How to use subprocess.Popen with built-in command on Windows

Question

In my old python script, I use the following code to show the result for Windows cmd command:

print(os.popen("dir c:\\").read())

As the python 2.7 document said os.popen is obsolete and subprocess is recommended. I follow the documentation as:

result = subprocess.Popen("dir c:\\").stdout

And I got error message:

WindowsError: [Error 2] The system cannot find the file specified

Can you tell me the correct way to use the subprocess module?

Solution

You should use call subprocess.Popen with shell=True as below:

import subprocess

result = subprocess.Popen("dir c:", shell=True,
                          stdout=subprocess.PIPE, stderr=subprocess.PIPE)

output,error = result.communicate()

print (output)

More info on subprocess module.

Comments

[Eryk Sun]

Using shell=True for internal shell commands such as set and dir is generally a bad idea. The output uses a lossy ANSI encoding. Windows environment variables and filesystem names are UTF-16, so generally internal shell commands should be run with the /u /c option to make cmd output UTF-16. The output then has to be decoded as 'utf-16le'. It can't be done with shell=True because /c /u is in the wrong order.