Managing shaders for different models with different textures

I have a scene-manager which loads models from different files. Some models have textures like normal-map and specular-map some don't have one of which and some just have a diffuse (color) texture. As far as I noticed I need to generate different shader-programs to support all possible combinations. well I can do that but the problem is that when I want to to make a simple change in a shader's code (for example fragment-shader) I need to update all sources. So, I was wondering that  is there any better solution for this? Or I need to write a …