Xcodebuild PLATFORM_NAME always == iphoneos

Question

I am trying to create an Xcode project from the command line using iphonesimulator as an SDK. Here is the command line:

xcodebuild -scheme SchemeName -configuration Debug -sdk iphonesimulator PLATFORM_NAME=iphonesimulator clean build 

However, when I add a post-build action to Xcode, for example:

 echo "PLATFORM_NAME: ${PLATFORM_NAME}" 

it always outputs "PLATFORM_NAME: iphoneos ", not iphonesimulator.

Is this a bug, or is there something wrong with my build configuration? Thanks