Regex for Username?

I am using C# and jQuery to valid a username with Regex. Just learning :) So far I have

UserName = "[开发者_如何学Goa-zA-Z0-9]";

But this doesn't stop symbols ? How to ensure that no symbols or " . " or " _ " ?

Thanks

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That regex says "At least one letter or number" you want "Every character from the start to the end is a letter or number"

"^[a-zA-Z0-9]+$"

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you can also add @ , . %^&* digits character in below regex @"^[a-zA-Z0-9._@#$% ]+$"