#!/usr/bin/perl 
use strict;
use warnings;

for (qw <"system" "system.bak">){
	die "error..."
		if -e $_;
}

open SYSTEM_, "< system";
open SYSTEM_BAK, "> system.bak";

select SYSTEM_BAK;
while (<SYSTEM_>){
	print ;	
}

close SYSTEM_;
close SYSTEM_BAK;

system ("find ~/ > system");
system ("diff system system.bak");