RegEx for N digits always starting with 2

Question

I want to validate these rules:

1)Only numbers

2)Must have 13 digits

3)Always start with number 2

4)May have dots after the first 8 digits, 2 digits and before last digit like:

(XXXXXXXX.XX.XX.X)

Example:

2437313600001 - 23610579.00.03.1

So far I have this

^([0-9]-?){13}$

How do I solve this problem?

Answer 1

You can use this regex,

^2\d{7}(?:\.?\d){5}$

Explanation:

• ^ - Start of string
• 2 - Start first character with 2 only
• \d{7} - Next seven characters can be any digits
• (?:\.?\d){5} - Next five characters can be any digits but they can be preceded by an optional dot before them
• $ - End of string

Regex Demo