shell脚本快速入门之-----循环（for、while、until）

语句结构
for 变量名 in 取值列表
do
	命令序列
done

语句结构举例
for 收件人 in 邮件地址列表
do
	发送邮件
done

初始密码均设为123456
[root@localhost opt]# vim user.txt
zhangsan
lisi
wangermazi
zhaoliu
tianji
wangba
[root@localhost opt]# vim useradd.sh
#!/bin/bash
Lists=$(cat /opt/user.txt)
for bb in $Lists
do
        useradd $bb
        echo "123456" | passwd --stdin $bb
        echo "$bb添加成功"
done
[root@localhost opt]# chmod +x useradd.sh 
[root@localhost opt]# ./useradd.sh 
Changing password for user zhangsan.
passwd: all authentication tokens updated successfully.
zhangsan添加成功
useradd: warning: the home directory already exists.
Not copying any file from skel directory into it.
Creating mailbox file: File exists
Changing password for user lisi.
passwd: all authentication tokens updated successfully.
lisi添加成功
Changing password for user wangermazi.
passwd: all authentication tokens updated successfully.
wangermazi添加成功
Changing password for user zhaoliu.
passwd: all authentication tokens updated successfully.
zhaoliu添加成功
Changing password for user tianji.
passwd: all authentication tokens updated successfully.
tianji添加成功
Changing password for user wangba.
passwd: all authentication tokens updated successfully.
wangba添加成功
[root@localhost opt]# cat /etc/passwd | grep "bash"
root:x:0:0:root:/root:/bin/bash
dd:x:1000:1000:cn-tangzheng:/home/dd:/bin/bash
zhangsan:x:1001:1001::/home/zhangsan:/bin/bash
lisi:x:1002:1002::/home/lisi:/bin/bash
wangermazi:x:1003:1003::/home/wangermazi:/bin/bash
zhaoliu:x:1004:1004::/home/zhaoliu:/bin/bash
tianji:x:1005:1005::/home/tianji:/bin/bash
wangba:x:1006:1006::/home/wangba:/bin/bash

脚本可以适当修改优化：如
 echo "123456" | passwd --stdin $bb &> /dev/null

批量删除用户：在刚刚的基础上修改
[root@localhost opt]# vim useradd.sh
#!/bin/bash
Lists=$(cat /opt/user.txt)
for bb in $Lists
do
        userdel -r $bb	'-r 删除家目录'
        #echo "123456" | passwd --stdin $bb &> /dev/null
        echo "$bb删除成功"
done

[root@localhost opt]# ./useradd.sh 
zhangsan删除成功
lisi删除成功
wangermazi删除成功
zhaoliu删除成功
tianji删除成功
wangba删除成功
[root@localhost opt]# cat /etc/passwd | grep "bash"
root:x:0:0:root:/root:/bin/bash
dd:x:1000:1000:cn-tangzheng:/home/cn-tangzheng:/bin/bash

[root@localhost opt]# vim ipchk.sh 
#!/bin/bash
for ((i=1;i<=10;i++))
do
  ping -c 3 -i 0.2 -W 3 "192.168.197.$i" &> /dev/null
  if [ $? -eq 0 ]
        then
        echo "Host 192.168.197.$i is up"
  else
        echo "Host 192.168.197.$i is down"
  fi
done
[root@localhost opt]# ./ipchk.sh 
Host 192.168.197.1 is up
Host 192.168.197.2 is up
Host 192.168.197.3 is down
Host 192.168.197.4 is down
Host 192.168.197.5 is down
Host 192.168.197.6 is down
Host 192.168.197.7 is down
Host 192.168.197.8 is down
Host 192.168.197.9 is down
Host 192.168.197.10 is down

#!/bin/bash
for ((i=1;i<=10;i++))
do
        echo "$i"
done

#!/bin/bash
i=1
for ((;i<=10;i++))
do
        echo "$i"
done

#!/bin/bash
i=1
for ((;i<=10;))
do
        echo "$i"
        let i++
done

#!/bin/bash
i=1
for ((;;))
do
  if [ $i -le 10 ]
        then
        echo "$i"
        let i++
  else
        exit 0
  fi
done

[root@localhost opt]# ./number.sh 
1
2
3
4
5
6
7
8
9
10

语法格式
let 表达式
或
let "表达式"
或
let '表达式'
以上方式都等价于 ((表达式))

#!/bin/bash
sum=0
for((i=0;i<=10;i+=2))
  do
        let sum+=$i
  done
        echo "总和为：$sum"

#!/bin/bash
sum=0
for((i=1;i<=10;i+=2))
  do
        let sum+=$i
  done
        echo "总和为：$sum"

#!/bin/bash
sum=0
for((i=0;i<=10;i+=2))
  do
        if [ `expr $i % 2` -eq 0 ]
         then
           let sum+=$i
        fi
  done
        echo "总和为：$sum"

#!/bin/bash
sum=0
for((i=1;i<=10;i+=2))
  do
        if [ `expr $i % 2` -eq 1 ]
         then
           let sum+=$i
        fi
  done
        echo "总和为：$sum"

语句结构
while 条件测试操作
do
	命令序列
done

语句结构示例
while 未猜中正确的价格
do
	反复猜测商品价格
done

#!/bin/bash
i=0
while [ $i -le 10 ]
do
  echo "$i"
  let i++
  [root@localhost opt]# . cccc.sh 
0
1
2
3
4
5
6
7
8
9
10

while true：死循环有时候也有奇效，可与用户交互

#!/bin/bash
while true
do
  read -p "请输入yes退出：" KEY
  if [ $KEY = yes ]
        then
          break
  fi
done
echo "正常退出"

1
2
3
4
5
6
7
8
9
10
11
[root@localhost opt]# ./sixunhuan.sh 
请输入yes退出：no
请输入yes退出：1
请输入yes退出：d
请输入yes退出：！
请输入yes退出：a
请输入yes退出：yes
正常退出

#!/bin/bash
i=0
while [ $i -le 19 ]
do
  let i++
  useradd stu$i
  echo "123456" | passwd --stdin stu$i &> /dev/null
  echo "stu$i添加成功"
done
echo "添加完毕"

[root@localhost opt]# ./useradd.sh 
stu1添加成功
stu2添加成功
stu3添加成功
stu4添加成功
stu5添加成功
stu6添加成功
stu7添加成功
stu8添加成功
stu9添加成功
stu10添加成功
stu11添加成功
stu12添加成功
stu13添加成功
stu14添加成功
stu15添加成功
stu16添加成功
stu17添加成功
stu18添加成功
stu19添加成功
stu20添加成功
添加完毕

#!/bin/bash
A=`expr $RANDOM % 1000`
i=0
echo "商品的实际价格为0-999之间，猜猜看是多少？"
read -p "请输入你猜测的价格数目：" num
while [ $num -le 999 ] && [ $num -ge 1 ] 
do
        let i++
     if [ $num -eq $A ]
        then
        echo "恭喜你答对了，实际价格是$A"
        echo "你一共猜测了$i 次"
        exit 0
     elif [ $num -lt $A ]
        then
        echo "太低了"
        read -p "请输入你猜测的价格数目：" num
     else
        echo "太高了"
        read -p "请输入你猜测的价格数目：" num
     fi
  done

until 条件测试操作
do
 命令序列
done

while 未超过10
do
 数字依次增加
done

#!/bin/bash
i=1
S=0
until [ $i -eq 51 ]
do
 let S+=$i
 let i++

done
echo "$S"

[root@localhost opt]# ./jisuan.sh 
1275

#!/bin/bash
username=$1
#判断格式参数是否为空
if [ $# -lt 1 ]
 then
 echo "Usage:`basename $0` <username> [<message>]"
 exit 1
fi
#判断账号是否存在
if grep "^$username:" /etc/passwd &> /dev/nell;then :
  else
        echo "用户不存在"
        exit 2
fi
#判断用户是否在线
until who | grep "$username" &> /dev/null
do
        echo "用户不在线,正在尝试连接"
        sleep 3
done
mes=$*
echo "$mes" | write "$username"

[root@localhost opt]# ./mes.sh 
Usage:mes.sh <username> [<message>]
[root@localhost opt]# ./mes.sh wangwu
用户不存在
[root@localhost opt]# ./mes.sh stu1
用户不在线,正在尝试连接
用户不在线,正在尝试连接
^C