技术笔记:Linux命令的返回值

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简介: 技术笔记:Linux命令的返回值

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 )。


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:


$ ls *.png


Diagram1.png eqn.png peazip.png


eqn4.png Mandelbrot.png x2.png


$ echo $?


0


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。我们可以试着 ls 一个不存在的文件:


$ ls linuxgem


ls: 无法访问 linuxgem: 没有那个文件或目录


$ echo $?


2


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:


$ export PS1="【\$?】${PS1}"


【0】test@test:$


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~


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:


$ 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~


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 //代码效果参考:http://www.jhylw.com.cn/112226483.html

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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