使用Python如何从Shell输出中提取版本号？

Question

I am still learning...

Using python I want to extract the version number from a shell output to determine if an upgrade is required.

I was able to use subprocess.call with shell=true , however i read this is a security issue and would like some advise on a better method. I then hit an AttributeError as it seems StrictVersion doesn't see the output as a integer, I think?

Here is what I am doing currently.

import subprocess
from distutils.version import StrictVersion


def updateAnsible():
    print 'Checking Ansible version'
    version = subprocess.call("ansible --version | grep 'ansible [0-9].[0-9].[0-9]' | awk '{ print $2 }'", shell=True)

    print version
    if StrictVersion(version) < StrictVersion('2.7.0'):
        print "Need to upgrade"
    else:
        print "Do not need to upgrade"

if __name__ == '__main__':
    updateAnsible()

I Expect the output of StrictVersion(version) to be 1.2.3

but what i get is the below

Checking Ansible version
1.2.3
Traceback (most recent call last):
0
  File "test.py", line 32, in <module>
    updateAnsible()
  File "test.py", line 26, in updateAnsible
    if StrictVersion(version) < StrictVersion('2.6.0'):
  File "python2.7/distutils/version.py", line 140, in __cmp__
    compare = cmp(self.version, other.version)
AttributeError: StrictVersion instance has no attribute 'version'

Process finished with exit code 1

Answer 1

The immediate and narrow issue is that subprocess.call() returns exit status (which will be 0 if the grep didn't fail, or 1 if it did), not output. This can be worked around by using check_output() instead:

version = subprocess.check_output(
    "ansible --version | awk '/ansible [0-9].[0-9].[0-9]/ { print $2; exit }'", shell=True
).strip().decode('utf-8')

If you want to avoid shell=True (commendable, but not actually an immediate security issue in your current use case), that might look like:

import re

av = subprocess.check_output(['ansible', '--version'])
match = re.match('^ansible (\d+[.]\d+[.]\d+)$', av.split(b'\n')[0].decode('utf-8'))
if match is None:
  raise Exception("Unable to get version number from ansible")
version = match.group(1)