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Finding special characters in a username

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Aug 22.2009

I’m writing a script to validate a username for a registration page. I want to alert the user if they have any special characters in their username, and I am using the php preg_match() function to test for special characters. I’m not very good with regular expressions, does anyone know a good regular expression to match all special characters wherever they may be in the username string? Also is there a better way to do this than using preg_match?

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@MindzaiAug 22.2009 — It is easier and more efficient to validate against an allowed set of characters rather than trying to exclude everything individually. For example, if you only want to allow letters, numbers and underscores:

[code=php]$valid = preg_match('/[a-z0-9_]+/i', $username);[/code]
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@adamscott421authorAug 22.2009 — Thanks for the tip that really helped. What do the forward slashes and the 'i' mean in the example regex you gave?
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