RegEx - Require minimum length of one group

Question

I'm trying to make a nickname validator. Here are the rules I want:

Total character count must be between 3 and 15

There can be two non-consecutive spaces

Only letters (a-z) are allowed

Each word separated by a space can begin with an uppercase letter, the rest of the word must be lowercase

At least one of the words must have 3 or more characters

This is what I currently have which checks the four first rules, but I have no idea how to check the last rule.

^(?=.{3,15}$)(\b[A-Z]?[a-z]* ?\b){1,3}$

Should match:

Yaw
yaw
James Bond
Monkey D Luffy
List item

Shouldn't match:

YaW
Two spaces (with two consecutive space characters)
No no no
JamesBond

Because it has two spaces between "Two" and "spaces" (a fact that doesn't show up with this formatting) — L. Scott Johnson, Jul 23 '18 at 16:07
Thanks @L.ScottJohnson, I realized it after adding the comment :) — Matt.G, Jul 23 '18 at 16:09
Yeah, I've edited the question to format it so it shows up (and with a comment so it can't be missed). — L. Scott Johnson, Jul 23 '18 at 16:10

score 2 · Accepted Answer · edited Jul 23 '18 at 17:33

2

Try Regex: ^(?=[A-Za-z ]{3,15}$)(?=[A-Za-z ]*[A-Za-z]{3})(?:\b[A-Z]?[a-z]*\ ?\b){1,3}$

Demo

For the last rule, a positive lookahead without space was used (?=[A-Za-z ]*[A-Za-z]{3})

edited Jul 23 '18 at 17:33

YaW

12,012
3
17
21

answered Jul 23 '18 at 16:06

Matt.G

3,363
2
7
21

That's really great. Why have you split the words check in two? One with the space and another one without it? I've tried deleting the last group and changing {1,2} to {1,3} and aparently it's the same because the \b wouldn't allow you to end with a space. – YaW Jul 23 '18 at 17:01
@YaW, you are right, that is not necessary. feel free to edit the answer that worked for you. – Matt.G Jul 23 '18 at 17:07

score 0 · Answer 2 · answered Jul 23 '18 at 20:27

but I have no idea how to check the last rule

As you only allow [A-Za-z] and space in your regex, you could simply use (?=.*?\S{3}) which looks ahead for 3 non white-space characters. .*? matches lazily any amount of any characters.

As soon as 3 non white-space characters are required the initial lookahead can be improved to the negative ^(?!.{16}) as the minimum of 3 is already required in \S{3} ⇒ [A-Za-z][a-z]*

Further you can drop the initial \b which is redundant as there can only be start or space before.

^(?!.{16})(?=.*?\S{3})(?:[A-Za-z][a-z]* ?\b){1,3}$

Here is a demo at regex101 (for more regex info see the SO regex faq)

If your tool supports atomic groups, improve performance by use of (?> instead of (?:

RegEx - Require minimum length of one group

2 Answers2