如何解释 Python commands.getstatusoutput() 中的状态代码
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原文地址: http://stackoverflow.com/questions/1535672/
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How to interpret status code in Python commands.getstatusoutput()
提问by Schof
In a related question, I asked where to find the documentation for the C function "wait." This was an attempt to figure out return codes for the commands.getstatusoutput() module. Stackoverflow came through, but the documentation didn't help. Here's what puzzles me:
在一个相关的问题中，我问到哪里可以找到 C 函数“wait”的文档。这是试图找出 commands.getstatusoutput() 模块的返回代码。Stackoverflow 通过了，但文档没有帮助。这是让我困惑的地方：
#!/usr/bin/python
import commands
goodcommand = 'ls /'
badcommand = 'ls /fail'
status, output = commands.getstatusoutput(goodcommand)
print('Good command reported status of %s' % status)
status, output = commands.getstatusoutput(badcommand)
print('Bad command reported status of %s' % status)
When run on OS X (Leopard) I get the following output: (Which matches the documentation.)
在 OS X (Leopard) 上运行时，我得到以下输出：（与文档匹配。）
$ python waitest.py
Good command reported status of 0
Bad command reported status of 256
On OS X, doing an "ls /fail ; echo $?" gets the following output:
在 OS X 上，执行“ls /fail ; echo $?” 得到以下输出：
$ ls /fail ; echo $?
ls: /fail: No such file or directory
1
When run on Linux (Ubuntu Hardy) I get the following output:
在 Linux (Ubuntu Hardy) 上运行时，我得到以下输出：
$ python waitest.py
Good command reported status of 0
Bad command reported status of 512
On Ubuntu, doing "ls /fail" gets a 2:
在 Ubuntu 上，执行 "ls /fail" 会得到 2：
$ ls /fail ; echo $?
ls: cannot access /fail: No such file or directory
2
So Python appears to be multiplying status codes by 256. Huh? Is this documented somewhere?
所以 Python 似乎是将状态代码乘以 256。嗯？这是在某处记录的吗？
回答by abbot
There is a set of functions in osmodule (os.WIFCONTINUED, os.WIFSTOPPED, os.WTERMSIG, os.WCOREDUMP, os.WIFEXITED, os.WEXITSTATUS, os.WIFSIGNALED, os.WSTOPSIG), which correspond to macros from wait(2)manual. You should use them to interpret the status code.
os模块 ( os.WIFCONTINUED, os.WIFSTOPPED, os.WTERMSIG, os.WCOREDUMP, os.WIFEXITED, os.WEXITSTATUS, os.WIFSIGNALED, os.WSTOPSIG) 中有一组函数，它们对应于wait(2)手册中的宏。您应该使用它们来解释状态代码。
For example, to get the exit code you should use os.WEXITSTATUS(status)
例如，要获取您应该使用的退出代码 os.WEXITSTATUS(status)
A better idea would be to switch to subprocessmodule.
一个更好的主意是切换到subprocess模块。
回答by Schof
Wow. The insight that it was multiplying by 256 got me there. Searching for "python commands +256" got me to a Python Module Of The Weekarticle which explains what's going on.
哇。它乘以 256 的洞察力让我到达了那里。搜索“python 命令 +256”让我看到了一篇Python Module Of The Week文章，它解释了正在发生的事情。
Here's a snippet from that page:
这是该页面的一个片段：
The function getstatusoutput() runs a command via the shell and returns the exit code and the text output (stdout and stderr combined). The exit codes are the same as for the C function wait() or os.wait(). The code is a 16-bit number. The low byte contains the signal number that killed the process. When the signal is zero, the high byte is the exit status of the program. If a core file was produced, the high bit of the low byte is set.
函数 getstatusoutput() 通过 shell 运行命令并返回退出代码和文本输出（stdout 和 stderr 组合）。退出代码与 C 函数 wait() 或 os.wait() 相同。该代码是一个 16 位数字。低字节包含杀死进程的信号编号。当信号为零时，高字节为程序退出状态。如果生成了核心文件，则设置低字节的高位。
And some of Doug's code:
还有一些道格的代码：
from commands import *
def run_command(cmd):
print 'Running: "%s"' % cmd
status, text = getstatusoutput(cmd)
exit_code = status >> 8
signal_num = status % 256
print 'Signal: %d' % signal_num
print 'Exit : %d' % exit_code
print 'Core? : %s' % bool(exit_code / 256)
print 'Output:'
print text
print
run_command('ls -l *.py')
run_command('ls -l *.notthere')
run_command('echo "WAITING TO BE KILLED"; read input')
回答by Mark Rushakoff
Looking at commands.py:
看着commands.py：
def getstatusoutput(cmd):
"""Return (status, output) of executing cmd in a shell."""
import os
pipe = os.popen('{ ' + cmd + '; } 2>&1', 'r')
text = pipe.read()
sts = pipe.close()
if sts is None: sts = 0
if text[-1:] == '\n': text = text[:-1]
return sts, text
We see stsholds the value of os.popen(...).close(). Looking at thatdocumentation, os.popen(...).close()returns the value of os.wait:
我们看到sts持有 的价值os.popen(...).close()。查看该文档，os.popen(...).close()返回以下值os.wait：
os.wait()Wait for completion of a child process, and return a tuple containing its pid and exit status indication: 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); the high bit of the low byte is set if a core file was produced. Availability: Unix.
os.wait()等待子进程完成，并返回一个包含其pid和退出状态指示的元组：一个16位的数字，低字节是杀死进程的信号号，高字节是退出状态（如果信号数字为零）；如果生成了核心文件，则设置低字节的高位。可用性：Unix。
Emphasis was mine. I agree that this "encoding" isn't terribly intuitive, but at least it was fairly obvious at a glance that it was being multiplied/bit-shifted.
重点是我的。我同意这种“编码”不是非常直观，但至少它被乘法/位移一目了然。
回答by Felix Labrecque
I think the code detection is incorrect.
我认为代码检测不正确。
"If a core file was produced, the high bit of the low byte is set." means 128.
“如果生成了核心文件，则设置低字节的高位。” 表示 128。
so I think the core line should be
所以我认为核心线应该是
print 'Core? : %s' % bool(status & 128)
