xcodebuild: simulator or device?

An Xcode build from the command line looks like:

xcodebuild -configuration ${BUILD_TYPE} -target ${TARGET_NAME} -arch ${CPU_ARCHITECTURE} -sdk ${SIMULATOR_OR_IOS_SDK} 

BUILD_TYPE is something like "Release" or "Debug" (those are the defaults, you may have added others to the project)

TARGET_NAME is the name of the target you are building (by default the same name as your project)

CPU_ARCHITECTURE is the CPU you are building for, one of:

i386, armv6, armv7

Use i386 for simulator builds, and use either armv6 or armv7 for device builds - note that some other devices cannot run armv7 code, so usually when building libraries it's a good idea to build all of these architectures and then glue them together using lipo.

SIMULATOR_OR_IOS_SDK is what you are looking for, it's either iphoneos or iphonesimulator. Those values use the latest version of the SDK that the installed Xcode supports, you can get a list of supported SDK's with:

xcodebuild -showsdks

Which returns a list like:

Mac OS X SDKs:
    Current Mac OS                  -sdk 
    Mac OS X 10.6                   -sdk macosx10.6

iOS SDKs:
    iOS 4.2                         -sdk iphoneos4.2

iOS Simulator SDKs:
    Simulator - iOS 3.2             -sdk iphonesimulator3.2
    Simulator - iOS 4.0             -sdk iphonesimulator4.0
    Simulator - iOS 4.1             -sdk iphonesimulator4.1
    Simulator - iOS 4.2             -sdk iphonesimulator4.2

xcodebuild has more flags than that, but those are the ones you'd commonly use after using Xcode to set up the build properties. You don't have to use all of them, but it's probably a good idea to be clear about what you are building - otherwise I believe your last settings are used.

i find the -xcconfig flag quite useful. this option allows you to specify a path to an xcconfig (build settings file). within an xcconfig, you may #include other xcconfig files.