#!/usr/bin/perl -w
use strict;
my %hash;
my $val = "foo bar";
build_hash(\%hash,$val);

sub build_hash {
    my ($hash_ref, $val) = @_;
    my @vals = split /\s+/ , $val;
    foreach (@vals) {
        $hash_ref->{$_} = 1;
    }
}