#!/usr/bin/perl
while ( defined ( $_ = <> ) ) {
  print;
  if ( /^line before your replacement/ ) {
    <>;
    print "LocalCompilerPresent=0\n";
  }
}
[download]

while (<>) {
  print;
  if  (m/TheLineBefore/){
    # read the line to be replaced
    my $line = <>;
    # do something with it
    $line =~ s/1/0/;
    # print the new version
    print $line;
 }
}
__DATA__
test data
more
TheLineBefore
LocalCompilerPresent=1
more stuff
[download]

Won't solve the problem.

• the OP asked to replace the instance(s) of LocalCompilerPresent=1 after the first one.
  Your script will only work if the wanted line is in the line immediately following the searched one. If there is a blank line in between, it will fail.
• Your script will print both the original and replaced lines.

I replace the line following the searched line. blank or not. Thats what I understand from the question.
And the script does NOT print both lines. Read the source again.
UPDATE: For some reason I answered to the wrong Node! Please Ignore. Sorry to the anon monk.
Boris

Your script will only work if the wanted line is in the line immediately following the searched one.

True. But I understood him as wanting to replace the immediately following line.

Your script will print both the original and replaced lines.

Really? What does it output for you? For me, it says

test data
more
TheLineBefore
LocalCompilerPresent=0
more stuff
[download]

which I take to be correct. No?

So it has to search for a line, replace 0 in the following line with a 1 and save that in the file.

You replace one line in a file by rewriting the whole file( at least that is the easiest way). So you can use one of the two snippets above (I believe both work, but there seems to be dissent, so check first) to read your .ini file and write the results to a new file. Check if it is good and then copy it over the original .ini file.

If you feel confident in the script you can also automatically have Perl overwrite the input file with the -i switch.

perl -i rep.pl config.ini
[download]

I'm having some trouble getting it to work.
Will you look at my code and see what could be wrong?



$cs="d:\\Perl\\Compiler_Setup.ini";

open cs or die "Cannot open $cs for read :$!";

while (<cs>) {
  if  (m/"Gimpel PC-Lint for H8]"/){
    # read the line to be replaced
    my $line = <cs>;
    # do something with it
    $line =~ s/1/0/;
    # print the new version
    print $line;
 }
}
[download]


Right now it just doesn't do anything.
in a command prompt I write
perl "replace test.pl"
and then it just goes back to d:\perl> as if it ran the program, and then just goes back to where I was before. It says:

D:\Perl>perl "replace test.pl"

D:\Perl>