使用 certutil 和 Python 下载文件

Question

I'm trying to download file by calling cmd command through Python. When I run this command in cmd:

certutil -urlcache -split -f https://www.contextures.com/SampleData.zip c:\temp\test.zip

The file downloads without any issues, but when I run that command through Python, the file is not being downloaded. I tried:

import subprocess
command = "certutil -urlcache -split -f https://www.contextures.com/SampleData.zip c:\temp\test.zip"

subprocess.Popen([command])
subprocess.call(command, shell=True)

also:

os.system(command)

Any ideas why this doesn't work? Any help would be greatly appreciated.

Thanks!

Answer 1

First: problem can makes \\t which has special meaning in Python (and other languages) and you should use "c:\\\\temp\\\\test.zip" or you would have to use prefix r to create raw string r"c:\\temp\\test.zip"

Second: when you don't use shell=True then you need list like

["certutil", "-urlcache", "-split", "-f", "https://www.contextures.com/SampleData.zip", "c:\\temp\\test.zip"]

Sometimes people simply use split(' ') to create it

"certutil -urlcache -split -f https://www.contextures.com/SampleData.zip c:\\temp\\test.zip".split(" ")

And then you can test both versions

cmd = "certutil -urlcache -split -f https://www.contextures.com/SampleData.zip c:\\temp\\test.zip"

Popen(cmd.split(' '))

Popen(cmd, shell=True)

---

EDIT:

If you will have more complex command - ie. with " " inside string - then you can use standard module shlex and command shlex.split(cmd) . To keep \\\\ in path you may need `posix=False

import shlex

cmd = "certutil -urlcache -split -f https://www.contextures.com/SampleData.zip c:\\temp\\test.zip"

Popen(shlex.split(cmd, posix=False))

---

For example this gives incorrect list with 4 elements

'--text "hello world" --other'.split(' ')

['--text', '"hello', 'world"', '--other']

but this gives correct list with 3 elements

shlex.split('--text "hello world" --other')

['--text', 'hello world', '--other']

Answer 2

Also, a raw string can be specified that will not interpret escape sequences such as \\t .

Python 3.8.4 (tags/v3.8.4:dfa645a, Jul 13 2020, 16:46:45) [MSC v.1924 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print("now\time")
now     ime
>>> print(r"now\time")
now\time
>>> print('now\time')
now     ime
>>> print(r'now\time')
now\time