Regex: extract numbers between text

Question

currently I'm using such regex "(\d{4}\b)" in order to extract the numbers. Test string "test 125456 b", so the extract result is "5456".

I wish to get the same result "5456" under the string "test125456b".

I tried to use following regex

((?<!\d)(\d{4})(?!\d))

but it works if only 4 digits (not more) are noted between letters.

So, the aim is:

• extract only digits from the text
• extract only specific number of digits In this case 4) even in the text is given more
• digits (in this case 4) should be extracted backwards

Answer 1

To get the last four digits.

\d{4}(?=\D*$)

• \d{4} match the four digit character.
• (?=\D*$) Only if the four digits are followed by a zero or more non-digit characters and the end of the line boundary.
• So this matches the last 4 digits.

Answer 2

(\d{4}(?=[^\d]))

Use this. It'll look for 4 digits with a non-digit following.

Regex101