I need a specific regex pattern for Java and Javascript

Question

I need a regular expression with following conditions:

min 5 characters, no max characters (only letters and numbers)
must contain minimum 4 letters
must contain minimum 1 number

E.g. of correct results: root1 1root ro1ot Roo11t etc...

Currently I have the pattern ^(?=.*\d{1,})(?=.*[a-zA-Z]{4,}).{5,}$

But this seems to also accept special characters...?

Thanks a lot!

I'm not even sure the criteria can be checked with regex, it's too dynamic. — Terry
– Terry, Commented Apr 23, 2013 at 12:55
ro1ot seems not matches ^(?=.*\d{1,})(?=.*[a-zA-Z]{4,}).{5,}$ — johnchen902
– johnchen902, Commented Apr 23, 2013 at 12:57

Loamhoof · Accepted Answer · 2013-04-23 13:03:58Z

6

.{5,} that's why it allows special characters (dot = everything (except line feeds and such in fact)). Change it to [a-z0-9]{5,} or whatever you want.

Note: (?=.*\d{1,})(?=.*[a-zA-Z]{4,}) only check the 2th and 3rd requirement, but don't say anything about the wanted nature of the characters.

Edit:
Other problem: your specification says "at least 4 letters" but your regex says "4 consecutive letters". Also, use lazy quantifiers.

/^(?=.*?\d)(?=(?:.*?[a-z]){4})[a-z0-9]{5,}$/i

(?=.*?\d) => you don't need to check for more than 1 number, once you found it, stop.
(?=(?:.*?[a-z]){4}) => changed to find 4 letters, but not consecutive. Also, added an insensitive case modifier i at the end (in JS, in Java you're not declaring it the same way).

edited Apr 23, 2013 at 13:03

answered Apr 23, 2013 at 12:51

Loamhoof

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2 Comments

Loamhoof Over a year ago

@Zwammer seen another problem also (and making some improvement). Editing

Zwammer Over a year ago

Thanks! This works like a charm. Regex can be quite a mystery for the inexperienced :D

johnchen902 · Accepted Answer · 2013-04-23 13:05:11Z

1

I know this is ugly, but this appears to work:

^[a-zA-Z0-9]*(([a-zA-Z]{4,}\d)|([a-zA-Z]{3,}\d[a-zA-Z]+)|([a-zA-Z]{2,}\d[a-zA-Z]{2,})|([a-zA-Z]+\d[a-zA-Z]{3,})|(\d[a-zA-Z]{4,}))[a-zA-Z0-9]*$

answered Apr 23, 2013 at 13:05

johnchen902

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