J. mp wrote:
> Vincent Fourmond wrote:
>   
>> 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
>>>       
>>   Just to get you started:
>>
>>   /[a-z]+(\.[a-z]+)?/
>>
>>   Vince
>>     
>
>
> First of all, thanks for the attention.
> More details:
>
> max size allowed is 30
> min size allowed is 5
>
> the follwoing chars are allowed :
> - _ . (Slash, undescore, perdiod)
>
> these chars are not allowed as start neither as ending char
>
> any alphabetic char, english chars only
> case insensitive
> no numbers
>
> eg
> .username ->invalid
> user-name -> valid
> _username -> invalid
> user.name -> valid
> user_name ->valid
>
>   

/\A[[:alpha:]][-_.[:alpha:]]{3,28}[[:alpha:]]\z/

> basically I want allow the same pattern allowed for emails but before 
> the @ char :)
>
>   
The above regexp does not do this. Certainly you can have numbers in 
your email address, for example. Basically anything is allowed before 
the @. Google "regular expression email address" for extensive 
discussions about this.