shel ---条件、循环

最新推荐文章于 2022-09-07 19:01:10 发布

wuludan0217

最新推荐文章于 2022-09-07 19:01:10 发布

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文章标签： shell if语句 for循环

本文链接：https://blog.youkuaiyun.com/wuludan0217/article/details/85315675

版权

一、 if语句

if示例

#!/bin/bash
user=kiosk
if grep $user /etc/passwd;then
echo “Hello $user”
fi

if date;then
echo “Hello date”
fi

if-else示例

#!/bin/bash
user=student
if grep $user /etc/passwd;then
echo "The files for user $u s e r a r e : " l s - a / h o m e /$ user
else
echo “$user not exist!”
fi

if-elif-else示例

#!/bin/bash
if [ $1 == “student” ];then
echo “Welcome $1”
elif [ $1 == “westos” ];then
echo “Welcome $1”
elif [ $1 == “kiosk” ];then
echo “Welcome $1”
elif [ $1 == “linux” ];then
echo “Welcome $1”
else
echo “You are not allowed!”
fi

二、 for循环

生成1-5序列
第一种：

[root@localhost mnt]# awk 'BEGIN{for(i=1;i<=5;i++){print i}}'
1
2
3
4
5

第二种：

[root@localhost mnt]# vim for1.sh
for NUM in `seq 5`
do
     echo $NUM
done

[root@localhost mnt]# sh for1.sh 
1
2
3
4
5

第三种：

[root@localhost mnt]# vim for3.sh 
for ((A=1;A<=5;A++))
do
   echo $A
done

[root@localhost mnt]# sh for3.sh 
1
2
3
4
5

第四种：

[root@localhost mnt]# seq 5    ##seq命令可以直接生成
1
2
3
4
5
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40

生成奇数序列

[root@localhost mnt]# vim for2.sh
for NUM in `seq 1 2 10`
do
     echo $NUM
done
[root@server19 mnt]# sh for2.sh 
1
3
5
7
9
1
2
3
4
5
6
7
8
9
10
11

实例练习：
检测多台主机网络的通断

[root@localhost mnt]# vim ping.sh
#for ((a=1;a<60;a++))    ###三种写法任选一种
#for a in `seq 60`
for a in {1..60}
do
    ping -c1 -w1 172.25.254.$a &> /dev/null && echo 172.25.254.$a is up || echo 172.25.254.$a is down 
done
1
2
3
4
5
6
7

10s倒计时

[root@localhostmnt]# vim time.sh 
#!/bin/bash
for ((a=10;a>0;a--))
do 
	echo -n " TIME $a "    ##注意空格
	echo -ne "\r"
	sleep 1
done

用户输入分和秒，开始倒计时

[root@localhost mnt]# vim time.sh 
#!/bin/bash
read -p "please input minutes and seconds!" k j
a=$k*60+$j
for ((b=$a;b>0;b--))
do
	echo -n " Time $[$b/60]:$[$b%60] "
	echo -ne "\r"
	sleep 1
done

三、while循环

创建用户westos{1…20},并修改密码为123456

[root@localhost mnt]# vim while.sh
#!/bin/bash
PREFIX="westos"
i=1
while [ $i -le 20 ] 
do
	useradd ${PREFIX}$i
        echo "123456" | passwd --studin $[PREFIX]$i &> /dev/null
	((i++))
done

[root@localhost mnt]# ls /home/
student   westos11  westos14  westos17  westos2   westos4  westos7
westos1   westos12  westos15  westos18  westos20  westos5  westos8
westos10  westos13  westos16  westos19  westos3   westos6  westos9