C# Regular Expression to match letters, numbers and underscore

Question

I am trying to create a regular expression pattern in C#. The pattern can only allow for:

• letters
• numbers
• underscores

So far I am having little luck (i'm not good at RegEx). Here is what I have tried thus far:

// Create the regular expression
string pattern = @"\w+_";
Regex regex = new Regex(pattern);

// Compare a string against the regular expression
return regex.IsMatch(stringToTest);

Answer 1

EDIT :

@"^[a-zA-Z0-9\_]+$"

or

@"^\w+$"

Answer 2

@"^\w+$"

\w matches any "word character", defined as digits, letters, and underscores. It's Unicode-aware so it'll match letters with umlauts and such (better than trying to roll your own character class like [A-Za-z0-9_] which would only match English letters).

The ^ at the beginning means "match the beginning of the string here", and the $ at the end means "match the end of the string here". Without those, e.g. if you just had @"\w+", then "@@Foo@@" would match, because it contains one or more word characters. With the ^ and $, then "@@Foo@@" would not match (which sounds like what you're looking for), because you don't have beginning-of-string followed by one-or-more-word-characters followed by end-of-string.

Answer 3

Try experimenting with something like http://www.weitz.de/regex-coach/ which lets you develop regex interactively.

It's designed for Perl, but helped me understand how a regex works in practice.

Answer 4

Regex

packedasciiRegex = new Regex(@"^[!#$%&'()*+,-./:;?@[\]^_]*$");