function lunch()
{
    //执行Uitype函数，在这里面是选择letv的UITYPE，这个是自己定义的。
    uitype
    if [ $? -ne 0 ];then
        echo "** Invalid uitype!!!"
        return 1
    fi
    //定义answer局部变量，用来存储选择的项
    local answer
    //如果带参数，比如lunch U4-eng-32，就直接把这个参数存在answer，如果不带参数，就通过用户自己选择
    if [ "$1" ] ; then
        answer=$1
    else
        print_lunch_menu
        echo -n "Which would you like? [aosp_arm-eng] "
        read answer
    fi
    local selection=
    //根据用户选择，通过LUNCH_MENU_CHOICES数组找到对应的项，赋值给answer.最后赋值给selection
    if [ -z "$answer" ]
    then
        selection=aosp_arm-eng
    elif (echo -n $answer | grep -q -e "^[0-9][0-9]*$")
    then
        if [ $answer -le ${#LUNCH_MENU_CHOICES[@]} ]
        then
            selection=${LUNCH_MENU_CHOICES[$(($answer-1))]}
        fi
    elif (echo -n $answer | grep -q -e "^[^-][^-]*-[^-][^-]*$")
    then
        selection=$answer
    elif (echo -n $answer | grep -q -e "^[^-][^-]*-[^-][^-]*-[^-][^-]*$")
    then
        selection=$answer
    fi
    if [ -z "$selection" ]
    then
        echo
        echo "Invalid lunch combo: $answer"
        return 1
    fi
    //分析select变量，分享出product和variant，比如U4-user-32,product是U4，variant是eng。
    export TARGET_BUILD_APPS=
    local product=$(echo -n $selection | sed -e "s/-.*$//")
    check_product $product
    if [ $? -ne 0 ]
    then
        echo
        echo "** Don't have a product spec for: '$product'"
        echo "** Do you have the right repo manifest?"
        product=
    fi
    local variant=$(echo -n $selection | sed -e "s/^[^-]*-//" | sed -e "s/-.*$//")
    check_variant $variant
    if [ $? -ne 0 ]
    then
        echo
        echo "** Invalid variant: '$variant'"
        echo "** Must be one of ${VARIANT_CHOICES[@]}"
        variant=
    fi
    local android_build_type=$(echo -n $selection | sed -e "s/$product-$variant//" | sed -e"s/-//")
    if [ -z "$product" -o -z "$variant" ]
    then
        echo
        return 1
    fi
//    把变量导出
    export TARGET_PRODUCT=$product
    export TARGET_BUILD_VARIANT=$variant
    export TARGET_BUILD_TYPE=release
    if [ -n "$android_build_type" ]
    then
        echo "ANDROID_BUILD_TYPE=$android_build_type"
        export ANDROID_BUILD_TYPE=$android_build_type
    fi
    echo
//通过set_stuff_for_environment来设置一些值，等会看。
    set_stuff_for_environment
//打印出配置之后的项
    printconfig                                                                                                                                                                              
}

在最开始时候，会调用uitype，即把你选择的UITYPE类型赋值给变量LETV_UI_TYPE，这个变量在各个模块都有调用，用于选择编译。

来看set_stuff_for_environment函数，这里面有设置JAVA_HOME, title等一些操作

function set_stuff_for_environment()
{
    settitle
    set_java_home
    setpaths
    set_sequence_number                                                                                                                                                                      
    export ANDROID_BUILD_TOP=$(gettop)
    # With this environment variable new GCC can apply colors to warnings/errors
    export GCC_COLORS='error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01'
    export ASAN_OPTIONS=detect_leaks=0
}

settitle会设置当面终端的的显示，如下：

 set_java_home