Python 子进程 Grep [英] Python Subprocess Grep

问题描述

我正在尝试使用 subprocess 模块在 python 脚本中使用 grep 命令.

I am trying to use the grep command in a python script using the subprocess module.

这是我所拥有的:

userid = 'foo12'
p = subprocess.Popen(['grep', "%s *.log"%userid], stdout=subprocess.PIPE)

它什么都不返回.我不完全确定我做错了什么，所以有人可以解释一下.我正在使用的当前方法是通过添加 shell=true 使其输出正确的输出，但正如帮助页面指出的那样，它是不安全的.我需要帮助来完成这项工作，以免我的脚本不安全.

And it returns nothing. I am not entirely sure what I am doing wrong so can someone please explain. The current method that I am using that works is by adding the shell=true which makes it output the correct output but as the help pages have pointed out it is unsafe. I need help trying to make this work so that my script isn't unsafe.

推荐答案

我认为您遇到了两个问题:

I think you're running up against two problems:

1. 这个调用:

1. This call:

p = subprocess.Popen(['grep', "%s *.log"%userid]...

在没有 shell=True 的情况下不会按预期工作，因为参数列表直接传递给 os.execvp，这要求每个项目都是一个单独的字符串表示一个论点.您已将两个单独的参数压缩成一个字符串(换句话说，grep 将foo12 *.log"解释为模式搜索，而不是模式+文件列表).

will not work as expected without shell=True because the list of arguments are being passed directly to os.execvp, which requires each item to be a single string representing an argument. You've squished two separate arguments together into a single string (in other words, grep is interpreting "foo12 *.log" as the pattern to search, and not pattern+file list).

您可以通过以下方式解决此问题:

You can fix this by saying:

p = subprocess.Popen(['grep', userid, '*.log']...)

第二个问题是，同样没有 shell=True，execvp 不知道 *.log 是什么意思> 并将其直接传递给 grep，无需通过 shell 的通配符扩展机制.如果您不想使用 shell=True，您可以改为执行以下操作:

The second issue is that, again without shell=True, execvp doesn't know what you mean by *.log and passes it directly along to grep, without going through the shell's wildcard expansion mechanism. If you don't want to use shell=True, you can instead do something like:

import glob
args = ['grep', userid]
args.extend(glob.glob('*.log')
p = subprocess.Popen(args, ...)

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