为什么我们在subprocess.Popen中使用stdout = PIPE？ [英] why should we use stdout=PIPE in subprocess.Popen?

问题描述

from subprocess import PIPE,Popen

p = Popen("ls -l",shell=True,stderr=PIPE,stdout=PIPE)
(out,err) = p.communicate()
print(out, err)

在上面的Popen调用中，如果我删除 stdout = PIPE ，我在每个列表后得到换行符 ls -l <​​/ code>输出。但是如果使用 stdout = PIPE ，我会显示 \\\
，而不是换行，如下

In above Popen call, if I remove stdout=PIPE, I am getting newline after every listing by ls -l in output. But if use stdout=PIPE, I get \n displayed, rather than newline, as below

b'total 67092\n-rw-r--r--  1 root root      171 May 27 09:08 new.py\n-rw-r--r--  1   
    root root       74 May 12 18:14 abcd.conf\n-rwxr-xr-x  1 root root     5948 May 13 13:21 abxyz.sh\ndrwxr-xr-x  2 root root     4096 May 13
12:39 log\ndrwxrwxrwx  3 root root     4096 May 14 16:02
newpy\n-rw-r--r--  1 root root      134 May 27 10:13
pipe.py\n-rw-r--r--  1 root root      155 May 27 10:07
proc.py\ndrwxrwxrwx  3 root root     4096 May 14 14:29 py\ndrwxr-xr-x
16 1000 1000\n' b''

$ b b

PIPE 如何在 subprocess.Popen 的情况下正常工作？为什么我们需要它？我得到适当的输出，而不使用它吗？

How does PIPE exactly works in case of subprocess.Popen? Why do we need it? I got proper output without using it also? Are we using this for getting both stderr, stdout?

推荐答案

删除 print（）调用看到的区别。

当你不把管道 ls 输出到Python，直接显示在您的终端上;它的输出到您的终端。如果你把它管道到Python，你会看到整个内容作为字节，包括换行字节（表示为 \\\
）。

When you do not pipe the ls output to Python, it is instead displayed on your terminal directly; it's output goes to your terminal. If you pipe it to Python, you get to see the whole contents as bytes, including newline bytes (represented as \n).

如果您希望以字面方式打印换行符，请解码结果：

Decode the results if you want the newlines to be printed literally:

print(out.decode('utf8'))

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