CODEWITHSUNDEEP
python
Jack
Jack

Reputation: 3

re.search() function in python not finding substring

The substring 'Failed to connect to host' is not being found in the 'text' variable. I am fairly new to python and I would appreciate any help. 

import subprocess
import re

host = 'XXXXXXX'
output = subprocess.Popen(['/usr/bin/ssh', '-q', host, 'ifconfig|', 'grep', 'Mask'], stdout=subprocess.PIPE)
text = output.communicate()[0].decode('utf-8')
pattern = 'Failed to connect to host'

if re.search(pattern, text, re.IGNORECASE):
    print('found')
else:
    print('not found')

The expected result should be "found" since the text str contains the pattern but for some reason, the result is "not found".

Actual Output:

Failed to connect to host XXXXXXX port 22: No route to host
not found

Upvotes: 0

Views: 104

Answers (1)

saintamh
saintamh

Reputation: 176

It's because the error message is printed to stderr, but you're only matching against the text printed on stdout. If you try print(repr(text)) you'll see it prints ''.

Try adding stderr=subprocess.STDOUT to your Popen call, like this:

output = subprocess.Popen([...], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
#                                                        ^-- this

What it does is it redirects stderr to stdout. See the docs here: https://docs.python.org/3.7/library/subprocess.html#subprocess.STDOUT

Upvotes: 1

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