Puppet custom facts check zabbix user

Facter.add(:zabbix_user) do
    confine :kernel => :linux
    setcode do
    %x{grep zabbix /etc/passwd |cut -f1 -d:}.chomp
    end
end

if $zabbix_user == "zabbix"

/usr/lib/ruby/site_ruby/1.8/facter/util/directory_loader.rb:75: command not found: /var/lib/puppet/facts.d/zabbix_user.rb

/var/lib/puppet/facts.d/zabbix_user.rb: line 1: syntax error near unexpected token `:zabbix_user'
/var/lib/puppet/facts.d/zabbix_user.rb: line 1: `Facter.add(:zabbix_user) do'
Fact file /var/lib/puppet/facts.d/zabbix_user.rb was parsed but returned an empty data set