20.10 for loops
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 loop
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: $load" [email protected]
fi
sleep 30
done
案例2
#!/bin/bash
while :
do
read -p "Please input a number: " n
if [ -z "$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
20.13 break out of a loop
#!/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 to end this loop
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 exits the entire script
#!/bin/bash
for i in `seq 1 5`
do
echo $i
if [ $i == 3 ]
then
exit
fi
echo $i
done
echo aaaaaaa