參考連結： 

https://bg2bkk.github.io/post/shell%E5%A4%9A%E7%BA%BF%E7%A8%8B%E5%AE%9E%E8%B7%B5/

$cat steps.sh
rm -r output
mkdir -p output

#允許的程序數
THREAD_MAX=24

#$$是程序pid
Pfifo="/tmp/$$.fifo"
mkfifo $Pfifo

#定義描述符為8848的管道
exec 8848<>$Pfifo
rm -f $Pfifo

#預先寫入指定數量的換行符，一個換行符代表一個程序
for ((i=0;i<$THREAD_MAX;i++))
do
    echo -ne "\n" 1>&8848
done

for URL in `cat CVE_XML_urls`; do
{

        CVE_in_XML=`basename $URL|sed -e "s/.gz$//g"`;
        wget $URL;
        gunzip -f $CVE_in_XML.gz

        echo $CVE_in_XML;

        perl convert-nvdcve $CVE_in_XML

        grep cpe $CVE_in_XML|grep product |sort|awk -F '<|>' '{ if($3!="") print $3 }' > $CVE_in_XML.cpe

        for cpe_entry in `cat $CVE_in_XML.cpe`; do
        {
                #程序控制
                read -u 8848
                {

                        echo $cpe_entry;
                        vendor=`echo $cpe_entry |awk -F ":" '{print $3}'`
                        product=`echo $cpe_entry |awk -F ":" '{print $4}'`
                        perl NVD_parser.pl $CVE_in_XML.db $CVE_in_XML.idx_cpe.db $cpe_entry >> output/$vendor.$product.urls;
                        echo -ne "\n" 1>&8848
                }&
        }
        done
}&
done

wait

#關閉管道
exec 8848>&-

echo "\nDone"