Add lines to text file after occurence of certain text

Question

I have a text file that I needs to manipulate. I want to add a line after occurence of word "exactarch". Means whenever "exactarch" occurs, I want to add text in the next line.

E.g. If this is the original file content,

[main]
cachedir=/var/cache/yum
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
distroverpkg=redhat-release
tolerant=1
exactarch=1
gpgcheck=1
plugins=1

I want to change it as below:

[main]
cachedir=/var/cache/yum
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
distroverpkg=redhat-release
tolerant=1
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1

This is what I tried to do:

with open('file1.txt') as f:
    for line in input_data:
        if line.strip() == 'exactarch':  
            f.write('obsoletes=1')

Obviously this is not working as I can't figure out how can I count and write to this line.

Read in the whole file as a list of lines, do your insertion in the list and then write out the whole list to a file — sshashank124, May 19 '15 at 07:51
Are you working on GNU/Linux or some system that has `sed` installed? — , May 19 '15 at 07:51

score 4 · Answer 1 · 2015-06-03T11:58:57.130

4

You ask for a Python solution. But tasks like this are made to be solved using simpler tools.

If you are using a system that has sed, you can do this in a simle one-liner:

$ sed '/exactarch/aobsoletes=1' < in.txt

What does this mean?

sed: the executable
/exactarch/: matches all lines that contain exactarch
a: after the current line, append a new line with the following text
obsoletes=1: the text to append in a new line

Output:

[main]
cachedir=/var/cache/yum
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
distroverpkg=redhat-release
tolerant=1
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1

Edit:

To modify the file in place, use the option -i and the file as an argument:

$ sed -i '/exactarch/aobsoletes=1' in.txt

edited Jun 03 '15 at 11:58

answered May 19 '15 at 07:56

This just prints output on console. How can I insert in actual file? – Abhishek dot py May 25 '15 at 11:10
To write the output to a *different* file, add `> out.txt` to the command line. To modify the file in place, use the option `-i`. – May 25 '15 at 11:47
Not working. I am using sed -i '/exactarch/aobsoletes=1' < in.txt. I need to modify the file in place. – Abhishek dot py Jun 03 '15 at 10:32

score 3 · Accepted Answer · answered May 19 '15 at 08:02

Simple - read all lines, find correct line and insert desired line after found. Dump result lines to file.

import os 
with open('lines.txt') as f:
    lines = f.readlines()

lines.insert(lines.index('exactarch=1\n') + 1, 'obsoletes=1\n')
with open('dst.txt', 'w') as f:
    for l in lines:
        f.write(l)

score 2 · Answer 3 · edited May 23 '17 at 12:30

2

The past says it's pretty simple - replacing words in files is not a new thing.

If you want to replace a word, you can use the solution implemented there. In your context:

import fileinput

for line in fileinput.input(fileToSearch, inplace=True):
    print(line.replace("exactarch", "exactarch\nobsoletes=1"), end='')

edited May 23 '17 at 12:30

Community

1
1

answered May 19 '15 at 07:57

A. Abramov

1,823
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Miles · Answer 4 · 2015-05-20T06:22:45.267

I am hesitant using fileinput, b/c if something goes wrong during the 'analysis' phase you are left with a file in whatever conditions it was left before the failure. I would read everything in, and then do full work on it. The code below ensures that:

Your inserted value contains a newline value '\n' if it's not going to be the last item.
Will not add duplicate inserted values by checking the one below it.
Iterates through all values incase multiple "exactarch=1"s were added since the snippet last ran.

Hope this helps, albeit not as stylish as a one/two liner.

with open('test.txt') as f:
    data = f.readlines()

insertValue = 'obsoletes=1'

for item in data:
    if item.rstrip() == 'exactarch=1': #find it if it's in the middle or the last line (ie. no '\n')
        point = data.index(item)

        if point+1 == len(data): #Will be inserted as new line since current exactarch=1 is in last position, so you don't want the '\n', right?
            data.insert(point+1, instertValue)
        else:
            if data[point + 1].rstrip() != insertValue: #make sure the value isn't already below exactarch=1
                data.insert(point+1, insertValue + '\n')
                print('insertValue added below "exactarch=1"')
            else:
                print('insertValue already exists below exactarch=1')

with open('test.txt','w') as f:
    f.writelines(data)

Add lines to text file after occurence of certain text

4 Answers4