$ perl -Mstrict -Mwarnings -MData::Dumper -E '
open my $dataFH, q{<}, \ <<EOF or die $!;
john, 100
barry, 300
john, 200
mary, 150
barry, 200
EOF

my %names;
while ( <$dataFH> )
{
    chomp;
    my( $name, $value ) = split m{\s*,\s*};
    $names{ $name } += $value;
}

print Data::Dumper->Dumpxs( [ \ %names ], [ qw{ *names } ] );'
%names = (
           'john' => 300,
           'barry' => 500,
           'mary' => 150
         );
$