def process_EnvArgumentNode(node)
      if node.single_quoted?
        debug_visit(node, 'single quoted argument, performing no expansion')
        node.lvalue
      else
        debug_visit(node, 'not singled quoted argument, performing variable expansion')
        variable_expand(node.lvalue)
      end
    end
def process_EnvArgumentNode(node)
      if node.single_quoted?
        debug_visit(node, 'single quoted argument, performing no expansion')
        node.lvalue
      else
        debug_visit(node, 'not singled quoted argument, performing variable expansion')
        variable_expand(node.lvalue)
      end
    end
process_EnvArgumentNode is separate from process_ArgumentNode since
 it doesn't allow full shell expansion. For example, the following
 will not be expanded to "FOO=a_1 a_2", it will be stored as provided:

   > FOO=a_{1,2}