Regex for alphanumeric string including at least one digit

user_1344855 0
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I'm looking for a regex with at the conditions:

  • a) minimum 13 alphanumeric characters
  • b) maximum 17 alphanumeric characters
  • c) and at least 1 digit.

This regex fulfils a) and b). How can it fulfil also condition c)?

^[a-zA-Z0-9]{13,17}$

Example input texts:

# matching
123456789abcd
123456789abcdef
123456789abcdefg

# no match: too long
123456789abcdefgef

# no match: no digit
abcdefghijklmno

# no match: not alphanumeric only
123456789@abcdefg

The flavor is Java 8.

regex
2 Answers

It sounds like you are trying to make a password checker. I suggest that you NOT try to do it all in one single regex.

Check your input against two different regexes that must both match:

^[a-zA-Z0-9]{13,17}$        # 13-17 alphanumerics

and

[0-9]                       # at least one digit

Compared to this suggestion from another answer...

^(?=[a-zA-Z]*[0-9])(?=[0-9]*[a-zA-Z])[[:alnum:]]{13,17}$

... it's so much clearer that way, and easier to change when your rules change in the future.

user_84540

Regex:

^(?=[a-zA-Z]*[0-9])(?=[0-9]*[a-zA-Z])[[:alnum:]]{13,17}$

Explanation: ^(?=[a-zA-Z]*[0-9]) - Lookahead for zero or more letters followed by a number, somewhere in the string, note this is faster than the (?=.*[0-9]) suggested in another answer.

(?=[0-9]*[a-zA-Z]) - as above but looking for at least one letter (I assume you want this, although it wasn't specified in your answer.

[[:alnum:]]{13,17}$ - The actual match bit; this is just your regex ([a-zA-Z0-9]{13,17}$) in short-hand.

If it's more likely that a string will not have a letter then swapping the order of the lookaheads should make it faster. The current order would be best if a missing number is the most likely fail condition (as the regex will fail faster).

See https://www.rexegg.com/regex-lookarounds.html#password for a detailed explanation.

Regex Tests

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