while(<DATA>){
  ...
  my $line = $_;
  ...
}

##</code><code>##

while(my $line = <DATA>){
  ...
}

##</code><code>##

use warnings;
use strict;

use Data::Dumper;
use List::Util qw(sum);

my %seen;

while (<DATA>) {
    chomp;
    $seen{$_}++;
}

print Dumper \%seen;
my $total = 0;

$total += $_ for values %seen;
print $total;

print sum( values %seen ); # sum from List::Util
__DATA__
james
dave
mike
ken
jon
jon
ken
jon
mike
james
dave
mike
ken
jon
jon