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

my $le = 'lethal_results.txt';

open my $in, '<', $le or die "Cannot open $le:$!\n";

while (<$in>) {
    chomp;
    my $foo = (split)[4];
    print "$foo\n" if $foo >= 50;
}

close $in;

##</code><code>##

perl -lane 'print $F[4] if $F[4] >= 50' < lethal_results.txt