errors messages doesn't work in HTML ruby code - ruby-on-rails-4

Question

I am using rails 4.1.6 I looked at the active record validations site and follow their direction, but nothing is displayed in the HTML even if there is an error.
However, when I do it in rails console it works.
post = Post.new #create an empty post to test
post.valid? #false
post.errors.messages #this is successfully generate the error message array
However, it doesn't display any error messages in HTML. In fact "#post.errors" doesn't even run
-Ruby code in html
<%= form_for #post, :method => :post do |f| %>
<%= f.label :title %>
<%= f.text_field :title %>
<%= f.label :url %>
<%= f.text_field :url %>
<%= f.submit "Submit" %>
<% if #errors.any? %>
<ul>
<% #errors.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
<% end %>
<% end %>
-My PostsController
def create
# post = Post.new(title: params[:post][:title], url: params[:post][:url])
post = Post.new(post_params)
if post.save
redirect_to posts_path
else
#errors = post.errors.messages
redirect_to paths_path
end
end
private
def post_params
params.require(:post).permit(:title, :url)
end
-My post model
class Post < ActiveRecord::Base
validates :title, :length => {maximum: 140, minimum:1}, :presence => true
validates :title, :length => {maximum: 2083, minimum:1}, :allow_blank => true
end

Answer 1

When it comes to errors I do like to have a partial so I can keep my errors the same in the whole app like so:
app/views/shared/_errors.html.erb:
<% if object.errors.any? %>
<h5>The <%= t("activerecord.models.#{object.class.to_s.downcase}") %> could not be saved due to the following errors:</h5>
<ul>
<% object.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
<% end %>
And then for the views you want the errors to be displayed, just call:
<%= render 'shared/errors', object: #your_object %>
Hope this helps!

Answer 2

thanks for your help. Got some tip from my teacher it work. Simply use flash[:message] and it worked. Sorry for the trouble everyone
-My controller code
def create
post = Post.new(post_params)
if post.save
redirect_to :back
else
flash[:message] = post.errors.messages
redirect_to :back
end
end
-My HTML code
<%= simple_form_for #post, :method => :post do |f| %>
<%= f.label :title %>
<%= f.text_field :title %>
<%= f.label :url %>
<%= f.text_field :url %>
<%= f.submit "Submit" %>
<%= flash[:message] %>
<% end %>