Max length ignoring one character in Regex

Question

I have a Regex Which allows up to 6 decimals("." is the decimal separator)

/^\d*[.]?\d{0,6}$/

I also want to put max length condition so that user can only enter 12 digits and max length should exclude "." how do I do that with Regex.

Answer 1

You could use a positive lookahead to check for either a number with a decimal place with up to 6 digits after it or a string of 12 digits) and then match up to 13 characters in total:

^(?=\d*\.\d{0,6}$|\d{1,12}$).{1,13}$

For this input, the 2nd and 5th values will match:

1234567890123
123456.789012
12345.6789012
1234567.890123
12345.67890

Demo on regex101