④.shell 循环语句for

示例：

for i in  1 2 3
do
   echo $i
done

#!/bin/bash
for i in  {1..100}
do
   echo $i
done

for 循环指定分隔符

以冒号为分隔符       IFS=:
以换行符作为分隔符   IFS=$'
'   以行为单位读取数据

#!/bin/bash
IFS=$'
'
for i in $(cat /etc/hosts)
do
   echo $i
done

for 循环判断

#!/bin/bash
for ((i=0;i<100;i++))
do
   echo $i
done

for ((i=1;i<=100;i=i*2));do echo $i ;done

for 循环双数循环 #!/bin/bash

for ((a=9,b=1;a>1;a--,b++))
do
   echo $a $b
done

猜数脚本

#!/bin/bash
sj=$((RANDOM%100+1))
i=0
while true
do
read -p "please input num  1-100: " num
if [[ ! $num =~ ^[0-9]+$ ]];then
     echo "input error" 
     continue
fi
if [ $num -gt $sj ];then
    echo "输入大了"
elif [ $num -lt $sj ];then
    echo "输入小了"
else 
     echo "ok" 
     break
fi
let i++
done
cat <<EOF
输入错误 $i
输入次数 $(($i +1))
EOF