# File lib/hiera/backend/eyaml/subcommands/decrypt.rb, line 37
          def self.validate options
            sources = [:eyaml, :password, :string, :file, :stdin].collect {|x| x if options[x]}.compact
            Trollop::die "You must specify a source" if sources.count.zero?
            Trollop::die "You can only specify one of (#{sources.join(', ')})" if sources.count > 1
            options[:source] = sources.first

            options[:input_data] = case options[:source]
            when :stdin
              STDIN.read
            when :string
              options[:string]
            when :file
              File.read options[:file]
            when :eyaml
              File.read options[:eyaml]
            end
            options
          end