【Shell】【学习笔记】Linux Shell脚本应用（六）

迷南。 2022-08-13 12:43 216阅读 0赞

课时6 条件测试

一、测试操作规范

测试的本质：

就是一条操作命令，并根据 $? 的值来判断条件是否成立。

测试操作规范：

格式1：test 条件表达式

格式2：\[ 条件表达式 \]

测试操作的练习方法：直接跟 && echo YES 判断结果。 返回YES，则表达式为真；没有返回结果，则表达式为假。方法如下：

\[ 条件表达式 \] && echo YES

示例1：测试/etc/grub是否为一个目录

\[ [root@localhost][root_localhost] ~\]\# \[ -d "/etc/grub" \] && echo YES

YES

二、文件状态的检测

存在及识别：

权限的检测：

<table style="font-size:undefined; border-collapse:collapse; margin-top:10px; margin-bottom:10px; background-color:inherit"> 
 <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">
      -r 
    </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">
      是否有读取（ 
     <span style="color:#ff0000; background-color:inherit">R</span>ead）权限 
    </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">
      -w 
    </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">
      是否有写入（ 
     <span style="color:#ff0000; background-color:inherit">W</span>rite）权限 
    </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">
      -x 
    </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">
      是否有可执行（e 
     <span style="color:#ff0000; background-color:inherit">X</span>cute）权限 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

示例1：测试/etc/fstab是否为一个文件

\[ [root@localhost][root_localhost] ~\]\# \[ -f "/etc/fstab" \] && echo YES

YES

\[ [root@localhost][root_localhost] ~\]\# \[ -f "/etc" \] && echo YES

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

示例2：测试/etc/shadow文件是否有相关权限

\[ [root@localhost][root_localhost] ~\]\# ls -l /etc/shadow

\- r--\------ 1 root root 1386 11-08 20:39 /etc/shadow

\[ [root@localhost][root_localhost] ~\]\# \[ -x "/etc/shadow" \] && echo YES //没有可执行权限

\[ [root@localhost][root_localhost] ~\]\# \[ -r "/etc/shadow" \] && echo YES //有读取权限

YES

\[ [root@localhost][root_localhost] ~\]\# \[ -w "/etc/shadow" \] && echo YES //有写入权限（所有者例外）

YES

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

三、整数值比较、字串匹配

整数值比较：数值1 比较操作符 数值2

<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">
      -eq 
    </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">
      等于（ 
     <span style="color:#ff0000; background-color:inherit">Eq</span>ual） 
    </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">
      -ne 
    </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">
      不等于 
     <span style="font-size:undefined; line-height:1.5">（<span style="color:#ff0000; background-color:inherit">N</span>ot&nbsp;<span style="color:#ff0000; background-color:inherit">E</span>qual）</span> 
    </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:35px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      -gt 
    </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:35px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit">
      大于（ 
     <span style="color:#ff0000; background-color:inherit">G</span>reater&nbsp; 
     <span style="color:#ff0000; background-color:inherit">T</span>han） 
    </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">
      -lt 
    </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"> 小于（<span style="color:#ff0000; background-color:inherit">L</span>esser&nbsp;<span style="color:#ff0000; background-color:inherit">T</span>han）</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">
      -ge 
    </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">
      大于或等于 
     <span style="font-size:undefined; line-height:1.5">（<span style="color:#ff0000; background-color:inherit">G</span>reater or&nbsp;<span style="color:#ff0000; background-color:inherit">E</span>qual）</span> 
    </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">
      -le 
    </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"> 小于或等于（<span style="color:#ff0000; background-color:inherit">L</span>esser or&nbsp;<span style="color:#ff0000; background-color:inherit">E</span>qual<span style="font-size:undefined; line-height:1.5">）</span></td> 
  </tr> 
 </tbody> 
</table>

字符串匹配：字符串1 比较操作符 字符串2

示例1：整数值比较，判断当前登陆用户数的情况

\[ [root@localhost][root_localhost] ~\]\# who | wc -l

\[ [root@localhost][root_localhost] ~\]\# \[ $( who | wc -l)  \-eq 2 \]  && echo YES

YES

\[ [root@localhost][root_localhost] ~\]\#  \[ $( who | wc -l)  \-gt 5 \]  && echo YES

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

示例2：字符串比较，判断当前登陆用户是否为root

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

root

\[ [root@localhost][root_localhost] ~\]\# \[ $USER = "root" \] && echo YES

YES