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shell脚本中$0 $1 $# $@ $* $? $$ 的各种符号意义详解
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shell脚本中$0 $1 $# $@ $* $? $$ 的各种符号意义详解
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发布时间: 2021-10-11
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## 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。 ![ ](https://img-blog.csdnimg.cn/2ef32c1ce3654484b236af25368bdab1.png) ![](https://img-blog.csdnimg.cn/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 | 名称 | 含义 | |--|:--| |$# |传给脚本的参数个数| |$0 |脚本本身的名字| |$1 |传递给该shell脚本的第一个参数| |$2 |传递给该shell脚本的第二个参数| |$@ |传给脚本的所有参数的列表| |$* |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| |$$ |脚本运行的当前进程ID号| |$? |显示最后命令的退出状态,0表示没有错误,其他表示有错误| ### 实例1 建立脚本peng.sh如下: ```bash #/bin/bash total=$[ $1 * $2 + $3 ] echo "$1 * $2 + $3=$total" ``` 运行如下: ```bash ./peng.sh 4 5 6 ``` 结果如下: ![ ](https://img-blog.csdnimg.cn/efcc46bc1fb845e898a37da989107ef9.png) ### 实例2 当把字符串输入给shell脚本的时候,注意是以空格作为分隔符,如果字符串本身就有空格的话,那么用双引号或者单引号,比如 ```bash #/bin/bash echo "$1 is pretty nice!" ``` 运行如下: ```bash ./peng.sh 一口Linux ``` 结果如下: ![ ](https://img-blog.csdnimg.cn/0a6cf9231486414a8095f6dd113a2c7d.png) ### 实例3 ```bash #!/bin/sh echo "参数个数:$#" echo "脚本名字:$0" echo "参数1:$1" echo "参数2:$2" echo "所有参数列表:$@" echo "pid:$$" 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: ![](https://img-blog.csdnimg.cn/37e37dd76e0f42eb8e7c4c0bb3aab3cd.png) ### 实例4 使用for循环进行参数遍历 示例: ```bash #!/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 ``` ![ ](https://img-blog.csdnimg.cn/36d83bdde0524001a910df7a8c9c3083.png) ![ ](https://img-blog.csdnimg.cn/2a8ad08662864bc293b3c520e486c473.png) ### 实例5 小技巧1:在"$*"和$*中遍历参数的区别 示例: ```bash #!/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 $i done ``` ![ ](https://img-blog.csdnimg.cn/325ec497200142f98be97ec17d2c9cf3.png) ## 三、linux命令执行返回值**$?**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: ![ ](https://img-blog.csdnimg.cn/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: ![ ](https://img-blog.csdnimg.cn/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}"` ```bash root@ubuntu:/home/peng/zhh# export PS1="[\$?]${PS1}" [0]root@ubuntu:/home/peng/zhh# ls ``` ![ ](https://img-blog.csdnimg.cn/4d6b63d257da4de185bb4abc117f07ee.png) `export PS1="[\$?]${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: ```bash $ 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: ```bash "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: Ex
ec 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 ex
ec 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" ```
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