A handy reference when writing pre- and post-trigger scripts for Xcode Server bots:

https://developer.apple.com/library/content/documentation/IDEs/Conceptual/xcode_guide-continuous_integration/EnvironmentVariableReference.html

An old article for the previous iteration of Xcode Server, but it’s a good starting point:

https://honzadvorsky.com/articles/2015-05-04-under-the-hood-of-xcode-server/