android系统开发每次编译系统都要先执行envsetup.sh文件，这是为什么，
- 今天我们从
build/envsetup.sh文件的开头位置找到了原因
- 原因就是执行
. build/envsetup.sh这个脚本就会临时添加下面的shell函数到我们的环境变量，后续使用的lunch、make、m、mm等命令才有效
- 除了常用的lunch、make、m命令之外，其他的命令也可以从这里找到并熟悉它们，不用每次都到处百度搜索了
Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment:
- lunch: lunch <product_name>-<build_variant>
Selects <product_name> as the product to build, and <build_variant> as the variant to
build, and stores those selections in the environment to be read by subsequent
invocations of 'm' etc.
- tapas: tapas [<App1> <App2> ...] [arm|x86|mips|arm64|x86_64|mips64] [eng|userdebug|user]
- croot: Changes directory to the top of the tree, or a subdirectory thereof.
- m: Makes from the top of the tree.
- mm: Builds all of the modules in the current directory, but not their dependencies.
- mmm: Builds all of the modules in the supplied directories, but not their dependencies.
To limit the modules being built use the syntax: mmm dir/:target1,target2.
- mma: Builds all of the modules in the current directory, and their dependencies.
- mmma: Builds all of the modules in the supplied directories, and their dependencies.
- provision: Flash device with all required partitions. Options will be passed on to fastboot.
- cgrep: Greps on all local C/C++ files.
- ggrep: Greps on all local Gradle files.
- jgrep: Greps on all local Java files.
- resgrep: Greps on all local res/*.xml files.
- mangrep: Greps on all local AndroidManifest.xml files.
- mgrep: Greps on all local Makefiles files.
- sepgrep: Greps on all local sepolicy files.
- sgrep: Greps on all local source files.
- godir: Go to the directory containing a file.
- allmod: List all modules.
- gomod: Go to the directory containing a module.
- pathmod: Get the directory containing a module.
- refreshmod: Refresh list of modules for allmod/gomod.
1. source ./build/envsetup.sh
2. m help
