If I understand correctly what you need then the most simple example would be this:
The controller:
class UploadController < ApplicationController
def new
end
def create
name = params[:upload][:file].original_filename
path = File.join("public", "images", "upload", name)
File.open(path, "wb") { |f| f.write(params[:upload][:file].read) }
flash[:notice] = "File uploaded"
redirect_to "/upload/new"
end
end
The view:
<% flash.each do |key, msg| %>
<%= content_tag :div, msg, :class => [key, " message"], :id => "notice_#{key}" %>
<% end %>
<% form_tag '/upload/create', { :multipart => true } do %>
<p>
<%= file_field_tag 'upload[file]' %>
</p>
<p>
<%= submit_tag "Upload" %>
</p>
<% end %>
This would let you upload any file without any checks or validations which in my opinion isn't that usefull.
If I would do it myself then I would use something like validatable gem or tableless gem just tableless is not supported anymore. These gems would allow you to validate what you're uploading to make it more sane.
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