Python 子进程:使用 subprocess.run 链接命令 [英] Python subprocess: chaining commands with subprocess.run

问题描述

我正在 Python 中试验 subprocess.run3.5.将两个命令链接在一起，我认为以下应该有效:

I'm experimenting with subprocess.run in Python 3.5. To chain two commands together, I would have thought that the following should work:

import subprocess

ps1 = subprocess.run(['ls'], universal_newlines=True, stdout=subprocess.PIPE)
ps2 = subprocess.run(['cowsay'], stdin=ps1.stdout)

然而，这失败了:

AttributeError: 'str' object has no attribute 'fileno'

ps2 需要一个类似文件的对象，但 ps1 的输出是一个简单的字符串.

ps2 was expecting a file-like object, but the output of ps1 is a simple string.

有没有办法将命令与 subprocess.run 链接在一起?

Is there a way to chain commands together with subprocess.run?

推荐答案

subprocess.run() 不能用于实现 ls |cowsay 没有外壳，因为它不允许同时运行单个命令:每个 subprocess.run() 调用等待进程完成，这就是它返回 CompletedProcess 的原因 对象(注意那里的已完成"一词).ps1.stdout 在您的代码中是一个字符串，这就是为什么您必须将其作为 input 而不是期望文件的 stdin 参数传递的原因/管道(有效 .fileno()).

subprocess.run() can't be used to implement ls | cowsay without the shell because it doesn't allow to run the individual commands concurrently: each subprocess.run() call waits for the process to finish that is why it returns CompletedProcess object (notice the word "completed" there). ps1.stdout in your code is a string that is why you have to pass it as input and not the stdin parameter that expects a file/pipe (valid .fileno()).

要么使用shell:

subprocess.run('ls | cowsay', shell=True)

或者使用subprocess.Popen，并发运行子进程:

Or use subprocess.Popen, to run the child processes concurrently:

from subprocess import Popen, PIPE

cowsay = Popen('cowsay', stdin=PIPE)
ls = Popen('ls', stdout=cowsay.stdin)
cowsay.communicate()
ls.wait()

请参阅如何使用 subprocess.Popen 通过管道连接多个进程?

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