【Shell】【学习笔记】Linux Shell脚本应用（三）

迈不过友情╰ 2022-08-13 12:42 245阅读 0赞

**课时3 使用变量**

一、变量基本操作

定义及赋值：变量名=变量值

引用变量：$变量名 或 $\{变量名\}

示例1：

\[ [root@localhost][root_localhost] ~\]\# Title=BeiDaQingNiao

\[ [root@localhost][root_localhost] ~\]\# echo $Title

BeiDaQingNiao

二、双引号/单引号/反撇号

<table style="font-size:undefined; border-collapse:collapse; margin-top:10px; margin-bottom:10px; background-color:inherit; width:600px"> 
 <tbody style="background-color:inherit"> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      双引号 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      允许引用、\转义 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      单引号 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      禁止引用、\转义 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      反撇号 或者&nbsp; 
     <span style="color:#ff0000; background-color:inherit">$()</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      以命令输出进行替换 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

示例1：\[接上一节的示例\]单引号和双引号 （双引号一般可省略）

\[ [root@localhost][root_localhost] ~\]\# echo "$Title Group."

BeiDaQingNiao Group.

\[ [root@localhost][root_localhost] ~\]\# echo ' $Title Group.'

$Title Group.

示例2：反撇号或 $()

\[ [root@localhost][root_localhost] ~\]\# uname -r

2.6.18-194.e5

\[ [root@localhost][root_localhost] ~\]\# Ver=\`uname -r\`

\[ [root@localhost][root_localhost] ~\]\# echo $Ver

2.6.18-194.e5

三、常见的环境变量

定义：用来记录/设置运行参数

示例1：显示当前系统中的环境变量

\[ [root@localhost][root_localhost] ~\]\# env

HOSTNAME=localhost.benet.com

SHELL=/bin/bash

HOME=/root

LOGNAME=root

......

四、其他特殊变量

由系统或脚本操控，不可直接赋值，如下所示：

<table style="font-size:undefined; border-collapse:collapse; margin-top:10px; margin-bottom:10px; background-color:inherit; width:598px"> 
 <tbody style="background-color:inherit"> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:96px"> 
    <div style="min-width:2px; background-color:inherit">
      $? 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:460px"> 
    <div style="min-width:2px; background-color:inherit">
      前一条命令的状态值，0为正常，非0为异常 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:96px"> 
    <div style="min-width:2px; background-color:inherit">
      $0 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:460px"> 
    <div style="min-width:2px; background-color:inherit">
      脚本自身的程序名 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:96px"> 
    <div style="min-width:2px; background-color:inherit">
      $1-$9 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:460px"> 第1-第9个位置参数</td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:96px"> 
    <div style="min-width:2px; background-color:inherit">
      $* 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:460px"> 
    <div style="min-width:2px; background-color:inherit">
      命令行的所有位置参数的内容 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:96px"> 
    <div style="min-width:2px; background-color:inherit">
      $# 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:460px"> 
    <div style="min-width:2px; background-color:inherit">
      命令行的位置参数个数 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

示例1：$?的使用

\[ [root@localhost][root_localhost] ~\]\# mkdir /mulua

\[ [root@localhost][root_localhost] ~\]\# echo $?

\[ [root@localhost][root_localhost] ~\]\# mkdir /mulua/a

mkdir: 无法创建目录”/mulu/a“：没有那个文件或目录

\[ [root@localhost][root_localhost] ~\]\# echo $?

示例2： $0、 $1-$9、 $\*、 $\#的使用

\[ [root@localhost][root_localhost] ~\]\# cat test.sh

@!/bin/bash

echo "本程序名： $0"

echo "执行时一共输入 $\# 个位置参数"

echo "其中第一个参数是： $1"