1 seq语句

2 for语句

3 应用-监控某主机存活脚本

for ((;;))
do
        ping -c1 $1 &>/dev/null
        if [ $? -eq 0 ]; then
                echo -e "`date +"%F %H:%M:%S"` $1 is UP"
        else
                echo -e "`date +"%F %H:%M:%S"` $1 is DOWN"
        fi
        # 每5秒ping一次
        sleep 5
done

注:
ping -c1 $1 &>/dev/null

ping -c1: c指count, 这里就是只ping一次
&: 指后台运行

/dev/null: 标准输出和错误输出都输出到空设备上, 其实就是丢弃所有输出

4 应用-输入字符Q时退出
for ((;;))
do
      read -p "char:" ch
      if [ $ch == "Q" ]; then
              break
      else
              echo "你输入的字符是:$ch"
      fi
done
5 应用-跳出多次循环
for((i=0;i<100;i++));do 
      echo "loop$i" 
      for((;;));do 
              echo "directly break 2 layer" 
              break 2 
      done 
done
6 应用-丈母娘选女婿
```shell read -p “money:” money read -p “car:” car read -p “house:” house

while (( $money < 10000 )) || (( $car < 1 )) || (( $house < 1 )); do echo “不行” read -p “money:” money read -p “car:” car read -p “house:” house done

echo “给你了”

<a name="OdoIS"></a>
# 7 应用-九九乘法表
```shell
for((i=1;i<10;i++)); do
        for((j=1;j<=i;j++)); do
                echo -n -e "$i*$j=$(($i*$j))\t"
        done
        echo ""
done