build/envsetup.sh中hmm、get_abs_build_var、get_build_var解析

 function hmm() {
   # 打印帮助信息
   cat <<EOF
   Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment:
   - lunch:   lunch <product_name>-<build_variant>
   - tapas:   tapas [<App1> <App2> ...] [arm|x86|mips|armv5|arm64|x86_64|mips64] [eng|userdebug|user]
   - croot:   Changes directory to the top of the tree.
   - 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.
  - 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.
  - sgrep:   Greps on all local source files.
  - godir:   Go to the directory containing a file.

  Look at the source to view more functions. The complete list is:
  EOF
  # gettop是脚本内函数，功能:返回当前android代码树的顶层路径。前提是当前路径位于android代码树中
      T=$(gettop)
  # A变量 局部变量化
      local A
      A=""
  # 查看envsetup.sh内容，且行首开始空格、制表符任意次，替换function为匹配的子串（函数名），按字符排升序、去掉重复
      for i in `cat $T/build/envsetup.sh | sed -n "/^[ \t]*function /s/function \([a-z_]*\).*/\/p" | sort | uniq`; do
  # 替换出来的函数名 追加在A后 并打印
        A="$A $i"
      done
      echo $A
  }

//---------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 #得到build变量(脚本内)的绝对路径
 function get_abs_build_var()
 {
     # 得到源码树顶层目录
     T=$(gettop)
     # 源码树顶层目录有效性容错
     if [ ! "$T" ]; then
         echo "Couldn't locate the top of the tree.  Try setting TOP." >&
         return
     fi
     # 进入顶层目录，设置build变量，
     # 通过make指定build/core/config.mk文件
     # --no-print-directory:不要再屏幕上打印"Entering directory..
     # CALLED_FROM_SETUP=true：打印出dumpvar-abs-$1所表示的变量的值必须先设置CALLED_FROM_SETUP
     # BUILD_SYSTEM:设置所有的编译脚本路径
     (\cd $T; CALLED_FROM_SETUP=true BUILD_SYSTEM=build/core \
       command make --no-print-directory -f build/core/config.mk dumpvar-abs-$)
 }

 function get_build_var()
 {
     T=$(gettop)
     if [ ! "$T" ]; then
         echo "Couldn't locate the top of the tree.  Try setting TOP." >&
         return
     fi
     # 注释同上 唯一不同是目标dumpvar-$1不同
     (\cd $T; CALLED_FROM_SETUP=true BUILD_SYSTEM=build/core \
       command make --no-print-directory -f build/core/config.mk dumpvar-$)
 }

题外话：

BUILD_SYSTEM设置的Makefile目录——build/core目录下所有Makefile一览

config.mk详见一篇，此处一笔带过，只为得到CALLED_FROM_SETUP=true BUILD_SYSTEM=build/core command make --no-print-directory -f build/core/config.mk dumpvar-$1”最终执行结果与过程。

..... include $(BUILD_SYSTEM)/dumpvar.mk

继续引入dumpvar.mk

 # MAKECMDGOALS 变量是传进来的目标dumpvar-abs-$1或 dumpvar-$1的abs-$1或$
 dumpvar_goals := \
         $(strip $(patsubst dumpvar-%,%,$(filter dumpvar-%,$(MAKECMDGOALS))))
 ifdef dumpvar_goals

   ifneq ($(words $(dumpvar_goals)),)
     $(error Only one "dumpvar-" goal allowed. Saw "$(MAKECMDGOALS)")
   endif

   # If the goal is of the form "dumpvar-abs-VARNAME", then
   # treat VARNAME as a path and return the absolute path to it.
   absolute_dumpvar := $(strip $(filter abs-%,$(dumpvar_goals)))
 # 是否有abs
   ifdef absolute_dumpvar
     dumpvar_goals := $(patsubst abs-%,%,$(dumpvar_goals))
     ifneq ($(filter /%,$($(dumpvar_goals))),)
       DUMPVAR_VALUE := $($(dumpvar_goals))
     else
       DUMPVAR_VALUE := $(PWD)/$($(dumpvar_goals))
     endif
 # get_abs_build_var()中dumpvar-abs-$1对应的
     dumpvar_target := dumpvar-abs-$(dumpvar_goals)
   else
     DUMPVAR_VALUE := $($(dumpvar_goals))
 # get_build_var()中dumpvar-$1对应的
     dumpvar_target := dumpvar-$(dumpvar_goals)
   endif

 .PHONY: $(dumpvar_target)
 # 执行目标与执行语句
 $(dumpvar_target):
         @echo $(DUMPVAR_VALUE)

即打印

其中如有abs则ifdef absolute_dumpvar->DUMPVAR_VALUE := $(PWD)/$($(dumpvar_goals))，打印信息增加pwd绝对路径

如没有  则else->DUMPVAR_VALUE := $($(dumpvar_goals)),打印信息没有绝对路径

//---------------------------------------------------------------------------------------------------------------------------------------------------------------------------

envsetup.sh使用方法：

book@book-virtual-machine:/work/android-5.0.$ source build/envsetup.sh
including device/asus/deb/vendorsetup.sh
including device/asus/fugu/vendorsetup.sh
including device/asus/tilapia/vendorsetup.sh
including device/asus/flo/vendorsetup.sh
including device/asus/grouper/vendorsetup.sh
including device/samsung/manta/vendorsetup.sh
including device/friendly-arm/tiny4412/vendorsetup.sh
including device/lge/mako/vendorsetup.sh
including device/lge/hammerhead/vendorsetup.sh
including device/moto/shamu/vendorsetup.sh
including device/generic/mini-emulator-mips/vendorsetup.sh
including device/generic/mini-emulator-armv7-a-neon/vendorsetup.sh
including device/generic/mini-emulator-arm64/vendorsetup.sh
including device/generic/mini-emulator-x86/vendorsetup.sh
including device/generic/mini-emulator-x86_64/vendorsetup.sh
including sdk/bash_completion/adb.bash
book@book-virtual-machine:/work/android-5.0.$ get_abs_build_var TARGET_PRODUCT
/work/android-5.0./full