#!user/bin/perl -w

my $infile = '/home/me/Documents/Sample.txt';
my $outfile = '/home/me/Documents/Sample_Copy.txt';

open(IN, "< $infile") or die "Can't open $infile: $!";
binmode IN;

open(OUT, "> $outfile") or die "Can't open $outfile: $!";
binmode OUT;

my $blksize = (stat IN)[11] || 16384; 
print "\nBlock Size = $blksize\n";

my @bufAry = [];

while (my $len = sysread IN, my $buf, $blksize)
{ if (!defined $len)
  { next if $! =~ /^Interrupted/;
    die "System read error: $!\n";
  }

  @bufAry = unpack('I*', $buf);		# Disassemble buf into array.
	print "\nIn = " . scalar @bufAry;
  
  # Encryption subs here...
  
  undef($buf);				# Barrier to buf falling through.

	# Decryption subs here...
  
  $buf = pack('I*', @bufAry);		# Reassemble buf from array.
	print " Out = " . scalar @bufAry;
  
  $offset = 0;
  while ($len)
  { defined($written = syswrite OUT, $buf, $len, $offset)
    or die "System write error: $!\n";
		last if $written == 0;		# Avoid infinite loop.
    $len -= $written;
    $offset += $written;
  }
	print "\n";
}

close(IN);
close(OUT);