Regular Expression for alphanumeric and underscores

Question

I would like to have a regular expression that checks if a string contains only upper and lowercase letters, numbers, and underscores.

Answer 1

Try these multi-lingual extensions I have made for string.

IsAlphaNumeric - String must contain atleast 1 alpha (letter in Unicode range, specified in charSet) and atleast 1 number (specified in numSet). Also, the string should comprise only of alpha and numbers.

IsAlpha - String should contain atleast 1 alpha (in the language charSet specified) and comprise only of alpha.

IsNumeric - String should contain atleast 1 number (in the language numSet specified) and comprise only of numbers.

The charSet/numSet range for the desired language can be specified. The Unicode ranges are available on below link:

http://www.ssec.wisc.edu/~tomw/java/unicode.html

API :

    public static bool IsAlphaNumeric(this string stringToTest)
    {
        //English
        const string charSet = "a-zA-Z";
        const string numSet = @"0-9";

        //Greek
        //const string charSet = @"\u0388-\u03EF";            
        //const string numSet = @"0-9";

        //Bengali
        //const string charSet = @"\u0985-\u09E3";
        //const string numSet = @"\u09E6-\u09EF";

        //Hindi
        //const string charSet = @"\u0905-\u0963";
        //const string numSet = @"\u0966-\u096F";

        return Regex.Match(stringToTest, @"^(?=[" + numSet + @"]*?[" + charSet + @"]+)(?=[" + charSet + @"]*?[" + numSet + @"]+)[" + charSet + numSet +@"]+$").Success;
    }

    public static bool IsNumeric(this string stringToTest)
    {
        //English
        const string numSet = @"0-9";

        //Hindi
        //const string numSet = @"\u0966-\u096F";

        return Regex.Match(stringToTest, @"^[" + numSet + @"]+$").Success;
    }

    public static bool IsAlpha(this string stringToTest)
    {
        //English
        const string charSet = "a-zA-Z";

        return Regex.Match(stringToTest, @"^[" + charSet + @"]+$").Success;
    }

Usage :

        //English
        string test = "AASD121asf";

        //Greek
        //string test = "Ϡϛβ123";

        //Bengali
        //string test = "শর৩৮";

        //Hindi
        //string test = @"क़लम३७ख़";

        bool isAlphaNum = test.IsAlphaNumeric();