Regex validation string 4th and 6th special character optional validations

Question

I am trying to make a regex validation and the condition is that, whatever I have typed in 4th character it should same as 6th character from special character(-.) dash or dot

So if I have typed 4th character as - then 6th also must be - and if dot then should be dot.

Also these character can be optional. So If the string don't have 4th character as special character(-.) then 6th also should not be have special character

Note: First 3 character must be number and 5th character also number

For example:

123-3- valid
123.4. valid
123-6. invalid
123.7- invalid
1234 valid
12-34 invalid
123.4 invalid

What I am trying is below

"""(\d{3})[\-.]*(\d{1})[\-.]${'$'}"""

Any help will be appreciated!!

Answer 1

You can write the pattern with a single optional capture group and an optional backreference, or match 4 digits.

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

• ^ Start of string
• (?: Non capture group for the alternation
  • \d{3}([-.])\d\1 Match 3 digits, capture one or - or . and then match a digit followed by the same captured char using a backreference \1
  • | Or
  • \d{4}
• ) Close non capture group
• $ End of string

Regex demo

Or a bit shorter, matching 3 digits followed by either a digit between the same . or - , or just a single digit:

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

Regex demo