using non-greedy pattern (.{0,2}?) on my current pattern;
• The question Regular expression to find smallest possible match don't is my problem;

Answer 1

You can simply use an alternation in a branch reset group:

/^(?|.*(cm)|.*(c.m)|.*(c..m))/s

(The result is in group 1)

or like this:

/^.*\Kcm|^.*\Kc.m|^.*\Kc..m/s

The first successful branch wins.