Find all lines that match regex pattern and grab part of string

Question

f = open("machinelist.txt", 'r')
lines = f.readlines()
for host in lines:
       hostnames = host.strip()
       print hostnames

Returns:

\\TESTHOSTDEV01
\\TESTHOSTDEVDB01
\\TESTHOSTDEVDBQA
\\TESTHOSTDEVQA02
\\BTLCMOODY01          MRA Server
\\BTLCSTG05            StG Server
\\BTLCWEB02
\\BTLCWSUS01           Test Update Server
\\HIMSAPP01
\\SLVAPP01
\\TORAAPP01
\\HNSVAPP01
\\TESAPP01

I am curious if there is a way to use re.findall() to grab all lines that begin with "\" however I just want to capture return the hostnames, not the "\ or the comments after the host such as "MRA Server" (example: BTLCMOODY01)

Ashwini Chaudhary · Accepted Answer · 2013-08-30 15:48:38Z

3

You can do something like this(no need of regex):

Use str.startswith to check if a line starts with '\\':

>>> strs = "\\BTLCMOODY01          MRA Server\n"
>>> strs.startswith('\\')
True

Then use a combination of str.split and str.lstrip to get the first word:

>>> strs.split(None, 1)
['\\BTLCMOODY01', 'MRA Server\n']  
#apply str.lstrip on the first item
>>> strs.split(None, 1)[0].lstrip('\\')
'BTLCMOODY01'

Code:

>>> with open('abc1') as f:
...     for line in f:
...         if line.startswith('\\'):     #check if the line startswith `\`
...             print line.split(None,1)[0].lstrip('\\') 
...             
TESTHOSTDEV01
TESTHOSTDEVDB01
TESTHOSTDEVDBQA
TESTHOSTDEVQA02
BTLCMOODY01
BTLCSTG05
BTLCWEB02
BTLCWSUS01
HIMSAPP01
SLVAPP01
TORAAPP01
HNSVAPP01
TESAPP01

edited Aug 30, 2013 at 15:48

answered Aug 30, 2013 at 15:43

Ashwini Chaudhary

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Comments

Birei · Accepted Answer · 2013-08-30 15:44:15Z

2

An approach using regular expression:

import re

f = open("machinelist.txt", 'r')
lines = f.readlines()
for host in lines:
    hostnames = host.strip()
    if hostnames.startswith('\\'):
        print(re.match(r'\\\\(\S+)',hostnames).group(1))

It yields:

TESTHOSTDEV01
TESTHOSTDEVDB01
TESTHOSTDEVDBQA
TESTHOSTDEVQA02
BTLCMOODY01
BTLCSTG05
BTLCWEB02
BTLCWSUS01
HIMSAPP01
SLVAPP01
TORAAPP01
HNSVAPP01
TESAPP01

answered Aug 30, 2013 at 15:44

Birei

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1 Comment

C Dubya Over a year ago

Ah Birei, I think get it now. group(1) would be any string of characters but that ofcourse would be the (\S+) after "\\\\"

Patt Mehta · Accepted Answer · 2013-08-30 16:55:33Z

0

import re

pattern = re.compile(r"\\([a-z]+)[\s]+",re.I) # single-slash, foll'd by word: \HOSTNAME  

fh = open("file.txt","r")

for x in fh:
    match = re.search(pattern,x)
    if(match): print(match.group(1))

edited Aug 30, 2013 at 16:55

answered Aug 30, 2013 at 15:45

Patt Mehta

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1 Comment

Ashwini Chaudhary Over a year ago

Don't use file.readlines(loads everything into memory), you can iterate over the file object itself.

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