linux下命令列執行後的傳回值-錯誤值__linux

我們最開始學習的C語言中，主函數中int main()函數的最後總會加一個return 0;充當傳回值，當初我們並不知道這個傳回值的意義是什麼，我們經常使用的是普通函數中的傳回值，當函數執行一個任務時，函數執行完畢之後總會返回一個適當的值來告訴執行者該函數執行的情況

Linux 下，在terminal下，控制台下運行命令，所有的命令在結束時，都會返回一個數字值，這個值即為傳回值，每個傳回值都對應著一個錯誤號碼，根據錯誤號碼我們可以大致推斷這個函數執行的情況。另外在terminal下，有一個特殊的環境變數 $?，儲存著前一個程式的傳回值，我們可以試試：

[root@oldpan ~]# lslnmp1.4  lnmp1.4.tar.gz  lnmp-install.log[root@oldpan ~]# echo $?0

上面通過echo觀察執行ls的傳回值，發現是0，說明該命令執行成功，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。我們可以試著 ls 一個不存在的檔案：

[root@oldpan ~]# ls aaals: cannot access aaa: No such file or directory[root@oldpan ~]# echo o $?o 2

顯然這裡的傳回值發生了變化，變為2，意味著上面的命令執行有問題。

如果覺得每次都需要 echo $? 比較麻煩我們可以將其放到提示符中：

[root@oldpan ~]# export PS1="[\$?]${PS1}"[0][root@oldpan ~]# ls aaals: cannot access aaa: No such file or directory[2][root@oldpan ~]#    

通過上面的命令可以再提示符的最前面看到上一次執行命令的傳回值結果。
另外，我們可以通過perror 這個命令來查看錯誤的資訊：

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

錯誤對照表：

"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"