Rake任务在读取文件时出现未定义的方法错误

Question

I've got a rake task that changes the meta tags on certain pages.

desc 'changes the meta tags'
task mixup_meta_tags: :environment do 
  meta_tags = ['index','noindex','index,nofollow','nofollow,noindex']
  new_tag = meta_tags.sample(1)[0]
  #
  #iterate through html docs
  base = 'app/views/site'
  pages = ['home','about','products','pricing']
  pages.each do |page|
    filename = base + '/' + page + '.html.haml'
    text = File.read(filename)
    current_tag = Nokogiri::HTML(File.open(filename, "r")).xpath("//meta[@name='robots']").first["content"]
    File.open(filename, "w") { |file| file << text.gsub(current_tag,new_tag)}
  end   
end

I'm getting a cryptic error message:

undefined method `[]' for nil:NilClass

concerning this line:

current_tag = Nokogiri::HTML(File.open(filename,"r")).xpath("//meta[@name='robots']").first["content"]

This line is supposed to figure out what the current tags are so that they can be replaced (via the next line of code).

Any advice on what's out of place here?

Answer 1

It's saying that

File.open(filename,"r")).xpath("//meta[@name='robots']").first

is nil or essentially

File.open(filename,"r")).xpath("//meta[@name='robots']").empty?  # true