Question

I am looking for a regex to create a string of characters with the following criteria:

• Can be variable length (max 30 characters)
• Can have only alphanumeric (a-z,A-Z) and Numeric characters(0-9)
• Can have only these special characters “-“,”.” anywhere in the string
• Must start with only alphanumeric or numeric, not special characters
• Must be at least 5 characters

The “badge” string will need to be used in the url of the site, any advice on whether this string would be alright would be appreciated.

Thank you

Answer 1

RegExp’s do not create strings they are used to validate or match them. Is that what you mean?

A RegExp to validate a string against your constraints would be

  /^[a-z0-9][-,\.a-z0-9]{4,29}$/i

Explanation :

   /^                  Start of string
   [a-z0-9]            One character in the set a-z or 0-9 
                       (A-Z also valid since we specify flag i at the end
   [-,\.a-z0-9]{4,29}  A sequence of at least 4 and no more than 29 characters
                       in the set. Note . is escaped since it has special meaning
   $                   End of string (ensures there is nothing else
   /i                  All matches are case insensitive a-z === A-Z