Linux shell编程——if条件判断

墨蓝 2022-01-16 03:46 561阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

**if 语句格式**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if&nbsp;&nbsp;条件 then &nbsp;Command else &nbsp;Command fi&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;别忘了这个结尾</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">If语句忘了结尾fi test.sh: line 14: syntax error:&nbsp;unexpected end of fi</td> 
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**if 的三种条件表达式**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if command then if &nbsp;函数 then</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;命令执行成功，等于返回0 （比如grep ,找到匹配） 执行失败，返回非0 （grep,没找到匹配）</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if [ expression_r_r_r&nbsp;&nbsp;] then&nbsp;</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;表达式结果为真，则返回0，if把0值引向then</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if test expression_r_r_r then</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;表达式结果为假，则返回非0，if把非0值引向then</td> 
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**\[ \] && ——快捷if**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[ -f "/etc/shadow" ] &amp;&amp; echo "This computer uses shadow passwors"</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;&nbsp;&nbsp;&amp;&amp; 可以理解为then &nbsp;&nbsp;&nbsp;&nbsp;如果左边的表达式为真则执行右边的语句</td> 
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**shell的if与c语言if的功能上的区别**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;shell if</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;c语言if</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">0为真，走then</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;正好相反，非0走then</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;不支持整数变量直接if 必须:if [ i –ne 0 ] 但支持字符串变量直接if if [ str ] 如果字符串非0</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;支持变量直接if if (i )</td> 
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=================================以command作为if 条件===================================  
  
**以多条command或者函数作为if 条件**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">echo –n “input:” read user if 多条指令,这些命令之间相当于“and”（与） grep $user /etc/passwd &gt;/tmp/null&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; who -u | grep $user then&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;上边的指令都执行成功,返回值$?为0，0为真，运行then &nbsp;echo "$user has logged" else&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;指令执行失败，$?为1，运行else &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;echo "$user has not logged" fi&nbsp;&nbsp;&nbsp;</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;"># sh test.sh input : macg macg&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pts/0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;May 15 15:55&nbsp;&nbsp;&nbsp;.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2075 (192.168.1.100) macg has logged &nbsp;&nbsp;&nbsp; # sh test.sh input : ddd ddd has not logged&nbsp;&nbsp;</td> 
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**以函数作为if条件 (函数就相当于command,函数的优点是其return值可以自定义)**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if 以函数作为if条件， getyn then&nbsp;&nbsp;&nbsp;函数reture值0为真，走then echo " your answer is yes" else&nbsp;&nbsp;函数return值非0为假，走else echo "your anser is no" fi&nbsp;&nbsp;</td> 
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**if command 等价于 command+if $?**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">$ vi testsh.sh #!/bin/sh if cat 111-tmp.txt | grep ting1 then echo found else echo "no found" fi</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;$ vi testsh.sh #!/bin/sh cat 111-tmp.txt | grep ting1 if [ $? -eq 0 ] then echo $? echo found else echo $? echo "no found" fi</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">$ sh testsh.sh no found&nbsp;&nbsp;</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">$ sh testsh.sh 1 no found</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;vertical-align:top;">$ vi 111-tmp.txt that is 222file thisting1 is 111file $ sh testsh.sh thisting1 is 111file found</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;vertical-align:top;">$ vi 111-tmp.txt that is 222file thisting1 is 111file $ sh testsh.sh thisting1 is 111file 0 found</td> 
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========================================以条件表达式作为 if条件=============================  
  
**传统if 从句子——以条件表达式作为 if条件**  
if \[ 条件表达式 \]  
then  
command  
command  
command  
else  
command  
command  
fi  
  
 **条件表达式**

*  文件表达式

**if \[ -f file \] 如果文件存在**  
**if \[ -d ... \] 如果目录存在**  
**if \[ -s file \] 如果文件存在且非空**   
if \[ -r file \] 如果文件存在且可读  
if \[ -w file \] 如果文件存在且可写  
if \[ -x file \] 如果文件存在且可执行

*  整数变量表达式

**if \[ int1 -eq int2 \] 如果int1等于int2** 
**if \[ int1 -ne int2 \] 如果不等于** 
if \[ int1 -ge int2 \] 如果>= 
if \[ int1 -gt int2 \] 如果> 
if \[ int1 -le int2 \] 如果<= 
if \[ int1 -lt int2 \] 如果<

*  字符串变量表达式

If \[ $a = $b \] 如果string1等于string2  
**字符串允许使用赋值号做等号**  
if \[ $string1 != $string2 \] 如果string1不等于string2  
**if \[ -n $string \] 如果string 非空(非0），返回0(true)**  
if \[ -z $string \] 如果string 为空  
**if \[ $sting \] 如果string 非空，返回0 (和-n类似)**   
  
  
**条件表达式引用变量要带$**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if [ a = b ] ;then&nbsp;&nbsp;&nbsp;&nbsp; echo equal else echo no equal fi</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input a: 5 input b: 5 no equal&nbsp;&nbsp;（等于表达式没比较$a和$b,而是比较和a和b,自然a!=b)</td> 
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改正：

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if [ $a = $b ] ;then&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; echo equal else echo no equal fi</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input a: 5 input b: 5 equal</td> 
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**-eq -ne -lt -nt只能用于整数，不适用于字符串，字符串等于用赋值号=**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ vi test.sh echo -n "input your choice:" read var if&nbsp;&nbsp;[ $var -eq "yes" ] then echo $var fi [macg@machome ~]$ sh -x test.sh input your choice: y test.sh: line 3: test: y: integer expression_r_r_r expected &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;期望整数形式，即-eq不支持字符串</td> 
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**=放在别的地方是赋值,放在if \[ \] 里就是字符串等于,shell里面没有==的,那是c语言的等于**  
  
  
**无空格的字符串，可以加" ",也可以不加**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ vi test.sh echo "input a:" read a echo "input is $a" if [ $a = 123 ] ; then echo equal123 fi</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input a: 123 input is 123 equal123&nbsp;</td> 
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**= 作为等于时，其两边都必须加空格，否则失效**  
等号也是操作符，必须和其他变量，关键字，用空格格开 (等号做赋值号时正好相反，两边不能有空格）

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ vi test.sh echo "input your choice:" read var if [&nbsp;$var="yes"&nbsp;] then echo $var echo "input is correct" else echo $var echo "input error" fi</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ vi test.sh echo "input your choice:" read var if [&nbsp;$var = "yes"&nbsp;]&nbsp;&nbsp;&nbsp;在等号两边加空格 then echo $var echo "input is correct" else echo $var echo "input error" fi</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input your choice: y y input is correct [macg@machome ~]$ sh test.sh input your choice: n&nbsp;&nbsp;&nbsp;&nbsp; n input is correct&nbsp; 输错了也走then,都走then,为什么? 因为if把$var="yes"连读成一个变量，而此变量为空，返回1，则走else</td> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;[macg@machome ~]$ sh test.sh input your choice: y y input error [macg@machome ~]$ sh test.sh input your choice: no&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; no input error 一切正常</td> 
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**If \[ $ANS \] 等价于 if \[ -n $ANS \]**  
如果字符串变量非空（then） , 空(else)

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">echo "input your choice:" read ANS if [ $ANS ] then echo no empty else echo empth fi&nbsp;</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input your choice:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;回车 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; empth&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;说明“回车”就是空串 [macg@machome ~]$ sh test.sh input your choice: 34 no empty&nbsp;</td> 
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**整数条件表达式，大于，小于**，s**hell里没有> 和< ,会被当作尖括号，只有-ge,-gt,-le,lt**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ vi test.sh echo "input a:" read a if&nbsp;&nbsp;[ $a -ge 100 ] ; then echo 3bit else echo 2bit fi</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input a: 123 3bit [macg@machome ~]$ sh test.sh input a: 20 2bit</td> 
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**整数操作符号-ge,-gt,-le,-lt, 别忘了加-**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if&nbsp;&nbsp;test $a&nbsp;&nbsp;ge&nbsp;100 ; then [macg@machome ~]$ sh test.sh test.sh: line 4: test: ge: binary operator expected</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">if&nbsp;&nbsp;test $a -ge 100 ; then [macg@machome ~]$ sh test.sh input a: 123 3bit</td> 
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============================逻辑表达式=========================================  
  
 **逻辑非 ! 条件表达式的相反**  
if \[ ! 表达式 \]  
if \[ ! -d $num \] 如果不存在目录$num  
  
  
 **逻辑与 –a** **条件表达式的并列**  
if \[ 表达式1 –a 表达式2 \]  
  
  
**逻辑或 -o**  **条件表达式的或**  
if \[ 表达式1 –o 表达式2 \]  
  
  
**逻辑表达式**

*  表达式与前面的=
    
    != -d –f –x -ne -eq -lt等合用
 *  逻辑符号就正常的接其他表达式，没有任何括号（ ），就是并列

if \[ -z "$JHHOME" -a -d $HOME/$num \]

*  注意逻辑与-a与逻辑或-o很容易和其他字符串或文件的运算符号搞混了

**最常见的赋值形式，赋值前对=两边的变量都进行评测**  
左边测变量是否为空，右边测目录(值)是否存在（值是否有效）

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@mac-home ~]$ vi test.sh : echo "input the num:" read num echo "input is $num" if [ -z "$JHHOME" -a -d $HOME/$num ]&nbsp;&nbsp;&nbsp;如果变量$JHHOME为空，且$HOME/$num目录存在 then JHHOME=$HOME/$num&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;则赋值 fi echo "JHHOME is $JHHOME"&nbsp;&nbsp;</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;vertical-align:top;">----------------------- [macg@mac-home ~]$ sh test.sh input the num: ppp input is ppp JHHOME is 目录-d $HOME/$num&nbsp;&nbsp;&nbsp;不存在，所以$JHHOME没被then赋值</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;vertical-align:top;">[macg@mac-home ~]$ mkdir ppp [macg@mac-home ~]$ sh test.sh input the num: ppp input is ppp JHHOME is /home/macg/ppp</td> 
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**一个-o的例子，其中却揭示了”=”必须两边留空格的问题**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">echo "input your choice:" read ANS if [&nbsp;$ANS="Yes"&nbsp;-o $ANS="yes" -o $ANS="y" -o $ANS="Y" ] then ANS="y" else ANS="n" fi echo $ANS</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input your choice: n y [macg@machome ~]$ sh test.sh input your choice: no y 为什么输入不是yes,结果仍是y(走then） 因为=被连读了，成了变量$ANS="Yes"，而变量又为空，所以走else了</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ vi test.sh echo "input your choice:" read ANS&nbsp;&nbsp;&nbsp;&nbsp;echo "input your choice:" read ANS if [&nbsp;$ANS = "Yes"&nbsp;-o $ANS = "yes" -o $ANS = "y" -o $ANS = "Y" ] then ANS="y" else ANS="n" fi echo $ANS</td> 
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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ sh test.sh input your choice: no n [macg@machome ~]$ sh test.sh input your choice: yes y [macg@machome ~]$ sh test.sh input your choice: y y</td> 
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===================以 test 条件表达式 作为if条件===================================  
  
**if test $num -eq 0 等价于 if \[ $num –eq 0 \]**  
  
 **test 表达式,没有 \[ \]**  
if test $num -eq 0  
then  
echo "try again"  
else  
echo "good"  
fi  
  
 **man test**

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 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">[macg@machome ~]$ man test [(1)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;User Commands&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[(1) SYNOPSIS &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;test EXPRESSION &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[ EXPRESSION ] &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[-n] STRING &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;the length of STRING is nonzero&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-n和直接$str都是非0条件 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-z STRING &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;the length of STRING is zero &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;STRING1 = STRING2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;the strings are equal &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;STRING1 != STRING2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;the strings are not equal &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 -eq INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 is equal to INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 -ge INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 is greater than or equal to INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 -gt INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 is greater than INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 -le INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 is less than or equal to INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 -lt INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 is less than INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 -ne INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INTEGER1 is not equal to INTEGER2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE1 -nt FILE2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE1 is newer (modification date) than FILE2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE1 -ot FILE2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE1 is older than FILE2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-b FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is block special &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-c FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is character special &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-d FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is a directory &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-e FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;文件存在 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-f FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is a regular file&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;文件存在且是普通文件 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-h FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is a symbolic link (same as -L) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-L FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is a symbolic link (same as -h) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-G FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is owned by the effective group ID &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-O FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is owned by the effective user ID &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-p FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is a named pipe &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-s FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and has a size greater than zero &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-S FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is a socket &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-w FILE &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FILE exists and is writable &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;-x FILE FILE exists and is executable &nbsp;</td> 
 </tr> 
 </tbody> 
</table>

======================if简化语句=================================  
  
**最常用的简化if语句**

<table> 
 <tbody> 
 <tr> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;&nbsp;&nbsp;&amp;&amp; 如果是“前面”，则“后面” [ -f /var/run/dhcpd.pid ] &amp;&amp; rm /var/run/dhcpd.pid&nbsp;&nbsp;&nbsp;&nbsp;检查 文件是否存在，如果存在就删掉</td> 
 </tr> 
 <tr> 
 <td style="margin-left:0px;font-size:12px;font-family:Verdana, '宋体', sans-serif;line-height:18px;">&nbsp;&nbsp;&nbsp;||&nbsp;&nbsp;&nbsp;如果不是“前面”，则后面 [ -f /usr/sbin/dhcpd ] || exit 0&nbsp;&nbsp;&nbsp;&nbsp;检验文件是否存在，如果存在就退出</td> 
 </tr> 
 </tbody> 
</table>

**用简化 if 和$1,$2,$3来检测参数，不合理就调用help**  
**\[ -z "$1" \] && help 如果第一个参数不存在（-z 字符串长度为0 ）**  
\[ "$1" = "-h" \] && help 如果第一个参数是-h,就显示help  
  
  
**例子**  
\#!/bin/sh  
  
\[ -f "/etc/sysconfig/network-scripts/ifcfg-eth0" \] && rm -f /etc/sysconfig/network-scripts/ifcfg-eth0  
cp ifcfg-eth0.bridge /etc/sysconfig/network-scripts/ifcfg-eth0  
  
\[ -f "/etc/sysconfig/network-scripts/ifcfg-eth1" \] && rm -f /etc/sysconfig/network-scripts/ifcfg-eth1  
cp ifcfg-eth1.bridge /etc/sysconfig/network-scripts/ifcfg-eth1  
  
\[ -f "/etc/sysconfig/network-scripts/ifcfg-eth0:1" \] && rm -f /etc/sysconfig/network-scripts/ifcfg-eth0:1

转载于:https://my.oschina.net/u/994235/blog/202748

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220114/2da8e42ef3ed4595b8837ddb6326e298.png