Extract third level of folder structure stored in MySQL field - mysql

Question

I'm using the following regex (https://regex101.com/r/Kt9sNj/1) in PHP to get all the files in the third level of a directory:
/^(\/[^\/]*){1,4}\/?$/m
Then if I have the following data:
/home/myuser/folder_example/first_file.txt
/home/myuser/folder_example/second_file.txt
/home/myuser/folder_example/third_file.txt
I get:
first_file.txt
second_file.txt
third_file.txt
I try to use this in a MySQL query that contains an array of a json object.
My Query is:
SELECT data->'$.files' AS File
FROM table
WHERE user = 'myuser';
And I get:
["/home/myuser/folder_example/first_file.txt","/home/myuser/folder_example/second_file.txt","/home/myuser/folder_example/third_file.txt"]
But when I use that regex on my sql query:
SELECT data->'$.files' AS File
FROM table
WHERE user = 'myuser'
AND data->'$.files' REGEXP '^(\/[^\/]*){1,4}\/?$';
I need to get this (all files under that directory):
["first_file.txt","second_file.txt","third_file.txt"]
It doesn't work. Do you know why?

Answer 1

The function REGEXP returns 1 if the pattern matches and will return the full match as the pattern does match the example strings.
In your pattern you are repeating a capturing group, which will capture the last value of the iteration in group 1, but it still contains a leading forward slash that you don't want in the output.
What you might do is match the first /, and then use a quantifier {3} to repeat exactly 3 times a part ending on a / using a non capture group.
Then capture the filename in group 1, and refer to that group using '$1' in the replacement using REGEXP_REPLACE
^/(?:[^/]*/){3}(\S+\.[^.\s]+)$
Regex demo | Mysql with replace demo