对于shell编程，其实特殊变量常用的有几个，重温下，算是一个小结吧。
1、位置变量：
$0 获取当前执行的shell脚本的文件名，包括路径。
$n 获取当前执行的shell脚本的第n个参数值，n=1..9，当n为0时，表示脚本的文件名，如果n大于9，用大括号括下来${10}
$* 获取当前shell的所有参数，将所有的命令行参数视为单个字符串，相当于”$1$2$3” ...注意与$#的区别
$# 获取当前shell命令行中参数的总个数
$@ 这个程序的所有参数”$1” “$2” “$3” “...”，这是将参数传递给其他程序的最佳方式，因为他会保留所有内嵌在每个参数里任何空白。
提示：$*和$@的区别？
2、进程状态变量
$$ 获取当前shell的进程号(PID)
$! 执行上一个指令的PID
$? 获取执行上一个指令的返回值（0为成功，非0为失败）#→这个变量很常用。
$_ 在此之前执行的命令或脚本的最后一个参数
注：以上有底色标记内容为生产场景中常用知识。
$ cat specVar.sh #!/bin/bash #Filename: specVar.sh #Email: watchsky126(at)hotmail.com #Version: v0.1 echo ‘$0 获取当前执行的shell脚本的文件名‘$0 echo ‘$n 获取当前执行的shell脚本的第n个参数值，n=1..9:‘‘$1‘=$1 ‘$2‘=$2 ‘$3‘=$3 echo‘$* 获取当前shell的所有参数"$1 $2 $3 ..."注意与$#的区别:‘$* echo ‘$# 获取当前shell命令行中参数的总个数:‘$# echo‘$$ 获取当前shell的进程号（PID）:‘$$ sleep2 & echo‘$! 执行上一个指令的PID:‘ $! echo‘$? 获取执行的上一个指令的返回值:‘ $? echo‘$@ 这个程序的所有参数 "$1" "$2""$3" "...":‘ $@ echo‘$_ 在此之前执行的命令或脚本的最后一个参数:‘$_ $ sh specVar.sh aa bb cc $0 获取当前执行的shell脚本的文件名specVar.sh $n 获取当前执行的shell脚本的第n个参数值，n=1..9:$1=aa $2=bb $3=cc $* 获取当前shell的所有参数"$1 $2 $3 ..."注意与$#的区别:aa bb cc $# 获取当前shell命令行中参数的总个数:3 $$ 获取当前shell的进程号（PID）:23699 $! 执行上一个指令的PID: 23700 $? 获取执行的上一个指令的返回值:0 $@ 这个程序的所有参数 "$1" "$2""$3" "...": aa bb cc $_ 在此之前执行的命令或脚本的最后一个参数:cc
Linux命令的返回值错误对照表
"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"
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原文地址：http://watchsky.blog.51cto.com/7550654/1626260
