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 \([a-z_]*\).*/\1/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." >&2
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-$1)
}

function get_build_var()
{
T=$(gettop)
if [ ! "$T" ]; then
echo "Couldn't locate the top of the tree.  Try setting TOP." >&2
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-$1)
}

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$1
dumpvar_goals := \
$(strip $(patsubst dumpvar-%,%,$(filter dumpvar-%,$(MAKECMDGOALS))))
ifdef dumpvar_goals

ifneq ($(words $(dumpvar_goals)),1)
$(error Only one "dumpvar-" goal allowed. Saw "$(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-5.0.2$ 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-5.0.2$ get_abs_build_var TARGET_PRODUCT
/work/android-5.0.2/full