Remove indentation from all lines, based on the first one.

unindent.rb

class String
  def unindent
    _, spaces = *match(/^([\t ]+)/)
    spaces ? gsub(%r[^#{spaces}]ms, "") : self
  end
end

html = <<-CODE.unindent
            THIS IS JUST A TEST
              AND THIS A TEXT SNIPPET THAT SHOULD
              BE INDENTED ONLY TWO SPACES FROM LEFT.
CODE