#! perl -slw
use strict;

my $bigstring;
do{ local $/; $bigstring = <> };
close ARGV; print length $bigstring;

open RAMFILE, '<', \$bigstring or die $!;

my( $p, $index ) = ( 0, chr(0) x ( 4 * 10e7 ) );
vec( $index, ++$p, 32 ) = tell( RAMFILE ) while <RAMFILE>;

## print the 500,000th line of the file

my $n = 500,000;
print substr( $bigstring, vec( $index, $n, 32 ), vec( $index, $n+1, 32 ) - vec( $index, $n, 32 ) );

<STDIN>; ## pause to check memory size

__END__
[16:02:50.49] C:\test>dir test.dat
 Volume in drive C is Local Disk
 Volume Serial Number is 8C78-4B42

 Directory of C:\test

15/09/2016  23:47     1,020,000,000 test.dat
               1 File(s)  1,020,000,000 bytes
               0 Dir(s)  379,695,529,984 bytes free

[16:02:54.35] C:\test>wc -l test.dat
10000000 test.dat

[16:03:00.02] C:\test>head test.dat
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
####################################################################################################
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((
))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
****************************************************************************************************

[16:03:03.22] C:\test>1171361 test.dat
1010000000
5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555

# 1,774MB

[16:03:22.93] C:\test>