How to use Subprocess in Windows

Question

I am trying to save the result or function runcmd in the variable Result. Here is what I have tried: import subprocess

def runcmd(cmd):
  x = subprocess.Popen(cmd, stdout=subprocess.PIPE)
  Result = x.communicate(stdout)
  return Result
runcmd("dir")

When I run ths code, I get this result:

Traceback (most recent call last):
  File "C:\Python27\MyPython\MyCode.py", line 7, in <module>
    runcmd("dir")
  File "C:\Python27\MyPython\MyCode.py", line 4, in runcmd
    x = subprocess.Popen(cmd, stdout=subprocess.PIPE)
  File "C:\Python27\lib\subprocess.py", line 679, in __init__
errread, errwrite)
  File "C:\Python27\lib\subprocess.py", line 893, in _execute_child
    startupinfo)
WindowsError: [Error 2] The system cannot find the file specified

What could I do to fix this?

Chad Dienhart · Accepted Answer · 2013-11-06T18:34:36.923

16

I think what you are looking for is os.listdir()

check out the os module for more info

an example:

>>> import os
>>> l = os.listdir()
>>> print (l)
['DLLs', 'Doc', 'google-python-exercises', 'include', 'Lib', 'libs', 'LICENSE.txt', 'NEWS.txt', 'python.exe', 'pythonw.e
xe', 'README.txt', 'tcl', 'Tools', 'VS2010Cmd.lnk']
>>>

You could also read the output into a list:

result = []
process = subprocess.Popen('dir', 
    shell=True, 
    stdout=subprocess.PIPE, 
    stderr=subprocess.PIPE )
for line in process.stdout:
    result.append(line)
errcode = process.returncode
for line in result:
    print(line)

edited Nov 06 '13 at 18:34

answered Nov 06 '13 at 18:10

Chad Dienhart

5,024
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1

if both `stderr` and `stdout` are `PIPE` then you should consume them concurrently to avoid blocking the subprocess. It doesn't matter for `dir` (it is unlikely that it generates so much output on `stderr`) but it is a bad practice in general. You could use `result = subprocess.check_output("dir", shell=True).splitlines()` instead. – jfs Nov 06 '13 at 20:14

Erik Kaplun · Answer 2 · 2019-07-28T08:59:13.063

14

As far as I know, dir is a built in command of the shell in Windows and thus not a file available for execution as a program. Which is probably why subprocess.Popen cannot find it. But you can try adding shell=True to the Popen() construtor call like this:

def runcmd(cmd):
    x = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
    return x.communicate(stdout)

runcmd("dir")

If shell=True doesn't help, you're out of luck executing dir directly. But then you can make a .bat file and put a call to dir there instead, and then invoke that .bat file from Python instead.

btw also check out the PEP8!

P.S As Mark Ransom pointed out in a comment, you could just use ['cmd', '/c', 'dir'] as the value of cmd instead of the .bat hack if shell=True fails to fix the issue.

edited Jul 28 '19 at 08:59

answered Nov 06 '13 at 18:07

Erik Kaplun

37,128
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5

You could also use `["cmd", "/c", "dir"]` as the command if `shell=True` doesn't work. – Mark Ransom Nov 06 '13 at 18:31
@MarkRansom: probably a good idea—I'm not that familiar with Windows any more :) – Erik Kaplun Nov 06 '13 at 18:31
1

you could also use `subprocess.check_output` here – jfs Nov 06 '13 at 20:15
2

@MarkRansom It's better to use `%COMSPEC%` instead of hardcoding `cmd` :) – Piotr Dobrogost Nov 06 '13 at 21:06
How would `%COMSPEC%` be used? – Nov 07 '13 at 01:04
2

@user2961646: `cmd = os.environ.get('COMSPEC', 'cmd')`? – jfs Nov 08 '13 at 06:27

How to use Subprocess in Windows

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