#!/usr/bin/perl
$file = "new.txt";
open (IN,$file) || die "could not open  ".Sfile." for read";
@lines=<IN>;
close IN;
open (OUT,">", $file) || die "can not open file ".$file." for write";
foreach $line (@lines)
{
	$line =~ s/Hello/goodby/ig;
	print OUT $line;
}

close OUT;