Build and run an app on simulator using xcodebuild
Ok. Figured out the issue.
You need to specify the correct destination. For example.
xcrun xcodebuild \ -scheme $XCODE_SCHEME \ -project $XCODE_PROJECT \ -configuration Debug \ -destination 'platform=iOS Simulator,name=iPhone 6 Plus,OS=9.1' \ -derivedDataPath \ buildIn this way Xcode will create the folder (called build) containing your products (in particular look at Debug-iphonesimulator). The build dir is created within the dir you are running the xcodebuild command.
Now you can point that folder in order to run the ios-sim command (see ios-sim for more references) or simctl (see iOS 8: Building custom simulators and Build And Run iOS Apps In Commmand Line for more info).