Answer by trojanfoe for Xcode - How to run script just before build starts

The best approach is to create pseudo target in your project.

For example, say you have a shell script that sets the app version by updating an .xcconfig file:

• Create a target called SetAppVersion of type Other> External Build System.
• Leave the Build Tool at /bin/bash, set the Arguments to whatever script does the work, for example scripts/set_app_version.sh and set the Directory to $(PROJECT_DIR).

Now for any target affected by this script, simply make the SetAppVersion target a dependency of it, and it will run before any other action is performed on those targets.