#!/usr/bin/perl -w
use strict;
my %hash = ( foo => '123' , bar => '234',
             batz => '345', bongo => '100' );

#send reference to hash, and list of keys to sum
print sum_hash( \%hash, 'foo', 'bar', 'batz' ) . "\n";

#send reference to hash, will sum all numeric values
print sum_hash( \%hash ) . "\n";

sub sum_hash {
    my $t_hash = shift;
    my $total;
    if (@_) {
        for (@_) {$total += $t_hash->{$_}; }
    }
    else {
        for ( keys %$hashref ) { $total += $t_hash->{$_}; };
    }
    return $total;
}