python中os.system()的返回值

1、python中的 os.system(cmd)的返回值与linux命令返回值(具体参见本文附加内容)的关系

你们都习惯用os.systemv()函数执行linux命令,该函数的返回值十进制数(分别对应一个16位的二进制数)。该函数的返回值与 linux命令返回值二者的转换关系为:该函数的返回值(十进制)转化成16二进制数,截取其高八位(若是低位数是0的状况下,有关操做系统的错误码共 131个,因此低位都是零),而后转乘十进制数即为 linux命令返回值0。node

例如:python

os.system()返回值为0 linux命令返回值也为0.linux

os.system()返回值为256,十六位二进制数示为:00000001,00000000,高八位转乘十进制为 1 对应linux命令返回值 1web

os.system()返回值为512,十六位二进制数示为:00000010,00000000,高八位转乘十进制为 2 对应 linux命令返回值 2app

…其它同理…dom

os.system()返回值为32512,十六位二进制数示为:01111111,00000000,高八位转乘十进制为 127 对应 linux命令返回值 127socket

问题:/bin/xxx.py是一个返回码为1的程序。当python 程序使用os.system(”./bin/xxx.py”) 这样调用的时候, 成功运行后os.system 的返回值出现了问题,变成了256 ,也就是0×100。而不是正常应该返回的1。ide

解决:查阅了文档发现os.system()的返回为:svg

On Unix, the return value is the exit status of the process encoded in the format specified for wait().

而os.wait()的返回为:函数

a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number is zero);

os.system的返回值并非执行程序的返回结果。而是一个16位的数,它的高位才是返回码。也就是说os.system()返回256即0×0100,返回码应该是其高位0×01即1。因此要获取程序运行退出的值(好比C的main函数中的return 0),须要处理一下。

ret = os.system('./a.out')

ret >>= 8

这样才能获取到正确的返回值。另外还要注意:python获取到的值是无符号整数,因此返回负值的时候,打印出来是很大的正值。好比返回-1,python 会获取到255, -2则254,以此类推。

因此最好就判断是否为0就能够了,实在要判断本身写的c程序返回值,建议返回0,1,2,3等值,出错返回-1。

另外,我遇到一次明明处理好了返回值,c程序调试信息提示也该返回值0了,结果python获取到的是 -1,并且不管c程序返回多少,python都获取-1。后来排查c程序的问题,发现原来是由于我这个python程序自己是由另外一个C程序调用的,而调 用它的那个C程序中将SIGCLD信号忽略了(这代表python是根据子进程退出时产生的信号来获取返回值的),我将那个C程序的SIGCLD绑定到函 数,即便那个函数什么也不作,python也能获取到正确的返回值了。

2、 linux命令执行后不管成功与否都有一个返回值:

若是为 0,则表示命令执行成功,其它值则表示错误,具体的错误码含义以下:

"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"