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# ping-ip-by-pipe.sh
thread=5
tmp_fifo=/tmp/$$.fifo
start_time=$(date +%s)
mkfifo $tmp_fifo
exec {tmp_fd}<> $tmp_fifo #关联一个临时fd到管道
rm -rf $tmp_fifo

for i in $(seq $thread)
do
  echo $i >&${tmp_fd} #放入限定数量的空行
done

for i in {1..30}
do
  read -u ${tmp_fd} #拿走一行，进入下一步，如果无内容会等待
  {
    sleep 1
    ip=192.168.5.$i
    ping -c1 -W1 $ip &>/dev/null
    if [ $? -eq 0 ];then
      echo "$ip is up."
    else
      echo "$ip is down."
    fi
    echo >&${tmp_fd}  #放入一行
  }&
done

wait

stop_time=$(date +%s)
echo "TIME:  $(($stop_time-$start_time))"
exec {tmp_fd}<&-
exec {tmp_fd}>&-

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exec {tmp_fd}<&-
exec {tmp_fd}>&-