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linux $?的含义

分类： LINUX

2015-06-18 20:06:23

linux $?的含义
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：

  1. $ ls *.png
  2. Diagram1.png eqn.png peazip.png
  3. eqn4.png Mandelbrot.png x2.png
  4. $ echo $?
  5. 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：
  1. $ ls linuxgem
  2. ls: 无法访问 linuxgem: 没有那个文件或目录
  3. $ echo $?
  4. 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：
  1. galeki@localhost ~ $ export PS1="[\$?]${PS1}"
  2. [0]galeki@localhost ~ $
  3. 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：
  1. $ perror 2
  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：
  1. "OS error code 1: Operation not permitted"
  2. "OS error code 2: No such file or directory"
  3. "OS error code 3: No such process"
  4. "OS error code 4: Interrupted system call"
  5. "OS error code 5: Input/output error"
  6. "OS error code 6: No such device or address"
  7. "OS error code 7: Argument list too long"
  8. "OS error code 8: Exec format error"
  9. "OS error code 9: Bad file descriptor"
  10. "OS error code 10: No child processes"
  11. "OS error code 11: Resource temporarily unavailable"
  12. "OS error code 12: Cannot allocate memory"
  13. "OS error code 13: Permission denied"
  14. "OS error code 14: Bad address"
  15. "OS error code 15: Block device required"
  16. "OS error code 16: Device or resource busy"
  17. "OS error code 17: File exists"
  18. "OS error code 18: Invalid cross-device link"
  19. "OS error code 19: No such device"
  20. "OS error code 20: Not a directory"
  21. "OS error code 21: Is a directory"
  22. "OS error code 22: Invalid argument"
  23. "OS error code 23: Too many open files in system"
  24. "OS error code 24: Too many open files"
  25. "OS error code 25: Inappropriate ioctl for device"
  26. "OS error code 26: Text file busy"
  27. "OS error code 27: File too large"
  28. "OS error code 28: No space left on device"
  29. "OS error code 29: Illegal seek"
  30. "OS error code 30: Read-only file system"
  31. "OS error code 31: Too many links"
  32. "OS error code 32: Broken pipe"
  33. "OS error code 33: Numerical argument out of domain"
  34. "OS error code 34: Numerical result out of range"
  35. "OS error code 35: Resource deadlock avoided"
  36. "OS error code 36: File name too long"
  37. "OS error code 37: No locks available"
  38. "OS error code 38: Function not implemented"
  39. "OS error code 39: Directory not empty"
  40. "OS error code 40: Too many levels of symbolic links"
  41. "OS error code 42: No message of desired type"
  42. "OS error code 43: Identifier removed"
  43. "OS error code 44: Channel number out of range"
  44. "OS error code 45: Level 2 not synchronized"
  45. "OS error code 46: Level 3 halted"
  46. "OS error code 47: Level 3 reset"
  47. "OS error code 48: Link number out of range"
  48. "OS error code 49: Protocol driver not attached"
  49. "OS error code 50: No CSI structure available"
  50. "OS error code 51: Level 2 halted"
  51. "OS error code 52: Invalid exchange"
  52. "OS error code 53: Invalid request descriptor"
  53. "OS error code 54: Exchange full"
  54. "OS error code 55: No anode"
  55. "OS error code 56: Invalid request code"
  56. "OS error code 57: Invalid slot"
  57. "OS error code 59: Bad font file format"
  58. "OS error code 60: Device not a stream"
  59. "OS error code 61: No data available"
  60. "OS error code 62: Timer expired"
  61. "OS error code 63: Out of streams resources"
  62. "OS error code 64: Machine is not on the network"
  63. "OS error code 65: Package not installed"
  64. "OS error code 66: Object is remote"
  65. "OS error code 67: Link has been severed"
  66. "OS error code 68: Advertise error"
  67. "OS error code 69: Srmount error"
  68. "OS error code 70: Communication error on send"
  69. "OS error code 71: Protocol error"
  70. "OS error code 72: Multihop attempted"
  71. "OS error code 73: RFS specific error"
  72. "OS error code 74: Bad message"
  73. "OS error code 75: Value too large for defined data type"
  74. "OS error code 76: Name not unique on network"
  75. "OS error code 77: File descriptor in bad state"
  76. "OS error code 78: Remote address changed"
  77. "OS error code 79: Can not access a needed shared library"
  78. "OS error code 80: Accessing a corrupted shared library"
  79. "OS error code 81: .lib section in a.out corrupted"
  80. "OS error code 82: Attempting to link in too many shared libraries"
  81. "OS error code 83: Cannot exec a shared library directly"
  82. "OS error code 84: Invalid or incomplete multibyte or wide character"
  83. "OS error code 85: Interrupted system call should be restarted"
  84. "OS error code 86: Streams pipe error"
  85. "OS error code 87: Too many users"
  86. "OS error code 88: Socket operation on non-socket"
  87. "OS error code 89: Destination address required"
  88. "OS error code 90: Message too long"
  89. "OS error code 91: Protocol wrong type for socket"
  90. "OS error code 92: Protocol not available"
  91. "OS error code 93: Protocol not supported"
  92. "OS error code 94: Socket type not supported"
  93. "OS error code 95: Operation not supported"
  94. "OS error code 96: Protocol family not supported"
  95. "OS error code 97: Address family not supported by protocol"
  96. "OS error code 98: Address already in use"
  97. "OS error code 99: Cannot assign requested address"
  98. "OS error code 100: Network is down"
  99. "OS error code 101: Network is unreachable"
  100. "OS error code 102: Network dropped connection on reset"
  101. "OS error code 103: Software caused connection abort"
  102. "OS error code 104: Connection reset by peer"
  103. "OS error code 105: No buffer space available"
  104. "OS error code 106: Transport endpoint is already connected"
  105. "OS error code 107: Transport endpoint is not connected"
  106. "OS error code 108: Cannot send after transport endpoint shutdown"
  107. "OS error code 109: Too many references: cannot splice"
  108. "OS error code 110: Connection timed out"
  109. "OS error code 111: Connection refused"
  110. "OS error code 112: Host is down"
  111. "OS error code 113: No route to host"
  112. "OS error code 114: Operation already in progress"
  113. "OS error code 115: Operation now in progress"
  114. "OS error code 116: Stale NFS file handle"
  115. "OS error code 117: Structure needs cleaning"
  116. "OS error code 118: Not a XENIX named type file"
  117. "OS error code 119: No XENIX semaphores available"
  118. "OS error code 120: Is a named type file"
  119. "OS error code 121: Remote I/O error"
  120. "OS error code 122: Disk quota exceeded"
  121. "OS error code 123: No medium found"
  122. "OS error code 124: Wrong medium type"
  123. "OS error code 125: Operation canceled"
  124. "OS error code 126: Required key not available"
  125. "OS error code 127: Key has expired"
  126. "OS error code 128: Key has been revoked"
  127. "OS error code 129: Key was rejected by service"
  128. "OS error code 130: Owner died"
  129. "OS error code 131: State not recoverable"
  130. "MySQL error code 132: Old database file"
  131. "MySQL error code 133: No record read before update"
  132. "MySQL error code 134: Record was already deleted (or record file crashed)"
  133. "MySQL error code 135: No more room in record file"
  134. "MySQL error code 136: No more room in index file"
  135. "MySQL error code 137: No more records (read after end of file)"
  136. "MySQL error code 138: Unsupported extension used for table"
  137. "MySQL error code 139: Too big row"
  138. "MySQL error code 140: Wrong create options"
  139. "MySQL error code 141: Duplicate unique key or constraint on write or update"
  140. "MySQL error code 142: Unknown character set used"
  141. "MySQL error code 143: Conflicting table definitions in sub-tables of MERGE table"
  142. "MySQL error code 144: Table is crashed and last repair failed"
  143. "MySQL error code 145: Table was marked as crashed and should be repaired"
  144. "MySQL error code 146: Lock timed out; Retry transaction"
  145. "MySQL error code 147: Lock table is full; Restart program with a larger locktable"
  146. "MySQL error code 148: Updates are not allowed under a read only transactions"
  147. "MySQL error code 149: Lock deadlock; Retry transaction"
  148. "MySQL error code 150: Foreign key constraint is incorrectly formed"
  149. "MySQL error code 151: Cannot add a child row"
  150. "MySQL error code 152: Cannot delete a parent row"


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