Question

I want to define a ‘valid’ input, which is _-. won’t be allowed in the end or in the begining of the string, only allowed in the middle.

Acceptable characters (location doesn’t matter): a-zA-Z0-9 and all the hebrew letters which I don’t know how to allow them in a regex (maybe just hard-coding all the letters?)

Unacceptable characters (location doesn’t matter): All symbols, except the special ones I provided before.

I don’t know how to build this pattern, and if you can add tips and comments on every section so I will understand. Thanks!

This is not for homework, just for self learning.

Answer 1

@"^[a-zA-Z\dא-ת][a-zA-Z_\-\.\dא-ת]*[a-zA-Z\dא-ת]$"

If you want to allow “_.-” without duplicates:

@"^[a-zA-Z\dא-ת]([a-zA-Z\dא-ת]+[_\.\-]?)*[a-zA-Z\dא-ת]$"

If you want to allow white spaces in the middle:

@"^[a-zA-Z\dא-ת][a-zA-Z_\-\.\d\sא-ת]*[a-zA-Z\dא-ת]$"

If you want white spaces + “_.-” without duplicates:

@"^[a-zA-Z\dא-ת]([a-zA-Z\d\sא-ת]+[_\.\-]?)*[a-zA-Z\dא-ת]$"

So using the Regex:

var isValid = Regex.IsMatch(input, @"...");

Also, if you plan on using the regex many times in the code, I suggest adding RegexOptions.Compiled flag, to increase speed.

var isValid = Regex.IsMatch(input, @"...", RegexOptions.Compiled);