gistfile1.txt

[krzysztof@development tmp]$ cat test.erb 
<%= a[0] %>
[krzysztof@development tmp]$ cat test.pp 
class test {
  $a = ['a', 'b']

  file { "/tmp/test":
    content => template("/tmp/test.erb"),
    ensure  => present,
  }
}

include test
[krzysztof@development tmp]$ puppet test.pp 
notice: //test/File[/tmp/test]/ensure: created
[krzysztof@development tmp]$ cat test
a
[krzysztof@development tmp]$