Match exactly one of each from set of characters

Question

I am trying to match a specific set of characters but 1 and only 1 of each.

For example if the set is [abcd], I want to match string containing these exact characters in any order.

abcd  - true
bcad  - true
abc   - false (need all characters)
abbd  - false
abcdd - false

From what I understand so far there is no easy way to achieve this with RegEx but no answer was conclusive enough.

Answer 1

I would think of capturing and using a lookahead to check if the same character is not ahead.

\b(?:([abcd])(?!\w*?\1)){4}\b

• (?: opens a non capture group for repetition
• \b matches a word boundary
• ([abcd]) captures one of [abcd]
• (?!\w*?\1) checks if the captured character is not ahead with any amount of \w in between
• {4}\b 4 times until another word boundary

See demo at regex101   (works only, if a lookahead is available in your regex flavor)