语法：for 变量名 in 条件; do …; done
案例1
#!/bin/bash
sum=0
for i in seq 1 100
do
? ? sum=$[$sum+$i]
? ? echo $i
done
echo $sum
案例2：
文件列表循环
#!/bin/bash
cd /etc/
for a in ls /etc/
do
? ? if [ -d $a ]
? ? then
? ?? ? ls -d $a
? ? fi
done

二：while循环

语法 while 条件; do … ; done
案例1
#!/bin/bash
while :
do
? ? load=w|head -1|awk -F ‘load average: ‘ ‘{print $2}‘|cut -d. -f1
? ? if [ $load -gt 10 ]
? ? then
? ?? ???top|mail -s "load is high: $load" [email?protected]
? ? fi
? ? sleep 30
done
案例2：
#!/bin/bash
while :
do
read -p "Please input a number: " n
if [ -z "$n" ]
then
echo "you need input sth."
continue
fi
n1=echo $n|sed ‘s/[0-9]//g‘
if [ -n "$n1" ]
then
echo "you just only input numbers."
continue
fi
break
done
echo $n

三：break跳出循环

#!/bin/bash
for i in seq 1 5
do
? ? echo $i
? ? if [ $i == 3 ]
? ? then
? ?? ???break
? ? fi
? ? echo $i
done
echo aaaaaaa

四：continue结束本次循环

忽略continue之下的代码，直接进行下一次循环
#!/bin/bash
for i in seq 1 5
do
? ? echo $i
? ? if [ $i == 3 ]
? ? then
? ?? ???continue
? ? fi
? ? echo $i
done
echo $i

五：exit退出整个脚本

#!/bin/bash
for i in seq 1 5do? ? echo $i? ? if [ $i == 3 ]? ? then? ?? ???exit? ? fi? ? echo $idoneecho aaaaaaa