Python子进程Grep [英] Python Subprocess Grep

问题描述

这是我的：

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

它什么也没有返回。
我不完全确定我做错了什么，所以有人可以解释。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，但由于帮助页面指出它是不安全的。我需要帮助来完成这项工作，以便我的脚本不是不安全的。

解决方案

我认为你遇到了两个问题：

1. 这个调用：
   
   pre $ subprocess.Popen（['grep'， ％s * .log％userid] ...
   

   $ c> shell = True ，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一的字符串一个参数，你把两个单独的参数压缩成一个单独的字符串（换句话说，grep解释为 foo12 * .log as 模式进行搜索，而不是模式+文件列表）。

   
   
   

   您可以通过以下方式解决此问题：

     p = subprocess.Popen（['grep'，userid，'* .log'] ...）
    第二个问题是，同样没有 shell = True ，<$ c $ 

c> execvp 不知道 *。log 和passe直接与grep配合使用，而不需要通过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：



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

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

Here's what I have:

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

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.

解决方案

I think you're running up against two problems:

1. This call:

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

   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).

   You can fix this by saying:

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

2. 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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