IMHO, better approach is to set version string from git tag and build number from git commit count in master
What about using Apple's Generic Versioning System? They even provide you with avgtool.
There's also fastlane with some commands that use avgtool to bump your build and version numbers.
If you are using VCS then you need to save your bump each time, producing this infinite "Bump version" commits. They look not very nice in VCS log