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

This solution is probably outdated. See the higher voted answer instead; I no longer actively use Xcode and am not qualified to vet a solution.

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Use "External Target":

1. Select "Project" > "New Target..." from the menu
2. Select "Mac OS X" > "Other" > "External Target" and add it to your project
3. Open its settings and fill in your script setup
4. Open the "General" tab of the main target's settings and add the new target as it's direct dependency

Now the new "External Target" runs before the main target even starts gathering dependency information, so that any changes made during the script execution should be included in the build.