Question

I’m trying to validate usernames in PHP using preg_match() but I can’t seem to get it working the way I want it. I require preg_match() to:

1. accept only letters or numbers at the beginning and end of the string
2. accept periods, dashes, underscores, letters, numbers
3. must have a length between 5-20 characters

preg_match('/^[a-zA-Z0-9]+[.-_]*[a-zA-Z0-9]{5,20}$/', $username)

Answer 1

Break down the requirements into smaller pieces and you’ll see that it becomes a lot easier:

• The first character must be 1 letter or number
• The middle characters must be a period, dash underscore, letter or number
• The last character must be a a letter or number
• As the first and last segments must be 1 character, the middle must be 3 to 18

~^[a-z0-9]{1}[a-z0-9._-]{3,18}[a-z0-9]{1}$~i