Regex to match mixed case words

Question

I want to write a regex which will match any word consisting of 8 characters and these characters should belong to the charset: [A-Za-z0-9].

However, they should consist of at least one character from each of the 3 charsets (uppercase, lowercase and digits).

This is the regex I am using:

^[a-zA-Z0-9]{8}$

however, this will match examples like:

09823983
language
mainMenu

but I want to match words like:

uXk3mHy9

how can I do this using a regex?

kev · Accepted Answer · 2012-11-16T05:55:45.283

5

You can use three look-aheads in front of your regex:

^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])[a-zA-Z0-9]{8}$

edited Nov 16 '12 at 05:55

answered Nov 16 '12 at 05:27

kev

you don't need the trailing `.*` on your look aheads – Bohemian Nov 16 '12 at 05:52
1

What does (?= ... ) mean? – gosukiwi May 30 '15 at 21:54
@gosukiwi It is regex syntax for [look-ahead](http://www.regular-expressions.info/lookaround.html) – kev May 31 '15 at 01:07

score 1 · Answer 2 · answered Dec 04 '12 at 21:52

Don't do it all in one regex. Regexes are not a magic toolbox from which all solutions must come.

Check for three different conditions rather than cramming them all into one regex. In Perl this would be:

$ok = ( $s =~ /^[a-zA-Z0-9]{8}$/ && $s =~ /[a-z]/ && $s =~ /[A-Z]/ && $s =~ /[0-9]/ );

It is far clearer what your intent is.

2 Answers2