Sinatra is a great Ruby web micro-framework.
Its docs are good! Here’s my minimal getting started guide.
Put this in app.rb:
require 'sinatra'
get '/' do
'homepage'
end
Install the dependencies:
$ gem install --user-install sinatra rackup
Run the app:
$ ruby app.rb
[2024-12-29 23:54:24] INFO WEBrick 1.8.1
[2024-12-29 23:54:24] INFO ruby 3.2.3 (2024-01-18) [x86_64-linux-gnu]
== Sinatra (v4.1.1) has taken the stage on 4567 for development with backup from WEBrick
[2024-12-29 23:54:24] INFO WEBrick::HTTPServer#start: pid=4104 port=4567
And it’s running on http://localhost:4567/ ! I’d have thought 5678 would have worked better with the music theme ;)
If you do actually want to change the port, add the following line:
set :port, 8000
You’ll notice that if you edit the code, it isn’t applied to the currently running server.
The official docs at https://sinatrarb.com/faq.html#reloading
recommend using an out-of-process approach (a rerun executable),
but I’d prefer to be able to run the app without any prefix.
# I prefer:
$ ruby app.rb
# over:
$ rerun ruby app.rb
I like to use the in-process reloader which you can install like so:
$ gem install --user-install sinatra-contrib
Then you can enable live reloading like so:
require 'sinatra/reloader'
They say it’s deprecated but I hope they don’t take it away.
Other than requiring more typing, I found the rerun approach to be slower to reload.
You’ll probably want to template a response. You can do it inline:
get '/' do
template = "<%= 3 + 3 %>"
erb template
end
But you’ll probably want to move it to its own file views/index.erb:
# app.rb:
get '/' do
erb :index
end
# views/index.erb:
<%= 3 + 3 %>
To pass variables to the template, put them in a :locals hash:
get '/' do
message = 'hi'
erb :index, :locals => { message: }
end
# views/index.erb:
The message is <%= message %>
(this example is using the hash key-value punning syntax { message: })
Result:
$ curl localhost:8000
Message is: hi