Python:执行 shell 命令

问题描述

我需要这样做:

paste file1 file2 file3 > result

我的 python 脚本中有以下内容:

I have the following in my python script:

from subprocess import call

// other code here.

// Here is how I call the shell command

call ["paste", "file1", "file2", "file3", ">", "result"])

很遗憾，我收到了这个错误:

Unfortunately I get this error:

paste: >: 没有这样的文件或目录.

对此的任何帮助都会很棒！

Any help with this will be great!

推荐答案

有两种方法.

1. 使用 shell=True:

call("paste file1 file2 file3 >result", shell=True)

重定向，>，是一个shell特性.因此，您只能在使用 shell 时访问它:shell=True.

Redirection, >, is a shell feature. Consequently, you can only access it when using a shell: shell=True.

保持shell=False，使用python进行重定向:

Keep shell=False and use python to perform the redirection:

with open('results', 'w') as f:
    subprocess.call(["paste", "file1", "file2", "file3"], stdout=f)

第二个通常是首选，因为它避免了 shell 的变幻莫测.

The second is normally preferred as it avoids the vagaries of the shell.

不使用 shell 时，> 只是命令行上的另一个字符.因此，请考虑错误消息:

When the shell is not used, > is just another character on the command line. Thus, consider the error message:

paste: >: No such file or directory. 

这表明 paste 已收到 > 作为参数，并试图打开该名称的文件.不存在这样的文件.因此消息.

This indicates that paste had received > as an argument and was trying to open a file by that name. No such file exists. Therefore the message.

作为 shell 命令行，可以使用该名称创建文件:

As the shell command line, one can create a file by that name:

touch '>'

如果存在这样的文件，当 subprocess 使用 shell=False 调用 paste 时，会使用该文件作为输入.

If such a file had existed, paste, when called by subprocess with shell=False, would have used that file for input.

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