基于linux下的shell中的变量

1、shell中的变量

（1）环境级
[[email protected] ~]# export a=1 #export作声明
[[email protected] ~]# echo $a
1
[[email protected] ~]# su - student
[[email protected] ~]$ echo $a #为空
（2）用户级
[[email protected] ~]# vim .bash_profile
export a=1
[[email protected] ~]# source .bash_profile #刷新
[[email protected] ~]# echo $a

1

[[email protected] ~]# su - student

[[email protected] ~]$ echo $a #为空

（3）系统级
[[email protected] ~]# vim /etc/profile
export a=3
[[email protected] ~]# source /etc/profile
[[email protected] ~]# echo $a
3
[[email protected]esktop ~]# exit
[[email protected] ~]# echo $a #显示的是用户级的变量，这是因为用户级配置文件后被加载，所以其生效
2

2、

[[email protected] ~]# echo $PS1

[\[email protected]\h \W]\$
[[email protected] ~]# PS1='westos>'
westos/u>PS1='westos\u>'
westosroot>PS1='westos \u>'
westos root>PS1='westos \w>' #w绝对路径
westos ~>cd /etc/sysconfig/
westos /etc/sysconfig>PS1='westos \W>' #W相对路径
westos sysconfig>cd /etc/sysconfig/

westos sysconfig>exit

3、变量的转义
\是单个的，""是批量的，

''为\的批量，称为强引用，可以引用所有字符，包括！、\、`、$这四个字符

4、变量值的传递
$n 脚本后跟的第n串字符
$# 脚本后所跟字符数的个数
$* 脚本后跟的所有字符串，其后字符默认为一串

[email protected] 脚本后跟的所有字符串，其后字符默认为三串

实验：利用脚本使用用户和密码文件建立用户，当文件不够时给出提醒
[[email protected] mnt]# vim password
[[email protected] mnt]# vim username
[[email protected] mnt]# vim user.sh
[ "$#" -ne "2" ]&&{
        echo "Please give me userfile and passwordfile"  
        exit 1
} #当脚本执行是其后字符数不等于2时提醒
MAX_LINE=`wc -l $1|cut -d " " -f 1`
for LINE_NUM in `seq 1 $MAX_LINE`
do
        USERNAME=`sed -n "${LINE_NUM}p" $1`
        PASSWORD=`sed -n "${LINE_NUM}p" $2`
        useradd $USERNAME
        echo $PASSWORD | passwd --stdin $USERNAME

done

5、read实现变量传递

实验：交互式判断ip是否可以ping通
[[email protected] mnt]# vim read.sh
read -p   "Please input ip: " （-s） ip #-p表示提示，-s表示用户输入时内容不可见

ping -c1 -w1 $ip &> /dev/null && echo $ip is up || echo $ip is down

实验：利用脚本建立用户，交互式输入用户文件和密码文件，当文件不存在时给出提醒
[[email protected] mnt]# vim user.sh
#!/bin/bash
read -p "Please input userfile: " userfile
[ -e "$userfile" ]||{
        echo "This file is not exit!"
        exit 1
}

read -p "Please input passfile: " passfile
[ -e "$passfile" ]||{
        echo "This file is not exit!"
        exit 1
}

MAX_LINE=`wc -l $userfile|cut -d " " -f 1`
for LINE_NUM in `seq 1 $MAX_LINE`
do
        USERNAME=`sed -n "${LINE_NUM}p" $userfile`
        PASSWORD=`sed -n "${LINE_NUM}p" $passfile`
        useradd $USERNAME
        echo $PASSWORD | passwd --stdin $USERNAME

done

6、系统中命令别名的设定
[[email protected] ~]# alias xie='vim' #临时设定别名
[[email protected] ~]# xie file
[[email protected] ~]# su - student
[[email protected] ~]$ xie
bash: xie: command not found...
[[email protected] ~]$ exit

logout

[[email protected] ~]# vim .bashrc #root用户永久设定别名
[[email protected] ~]# source .bashrc
[[email protected] ~]# xie file
[[email protected] ~]# su - student
[[email protected] ~]$ xie
bash: xie: command not found...
[[email protected] ~]$ exit

logout

[[email protected] ~]# vim /etc/bashrc #系统永久设定别名
[[email protected] ~]# source /etc/bashrc
[[email protected] ~]# xie file
[[email protected] ~]# su - student

[[email protected] ~]$ xie file

[[email protected] ~]# vim .bashrc #取消设定别名
[[email protected] ~]# vim /etc/bashrc
[[email protected] ~]# source .bashrc
[[email protected] ~]# source /etc/bashrc
[[email protected] ~]# xie file #删除文件中的设定行仍然成立，因为原有的设定不会被覆盖
[[email protected] ~]# unalias xie #撤销命令别名设定
[[email protected] ~]# xie file
bash: xie: command not found...

7、exit退出值

利用命令执行结果设定变量
Hostname=$(hostname)
Hostname=`hostname`

$?是命令在执行完成后产生的退出值，范围是[0-255]
$?=0时表示命令执行没有错误输出，这个值可以用exit命令执行，如exit66

实验：利用退出值判断ip是否通
[[email protected] mnt]# vim ip_check.sh
read -p "Please input ip: " ip
ping -c1 -w1 $ip &> /dev/null
B="$?" #返回值赋给B
echo exit="$B"
[ "$B" -eq "0" ]&&{ #退出值等于0时表示通
        echo "$ip is up"
}||{
        echo "$ip is down"

}

测试：
[[email protected] mnt]# sh ip_check.sh
Please input ip: 172.25.254.68   
exit=1
172.25.254.68 is down
[[email protected] mnt]# sh ip_check.sh
Please input ip: 172.25.254.25
exit=0
172.25.254.25 is up

8、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
可以循环调用

实验：循环建立、删除用户，exit退出
#!/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：
[[email protected] mnt]# sh user_ctrl.sh
Please input action: add
Please input your user name: haha
Please input action: exit
bye!
[[email protected] mnt]# id haha
uid=1011(haha) gid=1011(haha) groups=1011(haha)
[[email protected] mnt]# sh user_ctrl.sh
Please input action: del
Please input your user name: haha
Please input action: exit
bye!
[[email protected] mnt]# id haha
id: haha: no such user