linux shell变量while循环内改变无法传递到循环外教程

代码示例如下图所示，在while中变量namelist、image\_hash无法传到循环外部。
原因：使用了管道的缘故，当启用管道时，会生成一个subshell，while循环的代码在subshell中执行

function generate_ota_package()
{
    local namelist=$filelist" "$ota_hash_sig

    openssl sha -sha256 $filelist | awk '{print $2}' | head -c 64 > $filelist_hash

    reinit_file $filelist_hash

    cat $filelist | while read line
    do
        partition_name=`echo $line | awk '{print $1}'`
        image=`echo $line | awk '{print $2}'`

        if [[ $image == "" ]];then
            continue
        fi

        namelist=$namelist" "$image
        echo "============"$namelist
        image_hash=`openssl sha -sha256 $image | awk '{print $2}'`
        echo $partition_name" "$image" "$image_hash >> $filelist_hash
    done < $filelist

    echo $namelist
    echo $image_hash

    signature_ota

    tar cvzf $ota_name $namelist
}

修改方案如下：

function generate_ota_package()
{
    local namelist=$filelist" "$ota_hash_sig

    openssl sha -sha256 $filelist | awk '{print $2}' | head -c 64 > $filelist_hash

    reinit_file $filelist_hash

    while read line
    do
        partition_name=`echo $line | awk '{print $1}'`
        image=`echo $line | awk '{print $2}'`

        if [[ $image == "" ]];then
            continue
        fi

        namelist=$namelist" "$image
        echo "============"$namelist
        image_hash=`openssl sha -sha256 $image | awk '{print $2}'`
        echo $partition_name" "$image" "$image_hash >> $filelist_hash
    done < $filelist
    
    echo $namelist
    echo $image_hash

    signature_ota

    tar cvzf $ota_name $namelist
}