How can I call ruby function basename in puppet

Inside templates you have access to a scope object. All of the functions that you can access in the puppet manifests can be accessed via that scope object, although not via the same name. Prepend "function_" to the beginning of the function name. For example, here I included one template inside another: <%= scope.function_template("template2.erb") %>

http://reductivelabs.com/trac/puppet/wiki/PuppetTemplating has great documentation about the scope object inside templates. For really deep information about template and functions you can look inside lib/puppet/parser/templatewrapper.rb and lib/puppet/parser/functions.rb.

Here's Puppet's support matrix for ruby versions:

http://docs.puppetlabs.com/guides/platforms.html#ruby-versions

(UPDATE after OP updated to show error messages)

Puppet has installed itself into your system Ruby library location under /usr/lib/ruby/1.8/site_ruby/, which the homebrew ruby will not look at.

The top line of /usr/bin/puppet is #!/usr/bin/env ruby which runs the first ruby in your $PATH. So you can either adjust your $PATH variable or change that line to specifically run the system ruby, a'la:

#!/usr/bin/ruby