Regular Expression for User Name

Question

Hi,

Do any one of you know the regular expression for user name that allows special characters(. and _) but not at the end of the string. For example, it should not allow the user to enter "john123." or "John_". But the otherwise is acceptable. For example, the user names "john.harlow" or "john_harlow".

Thanks
Shwetha

shwetha sonar · Answer

Hey, Thanks for the reply. The suggested regular expression does not work. It still does not meet the requirements. Shwetha

Vulpes · Answer

It struck me subsequently that, if the user name can contain any characters, then it's no longer necessary to use 'lookahead'. I used it before when I thought that the names would probably be limited to alphanumerics or your special characters. You could therefore simplify the regular expression to: string regexp = @".*[^_\.]$";

Vulpes · Answer

If you don't want . or _ to appear last but, otherwise, the user name can contain absolutely anything including those characters, then you can use this: string regexp = @"(?=.*[^_\.]$)";

shwetha sonar · Answer

Hi, Thanks for the reply. But, the suggested expression does not meet the requirement. It is not allowing me to enter the special characters I want (ie . and _). Also, majorly it does not accept any string for the user name. For example: only aplhabets or aplhanumeric. Regards Shwetha

Vulpes · Answer

Try this: string regexp = @"^(?=.*[^_\.]+$)[A-Za-z0-9_\.]+$";