[TOC]

问题

import commands as subprocessstatus, _ = subprocess.getstatusoutput("ps -elf|grep fuckU")# status:# 255

• 这里的status按照grep的定义其实应该返回1，也就是没有grep到匹配项，在shell中echo $? 结果为1

  但是python2的getstatusoutput获取的并不是os.exitcode()而是os.wait()的返回值。

• python3由于使用的是subprocess = modified(commands + subprocess)，同样执行

  status, _ = subprocess.getstatusoutput("ps -elf|grep fuckU")

  得到的status为正确的1

我是怎么解决这个问题

兼顾Python2和Python3的使用习惯，使用google开源的subprocess32代替commands

什么是subprocess32

谷歌将Python32的subprocess移植到了python2版本中。据说这是线程安全的版本。

Timeout support backported from Python 3.3 is included.The run() API from Python 3.5 was backported in subprocess32 3.5.0.Otherwise features are frozen at the 3.2 level.

这里我们使用subprocess32.run()方法去模拟getstatusoutput等便捷的函数(python3官方实现)

# 原本的timeout=None，因为Python2不支持*args,**kwargs外再有kwargs，暂时移出参数项，放至函数体内# def check_output(*popenargs, timeout=None, **kwargs):def check_output(*popenargs, **kwargs):    r"""Run command with arguments and return its output.    If the exit code was non-zero it raises a CalledProcessError.  The    CalledProcessError object will have the return code in the returncode    attribute and output in the output attribute.    The arguments are the same as for the Popen constructor.  Example:    >>> check_output(["ls", "-l", "/dev/null"])    b'crw-rw-rw- 1 root root 1, 3 Oct 18  2007 /dev/null\n'    The stdout argument is not allowed as it is used internally.    To capture standard error in the result, use stderr=STDOUT.    >>> check_output(["/bin/sh", "-c",    ...               "ls -l non_existent_file ; exit 0"],    ...              stderr=STDOUT)    b'ls: non_existent_file: No such file or directory\n'    There is an additional optional argument, "input", allowing you to    pass a string to the subprocess's stdin.  If you use this argument    you may not also use the Popen constructor's "stdin" argument, as    it too will be used internally.  Example:    >>> check_output(["sed", "-e", "s/foo/bar/"],    ...              input=b"when in the course of fooman events\n")    b'when in the course of barman events\n'    If universal_newlines=True is passed, the "input" argument must be a    string and the return value will be a string rather than bytes.    """    timeout = None    if 'stdout' in kwargs:        raise ValueError('stdout argument not allowed, it will be overridden.')    if 'input' in kwargs and kwargs['input'] is None:        # Explicitly passing input=None was previously equivalent to passing an        # empty string. That is maintained here for backwards compatibility.        kwargs['input'] = '' if kwargs.get('universal_newlines', False) else b''    return subprocess.run(*popenargs, stdout=subprocess.PIPE, timeout=timeout, check=True,                          **kwargs).stdoutdef getstatusoutput(cmd):    """Return (exitcode, output) of executing cmd in a shell.    Execute the string 'cmd' in a shell with 'check_output' and    return a 2-tuple (status, output). The locale encoding is used    to decode the output and process newlines.    A trailing newline is stripped from the output.    The exit status for the command can be interpreted    according to the rules for the function 'wait'. Example:    >>> import subprocess    >>> subprocess.getstatusoutput('ls /bin/ls')    (0, '/bin/ls')    >>> subprocess.getstatusoutput('cat /bin/junk')    (1, 'cat: /bin/junk: No such file or directory')    >>> subprocess.getstatusoutput('/bin/junk')    (127, 'sh: /bin/junk: not found')    >>> subprocess.getstatusoutput('/bin/kill $$')    (-15, '')    """    try:        data = check_output(cmd, shell=True, universal_newlines=True, stderr=subprocess.STDOUT)        exitcode = 0    except subprocess.CalledProcessError as ex:        data = ex.output        exitcode = ex.returncode    if data[-1:] == '\n':        data = data[:-1]    return exitcode, datadef getoutput(cmd):    """Return output (stdout or stderr) of executing cmd in a shell.    Like getstatusoutput(), except the exit status is ignored and the return    value is a string containing the command's output.  Example:    >>> import subprocess    >>> subprocess.getoutput('ls /bin/ls')    '/bin/ls'    """    return getstatusoutput(cmd)[1]

题外话

其实python官方推荐使用这个函数执行系统命令

但是这个函数将输出直接print到终端中

如果需要屏蔽恣意的屏幕输出，可以使用subprocess.DEVNULL (subprocess 3.5.3中有)

# 即x = subprocess.run('echo 250', shell=True, stderr=subprocess.DEVNULL, stdout=subprocess.DEVNULL)# x:# CompletedProcess(args='echo 250', returncode=0)# reference: https://stackoverflow.com/questions/8529390/is-there-a-quiet-version-of-subprocess-call