Multiline regex match in MariaDB/Mediawiki - sql

Question

I am trying to match text (contained in a Mediawiki template) in multiple lines via the Replace Text extension in MW 1.31, server running MariaDB 10.3.22.
An example of the template is the following (other templates may exist on the same page):
{{WoodhouseENELnames
|Text=[[File:woodhouse_999.jpg|thumb|link={{filepath:woodhouse_999.jpg}}]]Αἰακός, ὁ, or say, son of Aegina.
<b class="b2">Of Aeacus</b>, adj.: Αἰάκειος.
<b class="b2">Descendant of Aeacus</b>: Αἰακίδης, -ου, ὁ.
}}
Above and below could be other templates, with varying number of line breaks I.e.
{{MyTemplatename
|Text=text, text, text
}}
{{WoodhouseENELnames
|Text=text, text, text
}}
{{OtherTemplatename
|Text= text, text, text
}}
There are varying number of lines and/or line breaks within the template. I want to match the full template and delete it; that is match from {{WoodhouseENELnames to the closing }} but without matching any templates further down, that is, stop matching if further {{ are encountered.
The closest I got was using something like:
Find
({{WoodhouseENELnames\n\|Text=)(.*?)\n+(.*?)\n+(.*?)\n+(.*?)(\n+}})
And adding/removing (.*?)\n+ in the regex to match cases with more or less lines. The problem is that this expression might inadvertently match other templates following this one.
Is there a regex that would match all possible text/line breaks contained within the template (in a lazy way, as there may be other templates below and above) in the same page? The templates are delimited by opening {{ and closing }})?

Answer 1

Edited to clear up any confusing
This is a recursion simulation for use on
Java, Python style engines that do not support function calls (recursion)
(?s)(?={{WoodhouseENELnames)(?:(?=.*?{{(?!.*?\1)(.*}}(?!.*\2).*))(?=.*?}}(?!.*?\2)(.*)).)+?.*?(?=\1)(?:(?!{{).)*(?=\2$)
Recursion Simulation demo
Just check matchs for result
This is real recursion for use on Perl, PCRE style engines
(?s){{WoodhouseENELnames((?:(?>(?:(?!{{|}}).)+)|{{(?1)}})*)}}
Recursion demo
Note that Dot-Net is done differently and is not included here

Answer 2

I can only think of a brute-force, iterative approach using a recursive query.
The idea is to walk through the string, starting at the first occurence of string part '{{WoodhouseENELnames'. From there on, we can set a counter that keeps tracks of how many opening and closing brackets were met. When the count reaches 0, we know the pattern is exhausted. The final step is to rebuild a string that retains the parts prior to and after the pattern.
For this to work, you need a unique column to identify each row. I assumed id.
with recursive cte as (
select
n_open n0,
n_open n1,
1 cnt,
mycol,
id
from (select t.*, locate('{{WoodhouseENELnames', mycol) n_open from mytable t) x
where n_open > 0
union all
select
n0,
n1 + 2 + case when n_open > 0 and n_open < n_close then n_open else n_close end,
cnt + case when n_open > 0 and n_open < n_close then 1 else -1 end,
mycol,
id
from (
select
c.*,
locate('{{', substring(mycol, n1 + 2)) n_open,
locate('}}', substring(mycol, n1 + 2)) n_close
from cte c
) x
where cnt > 0
)
select id, concat(substring(mycol, 1, min(n0) - 1), substring(mycol, max(n1) + 1)) mycol
from cte
group by id
Demo on DB Fiddle
Set-up - I added string parts before and after the pattern (including double brackets for extra fun):
create table mytable(id int, mycol varchar(2000));
insert into mytable values (
1,
'{{abcd{{WoodhouseENELnames
|Text=[[File:woodhouse_999.jpg|thumb|link={{filepath:woodhouse_999.jpg}}]]Αἰακός, ὁ, or say, son of Aegina.
<b class="b2">Of Aeacus</b>, adj.: Αἰάκειος.
<b class="b2">Descendant of Aeacus</b>: Αἰακίδης, -ου, ὁ.
}} efgh{{'
);
Results:
id | mycol
-: | :------------
1 | {{abcd efgh{{

Answer 3

MariaDB uses the PCRE-Regex engine.
If you can assure, that
the opening tag of your template ({{WoodhouseENELnames) starts on a new line
the closing tag of your template (}}) starts on a new line
no other closing tags (}}) in between starts on a new line, the follwoing Regex will do:
(?ms)^{{WoodhouseENELnames.+?^}}
Description:
(?ms) thells the regex that ^ matches any linebreak in the text and that . also matches newlines.
Then serach for your opening tag on a new line.
Search for the shortest possible string including any character (also newlines) up to
a closing tag (}}) on a new line.
If you want to capture the match, enclose the regex within (and )
EDIT:
As The PCRE2 supports recursive patterns, the follwing, more complexe regex will match, regardless of the beginnig-of-line-constraints above:
(?msx)
({{WoodhouseENELnames # group 1: Matching the whole template
( # group 2: Mathing the contents of the Template, including subpatters.
[^{}]* # Search zewro or more characters except { or }
{{ # The beginning of a subpattern
( # Containg if:
[^{}]++ # Search zewro or more characters except { or }
| (?2) # or the recursive pattern group 2
)* # Zero or more times
}} # The closing of the subpattern.
[^{}]* # Search zewro or more characters except { or }
)
}}
)
Cave-at: Doesn't cater for single { or } within the templates.
EDIT 2
I hate giving up before the job is done :-) This regex should work regardless of all contstraints above:
(?msx) # Note the additional 'x'-Option, allowing free spacing.
({{WoodhouseENELnames # Searcdh group 1 - Top level template:
( # Search group 2 - top level template contents:
( # Search-group 3 - Subtemplate contents:
[^{}]* # Zero or more characters except { or }
| {(?!{) # or a single { not follwed by a {
| }(?!}) # or a single } not follwed by a }
)* # Closing search group 3
{{ # Opening subtemplate tag
( # Search group 4:
(?3)* # Reusing serach group 3, zero or more times
| (?2) # or Recurse search group 2 (of which, this is a part)
)* # Group 4 zero or more times
}} # Closing subtemplate tag
(?3)* # Reusing search group 3, zero or more times
) # Closing Search group 2 - Template contents
}} # Top-level Template closing tag
) # Closing Search group 1
The last two solutions are based on the PCRE2 documentation