真的坑爹，今天才开始玩MAC OX，装了个最新版本的10.7.3，只能装XCODE 4.3 这个月刚发行的版本。
安装时发现没有install过程，直接双击就进入开发环境了。而且装完后没有gcc 等各种编译工具，在TERMINAL下各种命令不识别，想装ruby的各种开发工具，都不行了。

查了半天才发现：
Apple announced Xcode 4.3 for OSX Lion and 4.4 for OSX Mountain Lion last week. The major difference is that Xcode no longer provide an installer which is good thing because you now could update Xcode with AppStore in the future, plus it is much easier to carry the development environment with you. However, there is a little problem with this new version of Xcode, is that all command line toolsets and compilers are not visible in terminal.

解决方案一：
A simple fix is to update your PATH env:
export PATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:$PATH
Please be noted that clang does not reside in /Developer/usr/bin, it is now in /Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
Now you could access to gcc, g++, git or any toolsets bundled with Xcode. For your convenience, it is recommended to include it in your .bash_profile.
解决方案二：
You can install these additional tools directly in Xcode :
Preferences > Downloads > Command Line Tools > Install