How can I use a Regular Expression to return a number of numbers at the end of a string of digits

Question

I have a string of digits that could vary in length and I want to return only the last 4 digits. Would I use a positive lookback? And use the $ to anchor to?

Answer 1

If your string can be ANY length and you want to match the cases when you have 0 to 3 charaters you should use:

\d?\d?\d?\d?$ 

or, if the regex engine understands it:

\d{0-4}$

Answer 2

use this regular expression \d{4}$