J. mp wrote:
> Hi folks,
> I'm burning my head because i don't understand how regular expressions
> works
>
> I just want to validade a username wher
> username ->valid
> user.name ->valid
>
> everything else is invalid
>
> let me know the reg exp to do this
>
>   
I think more details are necessary. What characters are allowed in 
"username"? Just alphabetic? Alphabetic+numbers? Anything else? Is there 
a minimum number of characters? A maximum? Just Latin characters? 
Similarly for "user.name" Is it the same as "username" except with a 
period? Does there have to be exactly four characters before the period 
and four after it? Any other constraints?

To use regular expressions you must be able to precisely state what a 
"match" means.