sub prog_replace_string {
	my $replace_this = shift;
	my $with_this  = shift;
	my $string   = shift;

	my $length = length($string);
	my $target = length($replace_this);

	for(my $i=0; $i<$length - $target + 1; $i++) {
		if(substr($string,$i,$target) eq $replace_this) {
			$string = substr($string,0,$i) . $with_this . substr($string,$i+$target);
		}
	}
	return $string;
}