Xcode: Running a script before every build that modifies source code directly

Question

What I did:

I have a script that

1. Read some configuration files to generate source code snippets
2. Find relevant Objective-C source files and

Answer 1

Every technique mentioned so far is an overkill. Reproducing steve kim's comment for visibility:

In the build phases tab, simply drag the "Run Script" step to a higher location (e.g. before "Compile Sources").

Tested on XCode 6