Python - 如何使用管道执行shell命令，但没有'shell = True'?

问题描述

我有一个案例想在 Python 中执行下面的 shell 命令并得到输出，

I have a case to want to execute the following shell command in Python and get the output,

echo This_is_a_testing | grep -c test

我可以使用这个python代码在python中执行上面的shell命令，

I could use this python code to execute the above shell command in python,

>>> import subprocess
>>> subprocess.check_output("echo This_is_a_testing | grep -c test", shell=True)
'1
'

但是，由于我不想使用shell=True"；选项，我尝试了下面的python代码，

However, as I do not want to use the "shell=True" option, I tried the following python code,

>>> import subprocess
>>> p1 = subprocess.Popen(["echo", "This_is_a_testing"], stdout=subprocess.PIPE)
>>> p2 = subprocess.Popen(["grep", "-c", "test"], stdin=p1.stdout)
>>> p1.stdout.close()
>>> p2.communicate()
(None, None)

我想知道为什么输出是无"?正如我在网页中提到的描述:http://docs.python.org/library/subprocess.html#subprocess.PIPE

I wonder why the output is "None" as I have referred to the descriptions in the webpage : http://docs.python.org/library/subprocess.html#subprocess.PIPE

我是否遗漏了代码中的一些要点?有什么建议/想法吗?提前致谢.

Had I missed some points in my code ? Any suggestion / idea ? Thanks in advance.

推荐答案

来自手册:

要在结果元组中获得除 None 以外的任何内容，您需要给出stdout=PIPE 和/或 stderr=PIPE

to get anything other than None in the result tuple, you need to give stdout=PIPE and/or stderr=PIPE

p2 = subprocess.Popen(["grep", "-c", "test"], stdin=p1.stdout, stdout=subprocess.PIPE)

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