Linux 之 shell 比较运算符

妖狐艹你老母 2022-06-10 02:08 185阅读 0赞

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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 运算符</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 描述</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 示例</td> 
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 <td colspan="3" style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 文件比较运算符</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -e&nbsp;filename</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename&nbsp;存在，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -e /var/log/syslog ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -d&nbsp;filename</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename&nbsp;为目录，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -d /tmp/mydir ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -f&nbsp;filename</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename&nbsp;为常规文件，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -f /usr/bin/grep ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -L&nbsp;filename</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename&nbsp;为符号链接，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -L /usr/bin/grep ]</td> 
 </tr> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -r&nbsp;filename</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename&nbsp;可读，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -r /var/log/syslog ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -w&nbsp;filename</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename&nbsp;可写，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -w /var/mytmp.txt ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -x&nbsp;filename</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename&nbsp;可执行，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -L /usr/bin/grep ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> filename1&nbsp;-nt&nbsp;filename2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename1&nbsp;比&nbsp;filename2&nbsp;新，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ /tmp/install/etc/services -nt /etc/services ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> filename1&nbsp;-ot&nbsp;filename2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;filename1&nbsp;比&nbsp;filename2&nbsp;旧，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ /boot/bzImage -ot arch/i386/boot/bzImage ]</td> 
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 <td colspan="3" style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 字符串比较运算符&nbsp;（请注意引号的使用，这是防止空格扰乱代码的好方法）</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -z&nbsp;string</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;string&nbsp;长度为零，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -z "$myvar" ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> -n&nbsp;string</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;string&nbsp;长度非零，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ -n "$myvar" ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> string1&nbsp;=&nbsp;string2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;string1&nbsp;与&nbsp;string2&nbsp;相同，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ "$myvar" = "one two three" ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> string1&nbsp;!=&nbsp;string2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 如果&nbsp;string1&nbsp;与&nbsp;string2&nbsp;不同，则为真</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ "$myvar" != "one two three" ]</td> 
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 <td colspan="3" style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 算术比较运算符</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> num1&nbsp;-eq&nbsp;num2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 等于</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ 3 -eq $mynum ]</td> 
 </tr> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> num1&nbsp;-ne&nbsp;num2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 不等于</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ 3 -ne $mynum ]</td> 
 </tr> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> num1&nbsp;-lt&nbsp;num2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 小于</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ 3 -lt $mynum ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> num1&nbsp;-le&nbsp;num2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 小于或等于</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ 3 -le $mynum ]</td> 
 </tr> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> num1&nbsp;-gt&nbsp;num2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 大于</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ 3 -gt $mynum ]</td> 
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 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> num1&nbsp;-ge&nbsp;num2</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 大于或等于</td> 
 <td style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> [ 3 -ge $mynum ] </td> 
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**算术运算符 **  
\+ - \* / % 表示加减乘除和取余运算  
\+= -= \*= /= 同 C 语言中的含义

**位操作符**

> >>= 表示位左右移一位操作  
& &= | |= 表示按位与、位或操作  
~ ! 表示非操作  
^ ^= 表示异或操作

**关系运算符 **

= == != 表示大于、小于、大于等于、小于等于、等于、不等于操作  
&& || 逻辑与、逻辑或操作

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 <td align="left" style="font-family:Arial; word-wrap:break-word; word-break:break-all; line-height:22px; visibility:visible!important; zoom:1!important"> 测试命令 test命令用于检查某个条件是否成立，它可以进行数值、字符和文件3个方面的测试，其测试符和相应的功能分别如下。 （1）数值测试： 　　-eq 等于则为真。 　　-ne 不等于则为真。 　　-gt 大于则为真。 　　-ge 大于等于则为真。 　　-lt 小于则为真。 　　-le 小于等于则为真。 （2）字串测试： 　　= 等于则为真。 　　!= 不相等则为真。 　　-z字串 字串长度伪则为真。 　　-n字串 字串长度不伪则为真。 （3）文件测试： 　　-e文件名 如果文件存在则为真。 　　-r文件名 如果文件存在且可读则为真。 　　-w文件名 如果文件存在且可写则为真。 　　-x文件名 如果文件存在且可执行则为真。 　　-s文件名 如果文件存在且至少有一个字符则为真。 　　-d文件名 如果文件存在且为目录则为真。 　　-f文件名 如果文件存在且为普通文件则为真。 　　-c文件名 如果文件存在且为字符型特殊文件则为真。 　　-b文件名 如果文件存在且为块特殊文件则为真</td> 
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**条件变量替换: **  
   Bash Shell可以进行变量的条件替换,既只有某种条件发生时才进行替换,替换   
条件放在\{\}中.   
(1) $\{value:-word\}

当变量未定义或者值为空时,返回值为word的内容,否则返回变量的值.

(2) $\{value:=word\}

与前者类似,只是若变量未定义或者值为空时,在返回word的值的同时将  word赋值给value

(3) $\{value:?message\}

若变量已赋值的话,正常替换.否则将消息message送到标准错误输出(若 此替换出现在Shell程序中,那么该程序将终止运行)

(4) $\{value:+word\}

若变量已赋值的话,其值才用word替换,否则不进行任何替换

(5) $\{value:offset\}

$\{value:offset:length\}  从变量中提取子串,这里offset和length可以是算术表达式.

(6) $\{\#value\}

变量的字符个数

(7) $\{value\#pattern\}

$\{value\#\#pattern\}   
       去掉value中与pattern相匹配的部分,条件是value的开头与pattern相匹配   
       \#与\#\#的区别在于一个是最短匹配模式,一个是最长匹配模式.

(8) $\{value%pattern\}

$\{value%%pattern\}   
       于(7)类似,只是是从value的尾部于pattern相匹配,%与%%的区别与\#与\#\#一样

(9) $\{value/pattern/string\}

$\{value//pattern/string\}   
       进行变量内容的替换,把与pattern匹配的部分替换为string的内容,/与//的区别与上同

注意: 上述条件变量替换中,除(2)外,其余均不影响变量本身的值

\#!/bin/bash

var1="1"  
var2="2"

下面是“**与**”运算符**-a**，另外注意，用一个test命令就可以了，还有if条件后面的分号

if test $var1 = "1"\-a $var2 = "2" ; then  
   echo "equal"  
fi

下面是“**或**”运算符 **-o**，有一个为真就可以

if test $var1 != "1" \-o $var2 != "3" ; then  
   echo "not equal"  
fi

下面是“**非**”运算符 **！**  
if条件是为真的时候执行，如果使用！运算符，那么原表达式必须为false

if ! test $var1 != "1"; then  
   echo "not 1"  
fi

以上三个if都为真，所以三个echo都会打印

**示例：**

**\[javascript\]**  [view plain][]   [copy][view plain]

[print][view plain] [?][view plain]

1.  \#!/bin/sh  
2.    
3.  aa="August 15, 2012"  
4.  bb="August 15, 20122"  
5.  cc="123"  
6.  dd="123"  
7.   
8.  \# -o  
9.  **if** \[ "$aa" = "$bb" -o "$cc" = "$dd" \]; then  
10.     echo "yes"  
11. **else**  
12.     echo "no"  
13. fi  
14.  
15. \# -a and !  
16. **if** \[ "$aa" != "$bb" -a "$cc" = "$dd" \]; then  
17.     echo "yes"  
18. **else**  
19.     echo "no"  
20. fi

**运行结果：**

true

\------------------------------------------------------------------------------------------------------

**shell字符串比较、判断是否为数字**

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 <div style="font-family:Arial; word-wrap:break-word; word-break:break-all; visibility:visible!important; zoom:1!important"> 
 二元比较操作符,比较变量或者比较数字.注意数字与字符串的区别. 1 整数比较 -eq&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;等于,如:if [ "$a" -eq "$b" ] 
 -ne&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;不等于,如:if [ "$a" -ne "$b" ] 
 -gt&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;大于,如:if [ "$a" -gt "$b" ] 
 -ge&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;大于等于,如:if [ "$a" -ge "$b" ] 
 -lt&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;小于,如:if [ "$a" -lt "$b" ] 
 -le&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;小于等于,如:if [ "$a" -le "$b" ] 
 &lt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;小于(需要双括号),如:(("$a" &lt; "$b")) 
 &lt;=&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;小于等于(需要双括号),如:(("$a" &lt;= "$b")) 
 &gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;大于(需要双括号),如:(("$a" &gt; "$b")) 
 &gt;=&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;大于等于(需要双括号),如:(("$a" &gt;= "$b")) 整数比较实例 
 
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 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> file='folder_url_top24/url_usa_top24_0'&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> fileSize=`ls&nbsp;-l&nbsp;folder_url_top24/url_usa_top24_0&nbsp;|&nbsp;awk&nbsp;-F&nbsp;'["&nbsp;"]'&nbsp;'{print&nbsp;$5}'`&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> FILESIZE=1000&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> #while&nbsp;[&nbsp;!&nbsp;-f&nbsp;$file&nbsp;-o&nbsp;"$fileSize"&nbsp;-lt&nbsp;"$FILESIZE"&nbsp;]&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> #while&nbsp;[&nbsp;!&nbsp;-f&nbsp;$file&nbsp;-o&nbsp;"$fileSize"&nbsp;-lt&nbsp;1000&nbsp;]&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> while&nbsp;(("$fileSize"&nbsp;&lt;&nbsp;1000))&nbsp;&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> do&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;"down&nbsp;again..."&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> done&nbsp;&nbsp;</li> 
 </ol> 
 </div> 其中，下面三种整数比较都成立： 
 
 1）&nbsp;while [ ! -f $file -o "$fileSize" -lt "$FILESIZE" ] 
 2）&nbsp;while [ ! -f $file -o "$fileSize" -lt 1000 ] 
 3）&nbsp;(("$fileSize" &lt; 1000)) 
 推荐使用第一种 2 字符串比较 =&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;等于,如:if [ "$a" = "$b" ] 
 ==&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;等于,如:if [ "$a" == "$b" ],与=等价 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;注意:==的功能在[[]]和[]中的行为是不同的,如下: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1 [[ $a == z* ]]&nbsp;&nbsp;&nbsp;&nbsp;# 如果$a以"z"开头(模式匹配)那么将为true &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2 [[ $a == "z*" ]] # 如果$a等于z*(字符匹配),那么结果为true &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4 [ $a == z* ]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;# File globbing 和word splitting将会发生 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5 [ "$a" == "z*" ] # 如果$a等于z*(字符匹配),那么结果为true &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;一点解释,关于File globbing是一种关于文件的速记法,比如"*.c"就是,再如~也是. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;但是file globbing并不是严格的正则表达式,虽然绝大多数情况下结构比较像. 
 !=&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;不等于,如:if [ "$a" != "$b" ] &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;这个操作符将在[[]]结构中使用模式匹配. 
 &lt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;小于,在ASCII字母顺序下.如: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if [[ "$a" &lt; "$b" ]] &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if [ "$a" \&lt; "$b" ] &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;注意:在[]结构中"&lt;"需要被转义. 
 &gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;大于,在ASCII字母顺序下.如: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if [[ "$a" &gt; "$b" ]] &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if [ "$a" \&gt; "$b" ] &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;注意:在[]结构中"&gt;"需要被转义. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;具体参考Example 26-11来查看这个操作符应用的例子. 
 -z&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;字符串为"null".就是长度为0 
 -n&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;字符串不为"null" 
 
 判断shell传入的参数个数是否为空： 
 
 <div style="font-family:Consolas,'Courier New',Courier,mono,serif; width:933.889px; overflow-y:hidden; overflow-x:auto; padding-top:1px; position:relative; margin:18px 0px!important; background-color:rgb(231,229,220)"> 
 <div style="padding-left:45px"> 
 <div style="padding:3px 8px 10px 10px; font-size:9px; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(153,153,153); background-color:rgb(248,248,248)"> 
 [python]&nbsp; 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="view plain" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">view plain</a> &nbsp; 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="copy" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">copy</a> 
 <div style="position:absolute; left:592px; top:5043px; width:32px; height:16px; z-index:99"> 
 </div> &nbsp; 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="print" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">print</a> 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="?" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">?</a> 
 </div> 
 </div> 
 <ol style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)"> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> #!/bin/bash&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> port=6379&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;命令行没参数，默认指定端口号为&nbsp;6379&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> if&nbsp;[&nbsp;$#&nbsp;-ge&nbsp;1&nbsp;];&nbsp;then&nbsp;&nbsp;&nbsp;#&nbsp;命令行参数个数大于等于1，则使用传入的参数port&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;port=$1&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;获取指定端口号&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> fi&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> echo&nbsp;"redis&nbsp;port:&nbsp;$port"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> redis-cli&nbsp;-h&nbsp;172.1628.10.114&nbsp;-p&nbsp;$port&nbsp;&nbsp;</li> 
 </ol> 
 </div> 
 
 
 
 字符串比较实例： 
 if [&nbsp;"$var1" = "$var2"&nbsp;] 
 代码： 
 
 <div style="font-family:Consolas,'Courier New',Courier,mono,serif; width:933.889px; overflow-y:hidden; overflow-x:auto; padding-top:1px; position:relative; margin:18px 0px!important; background-color:rgb(231,229,220)"> 
 <div style="padding-left:45px"> 
 <div style="padding:3px 8px 10px 10px; font-size:9px; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(153,153,153); background-color:rgb(248,248,248)"> 
 [css]&nbsp; 
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 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="copy" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">copy</a> 
 <div style="position:absolute; left:566px; top:5372px; width:32px; height:16px; z-index:99"> 
 </div> &nbsp; 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="print" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">print</a> 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="?" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">?</a> 
 </div> 
 </div> 
 <ol style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)"> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> #!/bin/sh&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> aa="August&nbsp;15,&nbsp;2012"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> bb="August&nbsp;15,&nbsp;2012"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> if&nbsp;[&nbsp;"$aa"&nbsp;=&nbsp;"$bb"&nbsp;];&nbsp;then&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;"yes"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> else&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;"no"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> fi&nbsp;&nbsp;</li> 
 </ol> 
 </div> 
 
 
 判断子字符串包含关系： =~ 
 代码： 
 
 <div style="font-family:Consolas,'Courier New',Courier,mono,serif; width:933.889px; overflow-y:hidden; overflow-x:auto; padding-top:1px; position:relative; margin:18px 0px!important; background-color:rgb(231,229,220)"> 
 <div style="padding-left:45px"> 
 <div style="padding:3px 8px 10px 10px; font-size:9px; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif; color:silver; border-left-width:3px; border-left-style:solid; border-left-color:rgb(153,153,153); background-color:rgb(248,248,248)"> 
 [python]&nbsp; 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="view plain" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">view plain</a> &nbsp; 
 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="copy" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">copy</a> 
 <div style="position:absolute; left:592px; top:5688px; width:32px; height:16px; z-index:99"> 
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 <a href="http://blog.csdn.net/ithomer/article/details/6836382#" title="print" style="color:rgb(160,160,160); text-decoration:none; border:none; padding:0px; margin:0px 10px 0px 0px; font-size:9px; background-color:inherit" rel="nofollow">print</a> 
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 </div> 
 </div> 
 <ol style="padding:0px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; background-color:rgb(255,255,255)"> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> a1="ithomer"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> a2="ithomer.net"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> a3="blog.ithomer.net"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> if&nbsp;[[&nbsp;"$a3"&nbsp;=~&nbsp;"$a1"&nbsp;]];&nbsp;then&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;"$a1是$a3的子串！"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> else&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;"$a1不是$a3的子串！"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> fi&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> if&nbsp;[[&nbsp;"$a3"&nbsp;=~&nbsp;"$a2"&nbsp;]];then&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;"$a2是$a3的子串！"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> else&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:rgb(85,85,85); line-height:20px; background-color:rgb(245,250,226)"> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;"$a2不是$a3的子串！"&nbsp;&nbsp;</li> 
 <li style="margin:0px!important; padding:0px 3px 0px 10px!important; border-style:none none none solid; border-left-width:3px; border-left-color:rgb(153,153,153); list-style:decimal-leading-zero outside; color:inherit; line-height:20px; background-color:rgb(245,250,226)"> fi&nbsp;&nbsp;</li> 
 </ol> 
 </div> 
 
 
 
 注意: 使用-n在[]结构中测试必须要用""把变量引起来.使用一个未被""的字符串来使用! -z或者就是未用""引用的字符串本身,放到[]结构中。虽然一般情况下可以工作,但这是不安全的.习惯于使用""来测试字符串是一种好习惯. 
 &nbsp;awk '{print $2}' class.txt | grep '^[0-9.]' &gt; res 
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