How to capture recursive groups in a regex? - regex

Question

I am trying to capture a pattern which can appear multiple times in a regex in different groups. The pattern which can appear multiple times is :
(\b\\d{4}\\s*\\d{4}\\s*\\d{4}\\s*\\d{4}\b\\s*)
Please see complete test#here!
The expected output should be :
Full Match:
Group1:1111 1111 1111 1111
Group2:2222 2222 2222 2222
... GroupN...
how can this be achieved ?

Answer 1

If I understand the problem correctly, we would be wishing for matching a four-digits and space pattern being repeated three times, followed by another four-digits, and we can likely start with a simple expression such as:
(\d{4}\s)\1\1(\d{4}\s?)
Demo 1
Or if we would be matching a four-digits pattern four times, and space three times, we would likely start with this expression:
(\d{4})(\s+)\1\2\1\2\1
Demo 2
RegEx Circuit
jex.im visualizes regular expressions:

Answer 2

Use:
(?:<select\b|\G).*?(\b\d{4}(?:\s*\d{4}){3}\b)(?=.*?</select>)
Demo
Explanation:
(?: # non capture group
<select\b # literally
| # OR
\G # restart from previous match position
) # end group
.*? # 0 or more any character, you may use [\s\S]*?
( # start group 1
\b # word boundary
\d{4} # 4 digits
(?: # non capture group
\s* # 0 or more spaces
\d{4} # 4 digits
){3} # end group, may appear 3 times
\b # word boundary
) # end group 1
(?= # lookahead, make sure we have aftre:
.*? # 0 or more any character
</select> # end tag
) # end lookahead
Sample code (php):
preg_match_all('~(?:<select\b|\G).*?(\b\d{4}(?:\s*\d{4}){3}\b)(?=.*?</select>))~', $html, $matches);
print_r($matches[1]);