use File::Copy;
open(RFH, "<ReadFile.h") or die "Trying:$!";
open(WFH, ">WriteFile.h") or die "Trying:$!";
while(<RFH>) {
  s/search/replace/;
  print WFH;
}

close RFH;
close WFH;

move ("WriteFile.h", "ReadFile.h") or die "With a vengance:$!";

##</code><code>##

$^I = '.old';
@ARGV = ("header.h");
while (<>) {
   s/search/replace/;
   print;
}