[RESOLVED] Regular expressions - Username

I already have a function to check for a valid e-mail address using regular expressions, but I had written it awhile ago when I was still familiar with them.

Now I need one to check for a valid username. The username can only have letters, numbers, underscores (_), spaces, and a single period.

It has to start with a letter. It cannot have consecutive spaces (2 or more in a row).

Can someone help me? :(

Something like

[a-zA-Z]([a-zA-Z0-9_]|( [a-zA-Z0-9_]))*(\.([a-zA-Z0-9_]|( [a-zA-Z0-9_]))*)?

In words: with a name character being an alphanumeric character or an underscore, a username is
an alphabetic character followed by
either a name character, or a space and a name character, repeated any number of times
followed optionally by
a dot and
either a name character, or a space and a name character, repeated any number of times

If you don't want to allow the dot as the last character, replace the last * by a +.
If you don't want to allow the dot as the last character and don't want a space to follow the dot, insert a name character collection after the dot, unconditionally.
As it is, the space character cannot be the last character, nor can it be directly before the dot.

I hope you realise that properly validating email addresses using regular expressions is fairly abstruse. Simple validation is fine, but you invariably cut out 1% of potential addresses.

Quote:

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Originally Posted by CornedBee

Something like

[a-zA-Z]([a-zA-Z0-9_]|( [a-zA-Z0-9_]))*(\.([a-zA-Z0-9_]|( [a-zA-Z0-9_]))*)?

In words: with a name character being an alphanumeric character or an underscore, a username is
an alphabetic character followed by
either a name character, or a space and a name character, repeated any number of times
followed optionally by
a dot and
either a name character, or a space and a name character, repeated any number of times

If you don't want to allow the dot as the last character, replace the last * by a +.
If you don't want to allow the dot as the last character and don't want a space to follow the dot, insert a name character collection after the dot, unconditionally.
As it is, the space character cannot be the last character, nor can it be directly before the dot.

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Wow thanks, that looks promising. I'll give it a try and report back. :)

Quote:

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Originally Posted by penagate

I hope you realise that properly validating email addresses using regular expressions is fairly abstruse. Simple validation is fine, but you invariably cut out 1% of potential addresses.

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Wow. I'm not sure how well that would perform in PHP. Especially under high traffic. Shouldn't be too much of a problem, though. If they really want to register they'll use a different e-mail address. Thanks.

cornedbee: wow this is good. can you pls modify it to not include white space characters? thanks, greatly appreciate it

or is this correct
[a-zA-Z]([a-zA-Z0-9_]|([a-zA-Z0-9_]))*(\\.([a-zA-Z0-9_]|([a-zA-Z0-9_]))*)?