Regex with letter number and dash without leading and trailing dash

Question

Sorry if my question can be simple but, I'm blocked.

I was looking for a way to validate a regex that match several cases :

• Minimum 1 character (can be letter or number)
• Maximum 100 characters (can be letter, number and dash)
• Can't start with a dash
• Can't end with a dash
• Can't have 2 following dashes

I've tried this : ^[a-zA-Z0-9]{1}(?:([a-zA-Z0-9][-]{0,1}){0,98}[a-zA-Z0-9])?$

It works for almost every cases. Except those 2 cases :

• 0-1234 (dash on the second character)
• If I write 100 characters (0123456789[...]blablabla) then I insert dashes inside, it still validates the string even if I don't want to go over 100 characters

Can someone help me please ? Thanks a lot !

Answer 1

Here's just an alternative to Jan's already perfect solution.

^(?:[^\W_]|(?<=[^\W_])-(?=[^\W_])){1,100}$

It can be "decrypted" as: between 1 and 100 occurrences of either

• a letter or digit, or
• a dash preceded and followed by a letter or digit.

Answer 2

You are looking for lookaheads and another character class:

^(?!-)(?!.*-$)(?!.*--)[a-zA-Z0-9-]{1,100}$

See a demo on regex101.com.