regular expression like SQL [closed] - asp.net

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I have a search field form that I use to insert filterexpression on a aspx page.
I would like to force user to insert a string similar to a sql like condition, so it can be:
Start or not with %, so %?
Write letters, numbers, whitespace, underscore but not a special character like %, so [A-Za-z0-9-_+()\s]+
Ends or not with %, so %?$
My reg expression is %?[A-Za-z0-9-_+()\s]+%?$ but it doesn't work because I can write %test%test% that is not a sql like condition.
I have to force writing %test or test% or test or %test% but not %test%test% because the search goes in an error page.
How to do this?
Thanks

Answer 1

You were very close, just missing the start of string operator ^. Without that, you allow a match on your regex on any part of the input, which is why you were able to match things like %test%test%. The expression as you had it would just match starting at the second %.
using System.Text.RegularExpressions;
using System;
public class Program{
public static void Main(string[] args) {
Regex rgx = new Regex(#"^%?[A-Za-z0-9-_+()\s]+%?$");
Console.WriteLine(rgx.IsMatch("%test%")); //True
Console.WriteLine(rgx.IsMatch("%test %test%")); //False
}
}