20.10 for循环 20.11/20.12 while循环 20.13 break跳出循环 20.14 continue结束本次循环 20.15 exit退出整个脚本

20.10 for循环

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]
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


for 循环时候会以空格或回车为分隔符
如图,  ls -l 文件其实只有3个, 1 , 2 , 3 4.txt, 但用for会分割成4个

20.11/20.12 while循环

语法 while 条件; do … ; done

案例1   //while : 表示死循环 , 也可以写成  while true 或 while 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" asldkfls@11.com
    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

20.13 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

20.14 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

20.15 exit退出整个脚本

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