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

use Tie::File;

my $obj = tie my @file, 'Tie::File', 'file.big' || die "Unable to tie 'file.big': $!";
my $big = 1024 * 1024;

for ( 0 .. $#file - 1 ) {
    my $beg = $obj->offset($_);
    my $end = $obj->offset($_ + 1);
    next if $end - $beg > $big;
    # process $file[$_];
}

# Handle last line as special case
my $beg = $obj->offset($#file);
my $end = -s 'file.big';
if ( $end - $beg <= $big ) {
    # process $file[-1];
}

#Cleanup
undef $obj;
untie @file;