So,I have to do a program which should do two things - extract a tar.gz file and add some lines of text
in some text files.The problem is adding the text.I should add a text in a file,but in a section which is determined so:
Section "Files"
...
here my lines of text
...
EndSection

Then another section in this file:
Section "Module"
...
Load "type1" //but must first determine if it is existing
Load "freetype" ////but must first determine if it is existing
...
EndSection

And also have to add lines here:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
*HERE I MUST ADD LINES*
</fontconfig>

So,can anybody tell me which functions should I use and then I will go to read docs.And maybe if
there are some techniques for these actions.

Thanks in advance