Regular expression to match number with Decimal separator and optional Thousands separator

Question

I need to validate if a number is valid with using decimal separator and thousand separators optionally. I need a regex, because the current code, that is not done by me uses a regex that is not working properly and I am aiming to fix it.

So the following combinations would be legal (Using . as decimal separator and , as thousand separator)

• 10000
• 100,000,000
• 100,000,000.345345
• 10000.689

But the following wouldn't be legal:

• 10000,000,000.34534

Basically I want numbers with a proper use of decimal and thousand separator or without them at all, but not invalid combinations. I looked around a lot, so far I found this post. Which has a great regex that matches perfectly when the numbers have decimal separator and thousand separator, but when I try to add the other options (numbers only with decimal separator, or number integers) I break the expression.

I decided that maybe I could capture groups matching the rules with or, so the number matches one expression or the other like this:

^([+-]?[0-9]{1,3}(,[0-9]{3})*(\.[0-9]+)?)|(((\d)*)+?(\.\d))|(\d*)$

The first group is the expression from the other post, the second I think covers numbers with a decimal separator and the last one are integers, but it is not working.

For example these numbers are not getting matched:

• 10000000.56
• 10000000

I think the issue it is happening because it always test for the first group, but I am not sure how to use the groups properly so it matches either of them. Also I think I am placing the -+ signs in the wrong place.

I did search a lot, and couldn't find one expression that worked properly. From the ones suggested:

From the Regex for number with decimals and thousand separator post

• ((\d){1,3})+([,][\d]{3})*([.](\d)*)? -> It wrongly captures 10000000. and 10,000,000.
• ^(?!0+\.00)(?=.{1,9}(\.|$))\d{1,3}(,\d{3})*(\.\d+)?$ -> it fails for 10000000
• /^(?!0+\.00)(?=.{1,9}(\.|$))(?!0(?!\.))\d{1,3}(,\d{3})*(\.\d+)?$/ -> it fails for 10000000
• ((\d){1,3})+([,][\d]{3})*([.](\d)*)? -> It fails for -100.03

This Can I use an OR in regex without capturing what's enclosed? post is not a duplicate, it explains something that could help me solve the issue, but it is not a duplicate, especially because I have issues also with the +- signs. Also my questions covers a problem that is not particular to me, this is a problem many people face, yet from the implementations I have found so far, none work.

From RegEx matching numeric values with or without thousand separators post

• ^-?([0-9]{1,3}\.?)+$ -> It fails for -1000 but not for and not for 100.00.3
• ^-?(?!0)(?:\d+|\d{1,3}(?:\.\d{3})+)$ -> It fails for -100.03

Answer 1

You may use this regex for validation:

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

RegEx Demo

It matches following cases:

• An integer number
• A floating point number
• A number with separators as , at 3rd place

Answer 2

The reason the second alternative isn't matching is because it only allows a single \f after the decimal point. That needs to be \d+.

Then you need to wrap everything between ^ and $ in a group, so all alternatives match the entire string.

You had lots of redundant parentheses. And \d* in the last alternative should be \d+, otherwise you'll allow a number that's completely empty or just a sign.

^[+-]?([0-9]{1,3}(,[0-9]{3})*(\.[0-9]+)?|\d*\.\d+|\d+)$

• ^ -> start of string
• [+-]? -> matches optional + or - char
• ([0-9]{1,3}(,[0-9]{3})*(\.[0-9]+)?|\d*\.\d+|\d+) -> whole group has to match [0-9]{1,3}(,[0-9]{3})*(\.[0-9]+) or \d*\.\d+ or \d+
  • [0-9]{1,3}(,[0-9]{3})*(\.[0-9]+) -> matches numbers with thousand separators and maybe decimal separator
  • \d*\.\d+ -> matches numbers with decimal separator, and maybe digits before the decimal
  • \d+ -> matches numbers without decimal separator
• $ -> end of string

DEMO