1

I have a file which contains data like this:

$ yum -- to install package
admin1,group,n,0123456,/usr/bin 
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin
----->#i have to insert a new line here
$cat -- to read contents of a file
admin1,group,n,0123456,/usr/bin
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin

First, I have to find the the word $ yum in the file and insert a new line before starting of the next word starting with $.

Some help with my code would be appreciated.

 with open("test.txt", "a") as myfile:
      for row in myfile:
            if re.match(r'$yum,i): 
                myfile.append("user2,group,0123456,/usr/bin")
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7
  • Is the file the input and the file with a new line the output? Commented Sep 6, 2015 at 12:01
  • 1
    Have you tried anything yet? Post your code so that we can help you with any problems that you have. Commented Sep 6, 2015 at 12:03
  • 1
    you don't need a regex Commented Sep 6, 2015 at 12:09
  • no that is the complete file, i have to insert a new line at "---> " this indicates where new line has to be entered. Commented Sep 6, 2015 at 12:15
  • with open ("fileone","a") as file: Commented Sep 6, 2015 at 12:17

2 Answers 2

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1

Opening the file with a does not allow you to file_object.append(..., it means when you write to the file content will be added to the end of the file so myfile.append("user2,group,0123456,/usr/bin") is not remotely valid syntax.

You can use itertools.groupby to group by section where lines start with a $, then either add a line if the line starts with $ yum or just write the lines as is:

from itertools import groupby
from tempfile import NamedTemporaryFile
from shutil import move

with open("in.txt") as f, NamedTemporaryFile("w",dir=".",delete=False) as out:
    grps = groupby(f,key=lambda x: x.startswith("$"))
    for k, v in grps:
        if k:
            val = next(v)
            out.write(val)
            if val.startswith("$ yum"):
                out.writelines(next(grps,[[], [""]])[1])
                out.write("I am a new line\n")
        else:
            out.writelines(v)
move(out.name,"in.txt")

The move(out.name,"in.txt") will change the original file content so the output will be:

$ yum -- to install package
admin1,group,n,0123456,/usr/bin 
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin
I am a new line
$cat -- to read contents of a file
admin1,group,n,0123456,/usr/bin
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin

Os use an inner loop every time you find a line starting with $ yum and breaking and writing the new line in the inner loop whenever you find the next $:

from tempfile import NamedTemporaryFile
from shutil import move

with open("in.txt") as f, NamedTemporaryFile("w",dir=".", delete=False) as out:
    for line in f:
        if line.startswith("$ yum"):
            out.write(line)
            for _line in f:
                if _line.startswith("$"):
                    out.write("I am a new line\n")
                    out.write(_line)
                    break
                out.write(_line)
        else:
            out.write(line)

move(out.name,"in.txt")
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Comments

0

Using fileinput.input() you can easily and safely overwrite the input file without explicitly using a secondary file and then overwriting the original file:

import fileinput

extra_line = 'new line here...'
seen_yum = False
f = fileinput.input('test.txt', inplace=True)
for line in f:
    if line.startswith('$ yum'):
        seen_yum = True
    elif line.startswith('$') and seen_yum:
        print extra_line
    print line,
f.close()

For the input:

some other lines
of no interest to us
$ yum -- to install package
admin1,group,n,0123456,/usr/bin
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin
$cat -- to read contents of a file
admin1,group,n,0123456,/usr/bin
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin

the output would be:

some other lines
of no interest to us
$ yum -- to install package
admin1,group,n,0123456,/usr/bin 
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin
new line here...
$cat -- to read contents of a file
admin1,group,n,0123456,/usr/bin
user2,group,n,0123456,/usr/bin
group,n,0123456,/usr/bin

It's not clear from your question whether the extra line should be inserted before every subsequent line that starts with $ - as the code above does. If you only want one extra line inserted for every $ yum seen you can reset the seen_yum flag.

import fileinput

extra_line = 'new line here...'
seen_yum = False
f = fileinput.input('test.txt', inplace=True)
for line in f:
    if line.startswith('$ yum'):
        seen_yum = True
    elif line.startswith('$') and seen_yum:
        seen_yum = False
        print extra_line
    print line,
f.close()

So if the file contains multiple lines that start with $ yum, and there is a following line that begins with $, a new line will be inserted.

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6 Comments

@mkhawke if $yum is found , we have to insert one new line or couple of line depending upon the requirement given to us . those lines has to be low $yum but above the line $(some other command )...basically i have a file given to me with same as present in server with some diff. i have to add those lines which are not there in old files in specific order.
Other than inserting multiple lines (if I understand that requirement) which is a trivial adaption of this code, how does this answer not satisfy that requirement?
@mkhawke , are we modifying the file also with the prinit statement ,? will the file be appended at the desire place? with the above code?
@Alekh: have you tried running the code? Yes, the file will be modified by using a print statement, and the new lines inserted at the required position. fileinput.input() works by redirecting sys.stdout to the file, so a normal print statement will write the file.
@mkhwke the above code writes the new line above the $ yum but i want that to be written below. please help..
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