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

#text file about 70MB
my $datasource ="C:\\somelargetextfile.txt";
my $i=1;
open DATASOURCE, "$datasource" or die "Can't open $datasource: $!";
foreach my $line (<DATASOURCE>){
           print "$i - $line";
           $i++;
           }
close (DATASOURCE);