I want a user to enter their username and have it be 5-8 characters long which would look like this right?



But, I also want the characters to be alpha only, which would be like this:



But when I add the two expressions together, and I enter a username like nathan5, it doesn't flag it as an error.

What expression would I use if not the two above? Or how do I combine the two?




This post has been edited by kkgaming: 4 Feb, 2008 - 07:42 PM

try [a-zA-Z]{5,8}

Yup, I believe that worked, thanks. I also need a password 6-8 characters, start with letter, at least 1 number. I cam e up with this:



But I am not sure how to have one letter first for the password....

This post has been edited by kkgaming: 4 Feb, 2008 - 08:16 PM

try this

[a-zA-Z]+[0-9]+[a-zA-Z0-9]*

That works, but how do I get it to be 5-8 characters only....

well I'm not sure about this but:

([a-zA-Z]+[0-9]+[a-zA-Z0-9]*){5,8}

But as I said, I'm not sure.

hmmm, yeah, that flags a lot of stuff wrong that shouldn't be. I am not sure either...

OK just another thought

([a-zA-Z]\w{3,6}\d)|([a-zA-Z]\d\w{3,6})

yup, that works, but I meant 6,8 not 5,8. Sorry for telling you wrong that does work though. What would it be for 6,8? sorry told you wrong.

I think it would be: (judging by what you did)



However, when I start the password with a letter and have a number in the middle of letters it flags it as an error...It works otherwise..


thanks again, for the help.

This post has been edited by kkgaming: 4 Feb, 2008 - 10:27 PM

Yes, I believe that is correct, but try all the variants that you can think of, it's just a simple finite state automaton

But some how I still have doubts, anyways at least you get the idea.

This post has been edited by PennyBoki: 4 Feb, 2008 - 10:19 PM

Yeah, actually I think it doesn't work quite right. When I have a number within letters it flags it as an error. hmm, it works other than that though. I will try to figure it out, not unless you have another idea.

Perhaps you can try this


Let's look at this part

This looks for an alphanumeric sequence of characters length 6 to 8. Carat ^ to match the start, dollar sign to match the end.

Then it's placed in (?= ... ) for a lookahead match. It'll take more to explain it. Just go with it...

Then you have [a-zA-Z] to match your condition of "must start with alphabet". The next part might be a little complicated to explain. Let's go with the 2 extreme examples first:
"a1bcdefg" and "abcdefg1", representing alpha-numeral-rest_are_alphanumeric and alpha-rest_are_alphanumeric-numeral.

\d matches 1 numeral (so you'll have at least one number somewhere)

You need a starting alphabet, and at least one numeral. That leaves at most 6 more characters, hence the {0,6} part.

So, the first part, the lookahead fulfills your length requirement (between 6 and 8 characters). The second part fulfills your "start with alpha, and at least 1 numeral" requirement. Combine them and you have done it!

For more information, check this regex lookahead article.

FYI, \w matches alphabets, numerals and the underscore character, so it might not be what you want.

Hope this helps!