regex repetitive pattern with monetary amount-CodePudding

(?:[.,]?\d{3})* this is a part of a monetary amount pattern which match the thousand separator and the 3 digits after. The thousand separator can either be ., , or nothing

But how to make it repetitive? If the first thousand separator is . then the rest should also be .

CodePudding user response：

You can use a capture group with a repeating backreference:

^(?:\d{4,}|\d{1,3}(?:([,.])\d{3}(?:\1\d{3})*)?)$

Explanation

^ Start of string
(?: Non capture group for the alternatives
- \d{4,} Match 4 or more digits
- | Or
- \d{1,3} Match 1-3 digits
- (?: Non capture group
  - ([,.])\d{3} capture either a . or comma in group 1
  - (?:\1\d{3})* Optionally repeat the backreference to group 1 (the same char) followed by 3 digits
- )? Close the non capture group and make it optional (to also match 1-3 digits)
) Close the non capture group
$ End of string

See a regex demo.

CodePudding user response：

Take it block by block: the begining the middle and the end. Then use a or to match the numbers < 1000.

((\d{1,3}\.){,1}(\d{3}\.)*(\d{3})|(\d{1,2))