Regex to validate password containing a digit rejects string with multiple digits

Question

I have the following pattern to validate a password form (not ideal, I know, but it’s for an assignment).

/^(?=[a-zA-Z0-9]{8,})(?=[a-zA-Z]*[0-9][a-zA-Z]*$)[a-zA-Z0-9]+$/

My idea is, I need the password to be at least 8 letters long, and include at least one number and one letter. It also cannot include any special characters.

It accepts password1 as a password, but it does not accept password12 as a password. How can I fix this?

[Reference - Password Validation](https://stackoverflow.com/questions/48345922/reference-password-validation/) may help you. — ctwheels, Apr 05 '18 at 20:58
Why do you need the `(?=[a-zA-Z]*[0-9][a-zA-Z]*$)`? It means that the whole password must contain exactly one digit between any number of letters from start to finish. — Sebastian Simon, Apr 05 '18 at 20:58
Thanks for the link ctwheels, i'm aware of this but it's for a bit of coursework where the submission needs to include a password that is only 8 letters, include 1 digit and 1 letter but no special characters. I'm not sure Xufox, i'll remove it and test. — , Apr 05 '18 at 21:01
@JohnDoi2021 Don’t just remove it. Try this here: `/^(?=[a-zA-Z]*[0-9])(?=[0-9]*[a-zA-Z])[a-zA-Z0-9]{8,}$/`. — Sebastian Simon, Apr 05 '18 at 21:01

score 0 · Accepted Answer · answered Apr 05 '18 at 21:10

Your regex is close but has some issues:

The portion (?=[a-zA-Z]*[0-9][a-zA-Z]*$) means “assert that exactly one digit ([0-9]) exists from start to finish ($) with any number of letters around it (2× [a-zA-Z]*)”.

Instead, you want something like this:

/^(?=[a-zA-Z]*[0-9])(?=[0-9]*[a-zA-Z])[a-zA-Z0-9]{8,}$/

Here, (?=[a-zA-Z]*[0-9]) and (?=[0-9]*[a-zA-Z]) mean “assert that a digit exists after any number of letters” and “assert that a letter exists after any number of digits” respectively.

After that, you can simply match [a-zA-Z0-9]{8,}.

Regex to validate password containing a digit rejects string with multiple digits

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