python Popen shell=真实行为 [英] python Popen shell=True behavior

问题描述

为什么这不起作用:subprocess.Popen(["ls -l | grep myfile"], shell=False)但这一行有效: subprocess.Popen(["ls -l | grep myfile"], shell=True)我理解这个 shell=True 在内部创建一个子 shell 并执行命令.但不明白这如何影响 Popen 行为

Why would this doesn't work: subprocess.Popen(["ls -l | grep myfile"], shell=False) But this line works: subprocess.Popen(["ls -l | grep myfile"], shell=True) I understand this shell=True create a sub shell internally and execute command. But didn't understand how this affect Popen behavior

推荐答案

Popen() 使用 subprocess 模块内的代码进行子流程管理.它不知道使用 | 进行管道传输，也不知道您传递的字符串是程序还是参数，就像在您使用 ls 的示例中一样，它会假设除 ls 本身之外的所有其他内容都是程序的参数.它将尝试执行列表中的第一项并将所有其他项作为参数传递.

Popen() does the subprocess management with the code inside the subprocess module. It doesn't know about piping with |, and it doesn't know whether the string you pass is a program or an argument, like in your example with ls it will assume that everything else except ls itself is arguments for the program. It will try to execute the first item in list and pass all other items as arguments.

当您使用 shell=True 时，您可能会认为它(例如在 UNIX 上)运行 /bin/sh -c 并使用您作为字符串提供的 arglist.所以

When you use shell=True, you may think of it (e.g. on UNIX) as running /bin/sh -c with arglist you provided as a string. So

Popen('ls -l | grep myfile', shell=True)

接近于

Popen(['/bin/sh', '-c', 'ls -l | grep myfile'])

在这两种情况下，参数处理实际上是由您的 shell 完成的.

In both cases, argument handling is actually done by your shell.

对于管道和 shell=False，您应该使用 subprocess.PIPE 和 stdout/stdin/stderr 重定向以及 subprocess 模块中提供的工具.

For piping and shell=False, you should use subprocess.PIPE and stdout/stdin/stderr redirections with the tools provided in subprocess module.

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