Windows文件重定向无法在python脚本中运行

Question

The following line of python code opens a new windows cmd prompt and executes the ipconfig command but fails to redirect the output to a file I give it.

os.system("start cmd /k ipconfig > {file_name}")

If I do the same command directly into a cmd prompt, it has no problem with the redirection. Any idea why this might fail?

Answer 1

If I type this command at a command prompt

start cmd /k ipconfig > {file_name}

it doesn't redirect the output from ipconfig . It opens a new console and in that console it runs ipconfig , sending output to the screen. start produces no output of its own, so the > redirects non-existent output from start to {filename} and creates a zero-byte output file.

To do the redirection using start you need to associate the > with ipconfig like this:

start cmd /k "ipconfig > {file_name}"

But if you're planning to invoke a shell from a Python program, it's usually not handy to open a console window and leave it there. If I type this simpler command at the command prompt

ipconfig > {file_name}

it works as you describe. Likewise,

os.system(r"ipconfig > C:\users\.blah.\{file_name}")

will work in Python, but you need to specify the path of the output file, because otherwise os.system() will probably try to send the file to a default location that you're not permitted to write to (because it is a subfolder of Program Files ). Use an r -string so that you don't have the hassle of doubling backslashes.

And consider using the subprocess module in preference to os.system .