Question

I got a regex that fails on validating my input.

My regex: \d{1,5}([\.,]\d{0,2})?

It should validate square meters (decimal values) with a separator of either . or , and should allow up to five digits (and at least one) before the separator and up to two after it.

So it should accept:
1
1,0
1.0
12345
12345,10
12345.10

But not
.1
123456
12345,123

Answer 1

In the group you’re capturing, ([\.,]\d{0,2})?, you allow the numbers to appear between 0 and 2 times, however, the entire group is marked as optional per the ending ?. Because of this, the range should be set to {1,2} instead:

\d{1,5}([\.,]\d{1,2})?

If your input is specifically a number (and not a full sentence), I would also recommend adding a leading ^ and an ending $. This will force the regex to check from the start of the string to the end (respectively). The final regex should be:

^\d{1,5}([\.,]\d{1,2})?$

If you’re using this regex for more than validation and also want to view the matched values, you should change the current group that’s matching (the decimal portion) to a non-matching group (change ( to (?:) and then add parentheses around the full regex:

^(\d{1,5}(?:[\.,]\d{1,2})?)$