linux for 循环

ping.sh

#!/bin/bash
for i in {1..193}
do
  ( ping -c1 -i0.2 -w1 172.16.30.$i &>/dev/null
  if (( $?==0 ))
  then
      echo "172.16.30.$i up"  >>2.txt
  else
      echo "172.16.30.$i down"  >>3.txt
  fi )&  --》这样就把这一段放到后台去执行了，大大加快了速度。
done
sleep 2
live_pc_num=`cat 2.txt|wc -l`
down_pc_num=`cat 3.txt|wc -l`
echo "there are $down_pc_num is down"
echo "there are $live_pc_num is up"
echo "list:"
cat 2.txt
rm -rf 2.txt 3.txt

break 停止循环

#!/bin/bash
i=1
while :
do
    echo "$i"
    (( i++ ))
    if ((  i==20000 )) --》输出的只有1-19999
    then
        break
    fi
done