python subprocess.check_output提供错误的输出

Question

I have problem execute this code here

subprocess.check_output(['ps -ef | grep ftp | wc -l'],env=environ,shell=True)

When I execute from terminal

ps -ef | grep ftp | wc -l

I get "1" as output which is fine.

Now, I execute same code from my python files as subprocess.check_output and it gives me 2. That is strange. Any Ideas why is it happening. Here is the complete code:

 def countFunction():
    environ = dict(os.environ)
    return subprocess.check_output(['ps -ef | grep ftp | wc -l'],env=environ,shell=True)

 count = countFunction()     
 print count

EDIT: Just to update , I do not have any ftp connections on.So command line is printing 1 on command which is fine. Thanks Arvind

Answer 1

The grep command will find itself:

$ ps -ef | grep ftp
wallyk  12546 12326  0 16:25 pts/3    00:00:00 grep ftp

If you don't want that, exclude the grep command:

$ ps -ef | grep ftp | grep -v ftp
$

It would be better to drop the -f switch to ps so that the command line arguments are not searched. That way, it won't find the grep ftp running:

$ ps -e | grep ftp | wc -l