[TOC]
问题
import commands as subprocess
status, _ = 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。
最新的Python32版本为3.5.3也就是将python3.5.3中的subprocess基本功能移植到了Python2中。但是subprocess32不包含原本commands中的函数。
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).stdout
def 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, data
def 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
subprocess.run()
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
