ok, here's a quick code for your reference. This is an implementation for :

Re^3: opening file for editing
by pvaldes (Scribe) on Oct 09, 2011 at 17:08 HKT

I guess that's the best option for you. So please re-read the logic from that post.

# code not tested!
my $srcFile = "/path/to/file.ext";

open F, "<", $srcFile; # this trip is READ
my @data = <F>;  # this can be danger if you have a big file
close F;

open F, ">", $srcFile; # this trip is WRITE
foreach my $line ( @data ) {
  $line =~ s/your_regex/expected_replacement/;
  print F $line;
}
close F;
[download]

HTH