Linux下的脚本中的函数及常用语句

1、脚本中的函数

变量：利用一串字符表示一个值

函数：利用一串字符表示一个动作

简化脚本内容，提高可读性，且可以循环调用

#实验：使用函数循环建立、删除用户，exit退出

[root@desktop mnt]# vim user_ctrl.sh
#!/bin/bash
ACTION_ADD(){
    [ "$1" = add ]&&{
    read -p "Please input your user name: " NAME
    read -p "Please input your user passwd: " -s PASSWD
    useradd $NAME
    echo $PASSWD | passwd --stdin $NAME
    }
}

ACTION_DEL(){
[ "$1" = del ]&&{
read -p "Please input your user name: " NAME
userdel -r $NAME
    }
}

USER_CTL()
{ read -p "Please input action: " ACTION
    [ "$ACTION" = exit ]&&{
    echo bye!
    exit 0
    }
    ACTION_ADD $ACTION
    ACTION_DEL $ACTION
    USER_CTL
}
USER_CTL

#测试：

2、常用的语句

exit直接退出

break退出当前循环，不影响其他

continue跳出本层循环，进入下一次循环

#实验：输出除4外的1～10

[root@desktop mnt]# vim test.sh
#!/bin/bash
for NUM in `seq 1 10`
do
while [ "$NUM" != "4" ]
File: /home/kiosk/Desktop/shell Page 6 of 7
do
echo $NUM
break
done
done

（1）for语句

for

do ***

done

[root@desktop mnt]# vim for.sh
#!bin/bash
for NUM in `seq 1 2 10` #使用seq可以设置步长
do
echo $NUM
done

[root@desktop mnt]# vim for.sh
#!bin/bash
for NUM in {1..5} #相当于 `seq 1 5` , 也相当于((NUM=1;NUM<=5;NUM++))
do
echo $NUM
done

#实验：显示教室中可连通的网络

[root@desktop mnt]# vim check_host.sh
#!/bin/bash
for IP in `seq 0 50`
do
ping -c1 -w1 172.25.254.$IP &> /dev/null && echo "172.25.254.$IP"
done

#实验：备份数据库

[root@desktop mnt]# vim mysql_dump.sh
#!/bin/bash
DATABASE=`mysql -uroot -EN -e "show databases;"|grep -E "^\*|schema$" -v`
mkdir -p /mnt/mysql_dump
for DATABASE in $DATABASE
do
    mysqldump -uroot $DATABASE > /mnt/mysql_dump/${DATABASE}.sql
    [ "$?" -eq "0" ]&&{
    echo -e "\033[32m$DATABASE is backuped!\033[0m"
    }
done

#测试：

[root@desktop mysql_backup]# sh mysql_dump.sh
linux is backuped!
mysql is backuped!
test is backuped!
westos is backuped!

（2）while do语句

while true

do ***

done

#实验：当根分区使用量超过30%时，向root用户发送邮件警告

[root@desktop mnt]# vim root_check.sh
#!/bin/bash
COUNT=`df|awk -F " " '/\/$/{print $5}'|awk -F "%" '{print $1}'`
while true
do
    [ "$COUNT" -ge "80" ]&&{
    echo Your / is full!| mail -s warning root
    }
sleep 1
done

#测试：

（3）if语句

if

*

then

*

elif

*

then

*

else

*

if

#实验：编写脚本判断文件类型

[root@desktop mnt]# vim file_check.sh
#!/bin/bash
Check_file()
{ if
[ "$1" "$2" ]
then
echo "$2" is $3
exit
fi
}
if
[ "$#" -ne "1" ]
then
echo -e "\033[31mPlease input a file name!\033[0m"
elif
[ ! -e "$1" ]
then
echo "$1 is not exist!"
else
Check_file -L $1 link
Check_file -f $1 "common file"
Check_file -S $1 socket
Check_file -b $1 block
Check_file -c $1 character
Check_file -d $1 directory
fi

#测试：

#实验：利用用户文件和密码文件建立用户，当文件数量不对报错，文件不存在时报错，文件行数差异时报错，用户存在时显示用户存在，不修改其密码，用户不存在时建立用户并设定密码

[root@desktop mnt]# vim user_create.sh
#!/bin/bash
if
[ "$#" -ne "2" ]
then
echo -e "\033[31mPlease input userfile and passfile!\033[0m"
exit 1
elif
[ ! -e "$1" ]
then
echo -e "\033[31m$1 is not exist!\033[0m"
exit 1
elif
[ ! -e "$2" ]
then
echo -e "\033[31m$2 is not exist!\033[0m"
exit 1
elif
USER_LINE=`awk 'BEGIN{N=0}//{N++}END{print N}' $1`
PASS_LINE=`awk 'BEGIN{N=0}//{N++}END{print N}' $2`
[ "$USER_LINE" -ne "$PASS_LINE" ]
then
echo -e "\033[31m The two file lines is different!\033[0m"
exit 1
else
for LINE_NUM in `seq 1 $USER_LINE`
do
USERNAME=`sed -n "${LINE_NUM}p" $1`
PASSWORD=`sed -n "${LINE_NUM}p" $2`
useradd $USERNAME&&{
echo $PASSWORD | passwd --stdin $USERNAME
}
done
fi

#测试：

（4）case语句

主要用于字符匹配型问题，解决该类问题时，相比于if语句速度快

#实验：输入dog时，输出cat；输入cat时，输出dog；其他输出error

[root@desktop mnt]# vim test.sh
#!/bin/bash
case $1 in
dog)
echo cat
;;
cat)
echo dog
;;
*)
echo error
esac

#测试：

（5）expect

#实验：编写脚本，使用ssh直接连接其他主机

[root@desktop mnt]# yum install expect -y
[root@desktop mnt]# which expect
/usr/bin/expect
[root@desktop mnt]# vim auto_connect.exp
#!/usr/bin/expect
set timeout 5
set IP [ lindex $argv 0 ]
set PASS [ lindex $argv 1 ]
spawn ssh root@$IP
expect {
"connecting" { send "yes\r";exp_continue}
"password" { send "$PASS\r"}
}
interact
[root@desktop mnt]# chmod +x /mnt/auto_connect.exp
[root@desktop mnt]# /mnt/auto_connect.exp 172.25.254.167 redhat

#测试：