LinuxQuestions.org - Python: find defined text string in a file, and replace the whole line

- Programming (https://www.linuxquestions.org/questions/programming-9/)

- - Python: find defined text string in a file, and replace the whole line (https://www.linuxquestions.org/questions/programming-9/python-find-defined-text-string-in-a-file-and-replace-the-whole-line-186924/)

Python: find defined text string in a file, and replace the whole line

Heya I really hope one or two python people are around. I've been looking around lately on the net for a solution to my problem. I want to mess with conf files on my system. Now they are meant to change values, therefore I can't exactly know what string I search for..

I've written something that finds and replaces a certain string in one file. All I found on the net was something that made a copy of the file and wrote the changes into the copy... So I made this, I couldn't get open("foo.txt", "r+w") to work for me :(

Code:

#! /usr/bin/python

# Preliminary code sample to start with..

import fileinput, string, sys

fileQuery = "usage.py"

sourceText = '''IPADDR[0]=""'''

replaceText = '''IPADDR[0]="192.168.1.102"'''

def replacemachine(fileName, sourceText, replaceText):

    ##################################################################

    file = open(fileName, "r") #Opens the file in read-mode

    text = file.read() #Reads the file and assigns the value to a variable

    file.close() #Closes the file (read session)

    file = open(fileName, "w") #Opens the file again, this time in write-mode

    file.write(text.replace(sourceText, replaceText)) #replaces all instances of our keyword

    # and writes the whole output when done, wiping over the old contents of the file

    file.close() #Closes the file (write session)

    print "All went well, the modifications are done"

    ##################################################################

replacemachine(fileQuery, sourceText, replaceText)

Now this would ONLY work if IPADDR[0] is = "" like what i search for... Is there a way to make a special sign that represents anything just like * does in bash ?
I know you can use variables inside a string like:
variableNeeded= cow
variable = "I love %s" % (variableNeeded)

Anyway I really hope to hear from anyone cause I am out of ideas (if the solution is followed up with a few links to places with lots of python info I wouldn't complain either :P )

Thanks in advance, and for your time!

Python has a regular expressions module. Check out python.org/doc for pretty much all the documentation you'll ever need.

Well, first of all, sed is probably a better tool for this, but ...

Code:

f = file(fileName)

newlines = []

for line in f:

    if 'IPADDR[0]' in line:

        # do the replacing here

    newlines.append(line)



outfile = file(outfileName, 'w')

outfile.writelines(newlines)

alternately, instead of using "if 'IPADDR[0]' in line" you could use a regexp on the line if you wanted.

Hello,

you may want to check out the scriptutil.py module.

It is providing functions for file searching and in-line string search/replace.

Code:

import fileinput

for line in fileinput.FileInput("file",inplace=1):

    if "IPADDR[0]" in line:

        line=line.replace(<old>,<new>)

        print line

to ghostdog74: thank you very much for pointing out the fileinput module!

Python indeed comes with the batteries included :)

The freplace() function (description here) should probably be refactored to make use of the fileinput module.

Quote:

Originally Posted by ghostdog74

Code:

import fileinput

for line in fileinput.FileInput("file",inplace=1):

    if "IPADDR[0]" in line:

        line=line.replace(<old>,<new>)

        print line

Here's another solution:

Code:

bbox33:trunk $ python

Python 2.4.4 (#1, May  9 2007, 11:05:23) 

[GCC 4.0.1 (Apple Computer, Inc. build 5367)] on darwin

Type "help", "copyright", "credits" or "license" for more information.

>>> import scriptutil as SU

>>> SU.freplace('.',

...            shellglobs=('file',), 

...            regexl=((r'IPADDR\[0\]', 'IPADDR[0]="192.168.1.102"', None),))

1

The freplace() function is described here.