shell脚本中$0 $1 $# $@ $* $? $$ 的各种符号意义详解

﹏ヽ暗。殇╰゛Y 2022-09-09 13:59 257阅读 0赞

![7906fcd85e9240429cceb0a64f361023.png][]

## 一、概述 ##

shell中有两类字符：普通字符、元字符。

### 1. 普通字符 ###

在Shell中除了本身的字面意思外没有其他特殊意义，即普通纯文本；

### 2. 元字符 ###

是Shell的保留字符，在Shell中有着特殊的含义。  
![2ef32c1ce3654484b236af25368bdab1.png][]  
![71cd5d51140f4c07a2cee5a4d9d90f45.png][]

今天主要介绍一下shell中字符`$`的各种用法。

## 二、转义字符$ ##

在linux shell脚本中经常用到字符`$`，下面是`$`的一些常见用法

<table> 
 <thead> 
  <tr> 
   <th>名称</th> 
   <th align="left">含义</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>$#</td> 
   <td align="left">传给脚本的参数个数</td> 
  </tr> 
  <tr> 
   <td>$0</td> 
   <td align="left">脚本本身的名字</td> 
  </tr> 
  <tr> 
   <td>$1</td> 
   <td align="left">传递给该shell脚本的第一个参数</td> 
  </tr> 
  <tr> 
   <td>$2</td> 
   <td align="left">传递给该shell脚本的第二个参数</td> 
  </tr> 
  <tr> 
   <td>$@</td> 
   <td align="left">传给脚本的所有参数的列表</td> 
  </tr> 
  <tr> 
   <td>$*</td> 
   <td align="left">以一个单字符串显示所有向脚本传递的参数，与位置变量不同，参数可超过9个</td> 
  </tr> 
  <tr> 
   <td>$$</td> 
   <td align="left">脚本运行的当前进程ID号</td> 
  </tr> 
  <tr> 
   <td>$?</td> 
   <td align="left">显示最后命令的退出状态，0表示没有错误，其他表示有错误</td> 
  </tr> 
 </tbody> 
</table>

### 实例1 ###

建立脚本peng.sh如下：

#/bin/bash
    total=$[ $1 * $2 + $3 ]
    echo "$1 * $2 + $3 = $total"

运行如下：

./peng.sh 4 5 6

结果如下：  
![efcc46bc1fb845e898a37da989107ef9.png][]

### 实例2 ###

当把字符串输入给shell脚本的时候，注意是以空格作为分隔符，如果字符串本身就有空格的话，那么用双引号或者单引号，比如

#/bin/bash
    echo "$1 is pretty nice!"

运行如下：

./peng.sh 一口Linux

结果如下：  
![0a6cf9231486414a8095f6dd113a2c7d.png][]

### 实例3 ###

#!/bin/sh
    echo "参数个数:$#"
    echo "脚本名字:$0"
    echo "参数1:$1"
    echo "参数2:$2"
    echo "所有参数列表:$@"
    echo "pid:$$"
    if [ $1 = 100 ]
    then
     echo "命令退出状态：$?" 
     exit 0 #参数正确，退出状态为0
    else
     echo "命令退出状态：$?"
     exit 1 #参数错误，退出状态1
    fi

执行结果：  
![37e37dd76e0f42eb8e7c4c0bb3aab3cd.png][]

### 实例4 ###

使用for循环进行参数遍历

示例：

#!/bin/bash
    number=65             #定义一个退出值
    index=1               #定义一个计数器
    if [ -z "$1" ];then   #对用户输入的参数做判断，如果未输入参数则返回脚本的用法并退出，退出值65
       echo "Usage:$0 + 参数"
       exit $number
    fi
    echo "listing args with \$*:"    #在屏幕输入，在$*中遍历参数
    for arg in $*                                          
    do
       echo "arg: $index = $arg"                 
       let index+=1
    done
    echo
    index=1                         #将计数器重新设置为1
    echo "listing args with \"\$@\":"    #在"$@"中遍历参数
    for arg in "$@"
    do
       echo "arg: $index = $arg"
       let index+=1
    done

![36d83bdde0524001a910df7a8c9c3083.png][]  
![2a8ad08662864bc293b3c520e486c473.png][]

### 实例5 ###

小技巧1：在" ∗ " 和 \*"和 ∗"和\*中遍历参数的区别

示例：

#!/bin/bash
    number=11
    if [ $# -eq 0 ];then
       echo "Usage: $0 + 参数"
       exit $number
    fi
    for i in $*               #在$*中遍历参数，此时每个参数都是独立的，会遍历$#次
    do
       echo $i
    done
    echo
    for i in "$*"            #在"$*"中遍历参数，此时"$*"被扩展为包含所有位置参数的单个字符串，只遍历一次
    do
       echo $i
    done

![325ec497200142f98be97ec17d2c9cf3.png][]

## 三、linux命令执行返回值\*\*$?\*\*说明 ##

在 Linux 下，不管你是启动一个桌面程序也好，还是在控制台下运行命令，所有的程序在结束时，都会返回一个数字值，这个值叫做返回值，或者称为错误号 ( Error Number )。

### 1. 在控制台下，有一个特殊的环境变量 $?，保存着前一个程序的返回值，我们可以试试： ###

![e8088a5b93c3426fbbdc4f28e7846553.png][]

先随便执行个命令，比如像上面的 ls 某些文件，然后通过 echo $?，打印 $? 的值～

**我们发现返回值是 0，这是什么意思呢？**  
只要返回值是 0，就代表程序执行成功了～  
也就是说，如果 $? 变量的值不是 0 的话，就表示上一个命令在执行的过程中出错了。

### 2. 我们可以试着 ls 一个不存在的文件： ###

![477dc82c33be48e08841725c77a0c2b2.png][]

这样，对于某些打印出一堆不熟悉的英文信息的命令，可以方便的看出它是否成功执行结束。  
不过，每次都 echo $? 一下太累了，没关系，你可以把 $? 放在提示符里去：

### 3. 将上次命令执行是否成功的返回值放到提示符里面去：`export PS1="[\$?]${PS1}"` ###

root@ubuntu:/home/peng/zhh# export PS1="[\$?]${PS1}"
    [0]root@ubuntu:/home/peng/zhh# ls

![4d6b63d257da4de185bb4abc117f07ee.png][]

`export PS1="[\$?]${PS1}"` 这个命令把 **$?** 的值放在的提示符的最前面，这样每次执行完命令，这个值都会自动更新，这下就一目了然了～

### 4. 用perror查看错误提示 ###

那么如果返回的值不是 0，我们要怎么知道是那里出错了呢？  
大多数的程序出错都会给出提示，如果没有提示的话，可以用 perror 这个程序来查看错误的信息，比如返回值是 2，我们可以运行下面命令：

$ perror 2
    OS error code   2:  No such file or directory

这样就清楚了，原来是文件不存在～

> 该命令需要安装  
> apt-get install perror

### 5. 给出错误代码及其具体原因对照表： ###

"OS error code   1:  Operation not permitted"
    "OS error code   2:  No such file or directory"
    "OS error code   3:  No such process"
    "OS error code   4:  Interrupted system call"
    "OS error code   5:  Input/output error"
    "OS error code   6:  No such device or address"
    "OS error code   7:  Argument list too long"
    "OS error code   8:  Exec format error"
    "OS error code   9:  Bad file descriptor"
    "OS error code  10:  No child processes"
    "OS error code  11:  Resource temporarily unavailable"
    "OS error code  12:  Cannot allocate memory"
    "OS error code  13:  Permission denied"
    "OS error code  14:  Bad address"
    "OS error code  15:  Block device required"
    "OS error code  16:  Device or resource busy"
    "OS error code  17:  File exists"
    "OS error code  18:  Invalid cross-device link"
    "OS error code  19:  No such device"
    "OS error code  20:  Not a directory"
    "OS error code  21:  Is a directory"
    "OS error code  22:  Invalid argument"
    "OS error code  23:  Too many open files in system"
    "OS error code  24:  Too many open files"
    "OS error code  25:  Inappropriate ioctl for device"
    "OS error code  26:  Text file busy"
    "OS error code  27:  File too large"
    "OS error code  28:  No space left on device"
    "OS error code  29:  Illegal seek"
    "OS error code  30:  Read-only file system"
    "OS error code  31:  Too many links"
    "OS error code  32:  Broken pipe"
    "OS error code  33:  Numerical argument out of domain"
    "OS error code  34:  Numerical result out of range"
    "OS error code  35:  Resource deadlock avoided"
    "OS error code  36:  File name too long"
    "OS error code  37:  No locks available"
    "OS error code  38:  Function not implemented"
    "OS error code  39:  Directory not empty"
    "OS error code  40:  Too many levels of symbolic links"
    "OS error code  42:  No message of desired type"
    "OS error code  43:  Identifier removed"
    "OS error code  44:  Channel number out of range"
    "OS error code  45:  Level 2 not synchronized"
    "OS error code  46:  Level 3 halted"
    "OS error code  47:  Level 3 reset"
    "OS error code  48:  Link number out of range"
    "OS error code  49:  Protocol driver not attached"
    "OS error code  50:  No CSI structure available"
    "OS error code  51:  Level 2 halted"
    "OS error code  52:  Invalid exchange"
    "OS error code  53:  Invalid request descriptor"
    "OS error code  54:  Exchange full"
    "OS error code  55:  No anode"
    "OS error code  56:  Invalid request code"
    "OS error code  57:  Invalid slot"
    "OS error code  59:  Bad font file format"
    "OS error code  60:  Device not a stream"
    "OS error code  61:  No data available"
    "OS error code  62:  Timer expired"
    "OS error code  63:  Out of streams resources"
    "OS error code  64:  Machine is not on the network"
    "OS error code  65:  Package not installed"
    "OS error code  66:  Object is remote"
    "OS error code  67:  Link has been severed"
    "OS error code  68:  Advertise error"
    "OS error code  69:  Srmount error"
    "OS error code  70:  Communication error on send"
    "OS error code  71:  Protocol error"
    "OS error code  72:  Multihop attempted"
    "OS error code  73:  RFS specific error"
    "OS error code  74:  Bad message"
    "OS error code  75:  Value too large for defined data type"
    "OS error code  76:  Name not unique on network"
    "OS error code  77:  File descriptor in bad state"
    "OS error code  78:  Remote address changed"
    "OS error code  79:  Can not access a needed shared library"
    "OS error code  80:  Accessing a corrupted shared library"
    "OS error code  81:  .lib section in a.out corrupted"
    "OS error code  82:  Attempting to link in too many shared libraries"
    "OS error code  83:  Cannot exec a shared library directly"
    "OS error code  84:  Invalid or incomplete multibyte or wide character"
    "OS error code  85:  Interrupted system call should be restarted"
    "OS error code  86:  Streams pipe error"
    "OS error code  87:  Too many users"
    "OS error code  88:  Socket operation on non-socket"
    "OS error code  89:  Destination address required"
    "OS error code  90:  Message too long"
    "OS error code  91:  Protocol wrong type for socket"
    "OS error code  92:  Protocol not available"
    "OS error code  93:  Protocol not supported"
    "OS error code  94:  Socket type not supported"
    "OS error code  95:  Operation not supported"
    "OS error code  96:  Protocol family not supported"
    "OS error code  97:  Address family not supported by protocol"
    "OS error code  98:  Address already in use"
    "OS error code  99:  Cannot assign requested address"
    "OS error code 100:  Network is down"
    "OS error code 101:  Network is unreachable"
    "OS error code 102:  Network dropped connection on reset"
    "OS error code 103:  Software caused connection abort"
    "OS error code 104:  Connection reset by peer"
    "OS error code 105:  No buffer space available"
    "OS error code 106:  Transport endpoint is already connected"
    "OS error code 107:  Transport endpoint is not connected"
    "OS error code 108:  Cannot send after transport endpoint shutdown"
    "OS error code 109:  Too many references: cannot splice"
    "OS error code 110:  Connection timed out"
    "OS error code 111:  Connection refused"
    "OS error code 112:  Host is down"
    "OS error code 113:  No route to host"
    "OS error code 114:  Operation already in progress"
    "OS error code 115:  Operation now in progress"
    "OS error code 116:  Stale NFS file handle"
    "OS error code 117:  Structure needs cleaning"
    "OS error code 118:  Not a XENIX named type file"
    "OS error code 119:  No XENIX semaphores available"
    "OS error code 120:  Is a named type file"
    "OS error code 121:  Remote I/O error"
    "OS error code 122:  Disk quota exceeded"
    "OS error code 123:  No medium found"
    "OS error code 124:  Wrong medium type"
    "OS error code 125:  Operation canceled"
    "OS error code 126:  Required key not available"
    "OS error code 127:  Key has expired"
    "OS error code 128:  Key has been revoked"
    "OS error code 129:  Key was rejected by service"
    "OS error code 130:  Owner died"
    "OS error code 131:  State not recoverable"
    "MySQL error code 132: Old database file"
    "MySQL error code 133: No record read before update"
    "MySQL error code 134: Record was already deleted (or record file crashed)"
    "MySQL error code 135: No more room in record file"
    "MySQL error code 136: No more room in index file"
    "MySQL error code 137: No more records (read after end of file)"
    "MySQL error code 138: Unsupported extension used for table"
    "MySQL error code 139: Too big row"
    "MySQL error code 140: Wrong create options"
    "MySQL error code 141: Duplicate unique key or constraint on write or update"
    "MySQL error code 142: Unknown character set used"
    "MySQL error code 143: Conflicting table definitions in sub-tables of MERGE table"
    "MySQL error code 144: Table is crashed and last repair failed"
    "MySQL error code 145: Table was marked as crashed and should be repaired"
    "MySQL error code 146: Lock timed out; Retry transaction"
    "MySQL error code 147: Lock table is full;  Restart program with a larger locktable"
    "MySQL error code 148: Updates are not allowed under a read only transactions"
    "MySQL error code 149: Lock deadlock; Retry transaction"
    "MySQL error code 150: Foreign key constraint is incorrectly formed"
    "MySQL error code 151: Cannot add a child row"
    "MySQL error code 152: Cannot delete a parent row"

[7906fcd85e9240429cceb0a64f361023.png]: /images/20220829/f7aa100bc37b439191e432c68aa75f33.png
[2ef32c1ce3654484b236af25368bdab1.png]: /images/20220829/ac89773517c94559b92cccc122d3b03b.png
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[0a6cf9231486414a8095f6dd113a2c7d.png]: /images/20220829/49189a49502e4aabba96e6975ce95083.png
[37e37dd76e0f42eb8e7c4c0bb3aab3cd.png]: /images/20220829/ac8c834f817248efb27847f755ff0153.png
[36d83bdde0524001a910df7a8c9c3083.png]: /images/20220829/e7ef93f79a6a4345ba87d3c272477bf3.png
[2a8ad08662864bc293b3c520e486c473.png]: /images/20220829/bae4c0fed8254989b5c8de9cc8bf825a.png
[325ec497200142f98be97ec17d2c9cf3.png]: /images/20220829/bc507b5188fa4eee9f508abe1b38b01b.png
[e8088a5b93c3426fbbdc4f28e7846553.png]: /images/20220829/2885d9f306914ee5b7eed8015bf0afb1.png
[477dc82c33be48e08841725c77a0c2b2.png]: /images/20220829/3fbc8f6b1ece4c92bbf4203af4c6d244.png
[4d6b63d257da4de185bb4abc117f07ee.png]: /images/20220829/bad8f8492cdd46979349ec16d038f05c.png