#!/usr/bin/perl -w 

$| = 1;

$in_file = 'very_large_text_file'; 
$out_file = 'parsed_text_file';

open(IN, "<$in_file");
open(OUT, ">$out_file");

while(<IN>){
  ($email, $other) = split(/\s+/,$_); 
  print OUT "$email\n";
}

close(OUT);
close(IN);