(1) mac基础路径
~=当前账户的HOME目录，例如“/Users/xxx”
(2) Xcode中的路径
build默认路径：BUILD_PATH = ~/Library/Developer/Xcode/DerivedData/xxx-xxx-xxxxxxx/Build
可通过“File->Project Settings”查看Derived Data Location。
环境变量宏（Build Setting Macros）引用格式：${MACRO}，同Build Phases Run Script中的语法。
(a) ARCH & PLATFORM & SDK
ARCHS = i386
CURRENT_ARCH = i386
PLATFORM_DIR = /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform
PLATFORM_NAME = macosx
SDKROOT = /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk
SDK_DIR = /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk
SDK_NAME = macosx10.9
(b) PROJECT & SOURCE
PROJECT = HelloWorld
PROJECT_DIR =~/Projects/Learn Objective-C/HelloWorld
PROJECT_FILE_PATH =${PROJECT_DIR}/HelloWorld.xcodeproj
PROJECT_NAME = HelloWorld
SOURCE_ROOT =${PROJECT_DIR}
SRCROOT =${PROJECT_DIR}
(c) BUILD & CONFIGURATION
BUILD_DIR =
${BUILD_PATH}/Products
BUILD_ROOT =${BUILD_PATH}/Products
BUILT_PRODUCTS_DIR ={BUILD_PATH}/Products/Debug
CONFIGURATION = Debug
CONFIGURATION_BUILD_DIR =${BUILD_PATH}/Products/Debug
CONFIGURATION_TEMP_DIR =${BUILD_PATH}/Intermediates/HelloWorld.build/Debug
(d) PRODUCT & TARGET
PRODUCT_NAME = HelloWorld
PRODUCT_TYPE = com.apple.product-type.tool//Project Template: Command Line Tool
TARGET_BUILD_DIR =${BUILD_PATH}/Products/Debug
TARGET_NAME = HelloWorld
(3) 设置环境变量
Product -> Edit Scheme（option+command+R）->Arguments->Environment Variables中可以添加自定义环境变量（Name为名称，Value为值）。
