Step 3 – installing Ruby
Ruby is available in many different implementations and versions. Ruby 1.8.7 is still present on a lot of systems, but it's best avoided as it's incompatible with a lot of gems that you'll want to use.
Mac OS X comes with a preinstalled version of Ruby, but it is too old to be useful.
In such cases, you need to install a more recent version of Ruby.
At the time of writing, Ruby 1.9 is the recommended version. While Ruby 2.0 has just come out, it may cause some compatibility problems; so to start with, you should skip it.
Sinatra install 3
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