shell指令碼中$0 $1 $# $@ $* $? $$ 的各種符號意義詳解
阿新 • • 發佈：2021-10-09
一、概述
shell中有兩類字元：普通字元、元字元。
1. 普通字元
在Shell中除了本身的字面意思外沒有其他特殊意義，即普通純文字；
2. 元字元
是Shell的保留字元，在Shell中有著特殊的含義。
今天主要介紹一下shell中字元$的各種用法。
二、轉義字元$
在linux shell指令碼中經常用到字元$，下面是$的一些常見用法
| 名稱 | 含義 |
|---|---|
| $# | 傳給指令碼的引數個數 |
| $0 | 指令碼本身的名字 |
| $1 | 傳遞給該shell指令碼的第一個引數 |
| $2 | 傳遞給該shell指令碼的第二個引數 |
| $@ | 傳給指令碼的所有引數的列表 |
| $* | 以一個單字串顯示所有向指令碼傳遞的引數，與位置變數不同，引數可超過9個 |
| $$ | 指令碼執行的當前程序ID號 |
| $? | 顯示最後命令的退出狀態，0表示沒有錯誤，其他表示有錯誤 |
例項1
建立指令碼peng.sh如下：
#/bin/bash
total=$[ $1 * $2 + $3 ]
echo "$1 * $2 + $3 = $total"
執行如下：
./peng.sh 4 5 6
結果如下：
例項2
當把字串輸入給shell指令碼的時候，注意是以空格作為分隔符，如果字串本身就有空格的話，那麼用雙引號或者單引號，比如
#/bin/bash
echo "$1 is pretty nice!"
執行如下：
./peng.sh 一口Linux
結果如下：
例項3
#!/bin/sh
echo "引數個數:$#"
echo "指令碼名字:$0"
echo "引數1:$1"
echo "引數2:$2"
echo "所有引數列表:$@"
echo "pid:$$"
if [ $1 = 100 ]
then
echo "命令退出狀態：$?"
exit 0 #引數正確，退出狀態為0
else
echo "命令退出狀態：$?"
exit 1 #引數錯誤，退出狀態1
fi
執行結果：
例項4
使用for迴圈進行引數遍歷
示例：
#!/bin/bash number=65 #定義一個退出值 index=1 #定義一個計數器 if [ -z "$1" ];then #對使用者輸入的引數做判斷，如果未輸入引數則返回指令碼的用法並退出，退出值65 echo "Usage:$0 + 引數" exit $number fi echo "listing args with \$*:" #在螢幕輸入，在$*中遍歷引數 for arg in $* do echo "arg: $index = $arg" let index+=1 done echo index=1 #將計數器重新設定為1 echo "listing args with \"\$@\":" #在"$@"中遍歷引數 for arg in "$@" do echo "arg: $index = $arg" let index+=1 done
例項5
小技巧1：在"$"和$中遍歷引數的區別
示例：
#!/bin/bash
number=11
if [ $# -eq 0 ];then
echo "Usage: $0 + 引數"
exit $number
fi
for i in $* #在$*中遍歷引數，此時每個引數都是獨立的，會遍歷$#次
do
echo $i
done
echo
for i in "$*" #在"$*"中遍歷引數，此時"$*"被擴充套件為包含所有位置引數的單個字串，只遍歷一次
do
echo $i
done
三、linux命令執行返回值$?說明
在 Linux 下，不管你是啟動一個桌面程式也好，還是在控制檯下執行命令，所有的程式在結束時，都會返回一個數字值，這個值叫做返回值，或者稱為錯誤號 ( Error Number )。
1. 在控制檯下，有一個特殊的環境變數 $?，儲存著前一個程式的返回值，我們可以試試：
先隨便執行個命令，比如像上面的 ls 某些檔案，然後通過 echo $?，列印 $? 的值～
我們發現返回值是 0，這是什麼意思呢？
只要返回值是 0，就代表程式執行成功了～
也就是說，如果 $? 變數的值不是 0 的話，就表示上一個命令在執行的過程中出錯了。
2. 我們可以試著 ls 一個不存在的檔案：
這樣，對於某些打印出一堆不熟悉的英文資訊的命令，可以方便的看出它是否成功執行結束。
不過，每次都 echo $? 一下太累了，沒關係，你可以把 $? 放在提示符裡去：
3. 將上次命令執行是否成功的返回值放到提示符裡面去：export PS1="[\$?]${PS1}"
root@ubuntu:/home/peng/zhh# export PS1="[\$?]${PS1}"
[0]root@ubuntu:/home/peng/zhh# ls
export PS1="[\$?]${PS1}" 這個命令把 $? 的值放在的提示符的最前面，這樣每次執行完命令，這個值都會自動更新，這下就一目瞭然了～
4. 用perror檢視錯誤提示
那麼如果返回的值不是 0，我們要怎麼知道是那裡出錯了呢？
大多數的程式出錯都會給出提示，如果沒有提示的話，可以用 perror 這個程式來檢視錯誤的資訊，比如返回值是 2，我們可以執行下面命令：
$ perror 2
OS error code 2: No such file or directory
這樣就清楚了，原來是檔案不存在～
該命令需要安裝
apt-get install perror
5. 給出錯誤程式碼及其具體原因對照表：
"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"