#!/usr/bin/perl

use strict;
use warnings;

my $in_qfn  = '...';
my $out_qfn = '...';

open( my $in_fh, "<:raw", $in_qfn )
   or die( "Can't open `$in_qfn`: $!\n" );

open( my $out_fh, ">:raw", $out_qfn )
   or die( "Can't create`$out_qfn `: $!\n" );

my $int_size = 4; # length( pack( "L<", 0 ) );

local $/ = \( 8 * 1024 );

while ( my $in_buf = <$in_fh> ) {
   length( $in_buf ) % $int_size == 0
      or die( "Invalid input file `$in_qfn`\n" );

   my @ints = unpack( "L<*", $in_buf );

   # Something that modifies `@ints` here.

   print( $out_fh pack( "L<*", @ints ) )
      or die( "Error writing to `$out_qfn`: $!\n" );
}

close( $in_fh )
   or die( "Error reading from `$in_qfn`: $!\n" );

close( $out_fh )
   or die( "Error writing to `$out_qfn`: $!\n" );
[download]

Without readline (<>) and print:

#!/usr/bin/perl

use strict;
use warnings;

my $in_qfn  = '...';
my $out_qfn = '...';

open( my $in_fh, "<:raw", $in_qfn )
   or die( "Can't open `$in_qfn`: $!\n" );

open( my $out_fh, ">:raw", $out_qfn )
   or die( "Can't create`$out_qfn `: $!\n" );

my $blk_size = ( stat( $in_fh ) )[ 11 ] || 16384; 
my $int_size = 4; # length( pack( "L<", 0 ) );

$blk_size % $int_size == 0
   or die( "Invalid block size\n" );

my $in_buf = '';
while ( 1 ) {
   my $bytes_read = sysread( $in_fh, $in_buf, $blk_size, length( $in_b
+uf ) );
   defined( $bytes_read )
      or die( "Error reading from `$in_qfn`: $!\n" ) ;
   $bytes_read
      or last;

   my @ints = unpack( "L<*", $in_buf );
   substr( $in_buf, 0, @ints * $int_size, "" );

   # Something that modifies `@ints` here.

   {
      my $out_buf = pack( "L<*", @ints );
      my $total_to_write = length( $out_buf );
      my $total_written = 0;
      while ( $total_to_write ) {
         my $bytes_written = syswrite( $out_fh, $out_buf, $blk_size, $
+total_written );
         defined( $bytes_written )
            or die( "Error writing to `$out_qfn`: $!\n" );

         $total_written  += $bytes_written;
         $total_to_write -= $bytes_written;
      }
   }
}

length( $in_buf ) == 0
   or die( "Invalid input file `$in_qfn`\n" );

close( $in_fh )
   or die( "Error reading from `$in_qfn`: $!\n" );

close( $out_fh )
   or die( "Error writing to `$out_qfn`: $!\n" );
[download]