Building with Xcode command line tools

To build an app with Xcode command line tools xcrun xcodebuild should be used. Here is an example on how to build Food Truck app for iOS simulator target:
xcrun xcodebuild -scheme 'Food Truck' \
-project 'Food Truck.xcodeproj' \
-configuration Debug \
-sdk 'iphonesimulator' \
-destination 'generic/platform=iOS Simulator' \
-derivedDataPath \
The .app file can be then found under /build folder, which can be modified via the last parameter of the script.

Building with Fastlane

If you use fastlane for your automation pipelines the script should look the following way:
configuration: build_config[:configuration],
scheme: build_config[:scheme],
workspace: build_config[:xcode_workspace],
xcargs: "-quiet -sdk 'iphonesimulator' -destination 'generic/platform=iOS Simulator'",
derivedDataPath: IOS_DERIVED_DATA_PATH # this will contain the .app which we need later on