macOS Xcode custom build rule advice

You are asking how to do two things that seem slightly different in concept but have remarkably different approaches in practice.

First things first: you know the file you want to work with. Add a custom script build phase to your target. Two very important details are that you need to specify the input files and the output files. Using environment variables should be very helpful. I wanted to run flex on a file, but I didn't like the default arguments Xcode passes, so I created my own script.

$(SRCROOT) is in your project settings. It's the root folder of your project, configured to be relative to your xcode project. $(DERIVED_FILE_DIR) is in your Build directory. You don't *have* to used this to specify the location of output. You can put it anywhere. Just make sure that you specify input files and output files at the bottom of the window. If you don't, dependencies won't work, so it won't rerun the script when files change. Also, if you're using these environment variables, it's important to note that the method used to reference them varies. See the attached screenshot.


The generic approach is something I have not done. It's configured under the "Rules" tab of the Target settings.