# Q5a · Password regex

Subject: Natural Language Processing

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/nlp/#tee/papers/legacy-r23/q5a

Canonical: https://deep-learning-study-room.vercel.app/read/nlp/tee/papers/legacy-r23--q5a/

Previous examination · complete worked answers

**Question. Write a regex for an 8–15 character password containing letters and digits, at least one uppercase letter and at least one special character from !%@\*, with no other characters.** [10 marks]

### Answer

`^(?=.{8,15}$)(?=.*[A-Z])(?=.*[0-9])(?=.*[!%@*])[A-Za-z0-9!%@*]+$`

| Part | Purpose |
| --- | --- |
| (?=.{8,15}$) | Length8–15 |
| (?=.\*[A-Z]) | At least one uppercase; this also meets the letter requirement |
| (?=.\*[0-9]) | At least one digit |
| (?=.\*[!%@\*]) | At least one permitted special |
| [A-Za-z0-9!%@\*]+ | Only permitted characters, including lowercase if desired |

Use full-string matching. Abcdef1! passes; abcdef1! fails uppercase, Abcdefgh fails digit/special, Abc1! is too short, Abcdef1# contains forbidden #. A lowercase character is not separately required by the printed conditions.