官方定义：
Invoke “. build/envsetup.sh” from your shell to add the following functions to your environment:
– croot: Changes directory to the top of the tree.– godir: Go to the directory containing a file.
即在已经下载好Android源码android目录下面执行：. build/envsetup.sh 或source build/envsetup.sh,即可开始使用上面命令
Android 常用工作命令mmm,mm,m,croot,cgrep,jgrep,resgrep,godir
原文：http://blog.csdn.net/yelangjueqi/article/details/44222855