語法：for 變量名 in 條件; do …; done

案例1
#!/bin/bash
sum=0
for i in seq 1 100
do
echo "$sum + $i"
sum=$[$sum+$i]
echo $sum
done
echo $sum

案例2
文件列表循環
#!/bin/bash
cd /etc/
for a in ls /etc/
do
if [ -d $a ]
then
ls $a
fi
done

操作過程

案例1

[root@linux-01 shell]# vim for1.sh
#!/bin/bash
sum=0
for i in seq 1 100
do
sum=$[$sum+$i]
done
echo $sum

[root@linux-01 shell]# sh for1.sh 
5050

案例2

[root@linux-01 shell]# vim for2.sh
#!/bin/bash
cd /etc/
for a in ls /etc/
do
[ -d $a ] && ls $a
done

20.11 while循環

語法 while 條件; 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]

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

操作過程

案例1

[root@linux-01 shell]# uptime|awk -F ‘load average:‘ ‘{print $2}‘
 0.00, 0.01, 0.05
[root@linux-01 shell]# uptime|awk -F ‘load average:‘ ‘{print $2}‘|cut -d . -f1
 0
[root@linux-01 shell]# uptime|awk -F ‘load average:‘ ‘{print $2}‘|cut -d . -f1|sed ‘s/ //‘
0
 

[root@linux-01 shell]# vim while1.sh
#!/bin/bash
while true
do
load= w|head -1|awk -F ‘load average: ‘ ‘{print $2}‘|cut -d . -f1
if [ $load -gt 10 ]
then
/usr/local/sbin/mail.py [email protected] "load high" "$load"
fi
sleep 30
done

案例2

[root@linux-01 shell]# vim while2.sh
#!/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

[root@linux-01 shell]# sh while2.sh 
Please input a number: sss
you just only input numbers.
Please input a number: ....
you just only input numbers.
Please input a number: 0
0

20.13 break跳出循環

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

操作過程

[root@linux-01 shell]# vim break.sh

#!/bin/bash
for i in seq 1 5
do
echo $i
if [ $i -eq 3 ]
then
break
fi
echo $i
done
echo aaaaaa

[root@linux-01 shell]# sh break.sh 
1
1
2
2
3
aaaaaa

20.14 continue結束本次循環

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

操作過程

[root@linux-01 shell]# vim continue.sh

#!/bin/bash
for i in seq 1 5
do
echo $i
if [ $i -eq 3 ]
then
continue
fi
echo $i
done
echo aaaaaa

[root@linux-01 shell]# sh continue.sh 
1
1
2
2
3
4
4
5
5
aaaaaa

20.15 exit退出整個腳本

[root@linux-01 shell]# vim exit.sh

#!/bin/bash
for i in seq 1 5
do
echo $i
if [ $i -eq 3 ]
then
exit
fi
echo $i
done
echo aaaaaa

[root@linux-01 shell]# sh exit.sh 
1
1
2
2
3

2018-05-31 Linux學習