Apply mask to a string

Question

I am reading a string ID value from a table. When the ID was input by the user, it was done with an input mask that the user defined, so the mask could have been something

Answer 1

This does exactly what I need. The only downside is that it ties me to the Windows Forms assembly.

        MaskedTextBox mtb = new MaskedTextBox("FR999_999999");
        mtb.Text = "123456789";
        return mtb.Text;