linux shell 字符串操作

朴灿烈づ我的快乐病毒、 2022-11-17 14:50 181阅读 0赞

在做shell批处理程序时候，经常会涉及到字符串相关操作。有很多命令语句，如：awk,sed都可以做字符串各种操作。 其实shell内置一系列操作符号，可以达到类似效果，大家知道，使用内部操作符会省略启动外部程序等时间，因此速度会非常的快。

**一、判断读取字符串值**

> <table style="border:1px solid rgb(192,192,192); border-collapse:collapse">     
>  <thead> 
>   <tr> 
>    <th style="border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px"> 表达式</th> 
>    <th style="border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px"> 含义</th> 
>   </tr> 
>  </thead> 
>  <tbody> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 变量var的值, 与$var相同</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var-DEFAULT}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var没有被声明, 那么就以$DEFAULT作为其值 *</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var:-DEFAULT}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var没有被声明, 或者其值为空, 那么就以$DEFAULT作为其值 *</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var=DEFAULT}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var没有被声明, 那么就以$DEFAULT作为其值 *</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var:=DEFAULT}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var没有被声明, 或者其值为空, 那么就以$DEFAULT作为其值 *</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var+OTHER}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var声明了, 那么其值就是$OTHER, 否则就为null字符串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var:+OTHER}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var被设置了, 那么其值就是$OTHER, 否则就为null字符串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var?ERR_MSG}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var没被声明, 那么就打印$ERR_MSG *</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${var:?ERR_MSG}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果var没被设置, 那么就打印$ERR_MSG *</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${!varprefix*}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 匹配之前所有以varprefix开头进行声明的变量</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${!varprefix@}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 匹配之前所有以varprefix开头进行声明的变量</td> 
>   </tr> 
>  </tbody> 
> </table>

加入了“\*” 不是意思是： 当然, 如果变量var已经被设置的话, 那么其值就是$var.

> \[chengmo@localhost ~\]$ echo $\{abc-'ok'\}  
> ok  
> \[chengmo@localhost ~\]$ echo $abc
> 
> \[chengmo@localhost ~\]$ echo $\{abc='ok'\}  
> ok  
> \[chengmo@localhost ~\]$ echo $abc  
> ok
> 
> 如果abc 没有声明“=" 还会给abc赋值。
> 
> \[chengmo@localhost ~\]$ var1=11;var2=12;var3=  
> \[chengmo@localhost ~\]$ echo $\{!v@\}  
> var1 var2 var3  
> \[chengmo@localhost ~\]$ echo $\{!v\*\}  
> var1 var2 var3
> 
> $\{!varprefix\*\}与$\{!varprefix@\}相似，可以通过变量名前缀字符，搜索已经定义的变量,无论是否为空值。

**二、字符串操作（长度，读取，替换）**

> <table style="border:1px solid rgb(192,192,192); border-collapse:collapse">     
>  <thead> 
>   <tr> 
>    <th style="border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px"> 表达式</th> 
>    <th style="border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px"> 含义</th> 
>   </tr> 
>  </thead> 
>  <tbody> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${#string}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> $string的长度</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string:position}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 在$string中, 从位置$position开始提取子串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string:position:length}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 在$string中, 从位置$position开始提取长度为$length的子串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string#substring}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 从变量$string的开头, 删除最短匹配$substring的子串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string##substring}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 从变量$string的开头, 删除最长匹配$substring的子串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string%substring}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 从变量$string的结尾, 删除最短匹配$substring的子串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string%%substring}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 从变量$string的结尾, 删除最长匹配$substring的子串</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string/substring/replacement}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 使用$replacement, 来代替第一个匹配的$substring</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string//substring/replacement}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 使用$replacement, 代替<em>所有</em>匹配的$substring</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string/#substring/replacement}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果$string的<em>前缀</em>匹配$substring, 那么就用$replacement来代替匹配到的$substring</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> ${string/%substring/replacement}</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> 如果$string的<em>后缀</em>匹配$substring, 那么就用$replacement来代替匹配到的$substring</td> 
>   </tr> 
>   <tr> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>    <td style="font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; border:1px solid rgb(192,192,192); border-collapse:collapse; padding:3px; word-break:normal!important"> &nbsp;</td> 
>   </tr> 
>  </tbody> 
> </table>

**说明："\*** $substring”可以是一个*正则表达式*.

> **1.长度**
> 
> \[web97@salewell97 ~\]$ test='I love china'  
> \[web97@salewell97 ~\]$ echo $\{\#test\}  
> 12
> 
> $\{\#变量名\}得到字符串长度
> 
> **2.截取字串**
> 
> \[chengmo@localhost ~\]$ test='I love china'  
> \[chengmo@localhost ~\]$ echo $\{test:5\}  
> e china  
> \[chengmo@localhost ~\]$ echo $\{test:5:10\}  
> e china
> 
> $\{变量名:起始:长度\}得到子字符串
> 
> **3.字符串删除**
> 
> \[chengmo@localhost ~\]$ test='c:/windows/boot.ini'  
> \[chengmo@localhost ~\]$ echo $\{test\#/\}  
> c:/windows/boot.ini  
> \[chengmo@localhost ~\]$ echo $\{test\#\*/\}  
> windows/boot.ini  
> \[chengmo@localhost ~\]$ echo $\{test\#\#\*/\}  
> boot.ini
> 
> \[chengmo@localhost ~\]$ echo $\{test%/\*\}  
> c:/windows  
> \[chengmo@localhost ~\]$ echo $\{test%%/\*\}
> 
> $\{变量名\#substring正则表达式\}从字符串开头开始配备substring,删除匹配上的表达式。
> 
> $\{变量名%substring正则表达式\}从字符串结尾开始配备substring,删除匹配上的表达式。
> 
> 注意：$\{test\#\#\*/\},$\{test%/\*\} 分别是得到文件名，或者目录地址最简单方法。
> 
> **4.字符串替换**
> 
> \[chengmo@localhost ~\]$ test='c:/windows/boot.ini'  
> \[chengmo@localhost ~\]$ echo $\{test/\\//\\\\\}  
> c:\\windows/boot.ini  
> \[chengmo@localhost ~\]$ echo $\{test//\\//\\\\\}  
> c:\\windows\\boot.ini
> 
> $\{变量/查找/替换值\} 一个“/”表示替换第一个，”//”表示替换所有,当查找中出现了：”/”请加转义符”\\/”表示。

**三、性能比较**

> 在shell中，通过awk,sed,expr 等都可以实现，字符串上述操作。下面我们进行性能比较。
> 
> \[chengmo@localhost ~\]$ test='c:/windows/boot.ini'  
> \[chengmo@localhost ~\]$ time for i in $(seq 10000);do a=$\{\#test\};done;
> 
> real 0m0.173s  
> user 0m0.139s  
> sys 0m0.004s
> 
> \[chengmo@localhost ~\]$ time for i in $(seq 10000);do a=$(expr length $test);done;
> 
> real 0m9.734s  
> user 0m1.628s
> 
> 速度相差上百倍，调用外部命令处理，与内置操作符性能相差非常大。在shell编程中，尽量用内置操作符或者函数完成。使用awk,sed类似会出现这样结果。