Regex pattern for checking if a string starts with a certain substring?

Question

What\'s the regular expression to check if a string starts with \"mailto\" or \"ftp\" or \"joe\" or...

Now I am using C# and code like this in a big if with many ors

Answer 1

For the extension method fans:

public static bool RegexStartsWith(this string str, params string[] patterns)
{
    return patterns.Any(pattern => 
       Regex.Match(str, "^("+pattern+")").Success);
}

Usage

var answer = str.RegexStartsWith("mailto","ftp","joe");
//or
var answer2 = str.RegexStartsWith("mailto|ftp|joe");
//or
bool startsWithWhiteSpace = "  does this start with space or tab?".RegexStartsWith(@"\s");