open (FILE, "<$footer") or die "Couldn't open file $footer: $!";

##</code><code>##

open (FILE, "<$footer") or die "Couldn't open file $footer: $!";

while (my $line = <FILE>) {
  $line =~ s/something/something_else/g;
  
  # print changed line
  print $line;

  # do some very complicated other stuff here
}
close FILE;