Question

I’m using Windows 7, and I’ve tried this under Python 2.6.6 and Python 3.2.

So I’m trying to call this command line from Python:

netstat -ano | find ":80"

under Windows cmd, this line works perfectly fine.

So,

• 1st attempt:

  output = subprocess.Popen(
             [r'netstat -ano | find ":80"'],
             stdout=subprocess.PIPE,
             shell=True
  ).communicate()
  

  An error is raised that ‘find’ actually didn’t receive correct parameter (e.g. ‘find “:80” \’):

  Access denied - \
  

• 2nd attempt:

  #calling netstat
  cmd_netstat = subprocess.Popen(
                  ['netstat','-ano'],
                  stdout = subprocess.PIPE
  )
  
  #pipelining netstat result into find
  cmd_find = subprocess.Popen(
               ['find','":80"'],
               stdin = cmd_netstat.stdout,
               stdout = subprocess.PIPE
  )
  

  Again, the same error is raised.

  Access denied - \
  

What did I do wrong? 🙁

EDIT:

• 3rd attempt (As @Pavel Repin suggested):

  cmd_netstat = subprocess.Popen(
                  ['cmd.exe', '-c', 'netstat -ano | find ":80"'],
                  stdout=subprocess.PIPE
  ).communicate()
  

  Unfortunately, subprocess with [‘cmd.exe’,’-c’] results in something resembling deadlock or a blank cmd window. I assume ‘-c’ is ignored by cmd, resulting in communicate() waiting indefinitely for cmd termination. Since this is Windows, my bet bet is cmd only accepts parameter starting with slash (/). So I substituted ‘-c’ with ‘/c’:

  cmd_netstat = subprocess.Popen(
                  ['cmd.exe', '/c', 'netstat -ano | find ":80"'],
                  stdout=subprocess.PIPE
  ).communicate()
  

  And…back to the same error:

  Access denied - \
  

EDIT:
I gave up, I’ll just process the string returned by ‘netstat -ano’ in Python. Might this be a bug?

Answer 1

So I revisited this question, and found two solutions (I switched to Python 2.7 sometime ago, so I’m not sure about Python 2.6, but it should be the same.):

1. Replace find with findstr, and remove doublequotes

   output = subprocess.Popen(['netstat','-ano','|','findstr',':80'],
                             stdout=subprocess.PIPE,
                             shell=True)
                      .communicate()
   

   But this doesn’t explain why “find” cannot be used, so:

2. Use string parameter instead of list

   output = subprocess.Popen('netstat -ano | find ":80"',
                             stdout=subprocess.PIPE,
                             shell=True)
                      .communicate()
   

   or

   pipeout = subprocess.Popen(['netstat', '-ano'], 
                              stdout = subprocess.PIPE)
   output = subprocess.Popen('find ":80"', 
                             stdin = pipeout.stdout, 
                             stdout = subprocess.PIPE)
                      .communicate()
   

The problem arise from the fact that: [‘find’,'”:80″‘] is actually translated into [‘find,’\”:80\”‘].
Thus the following command is executed in Windows command shell:

>find \":80\"
Access denied - \

Proof:

• Running:

  output = subprocess.Popen(['echo','find','":80"'],
                            stdout=subprocess.PIPE,
                            shell=True)
                     .communicate()
  print output[0]
  

  returns:

  find \":80\"
  

• Running:

  output = subprocess.Popen('echo find ":80"',
                            stdout=subprocess.PIPE,
                            shell=True)
                     .communicate()
  print output[0]
  

  returns:

  find ":80"