<p>For a file containing the given class, SomeCoolClass, what would be the proper or standard filename?</p>

<pre>
 1. somecoolclass.rb
 2. some_cool_class.rb
 3. some-cool-class.rb
 4. SomeCoolClass.rb
</pre>

<p>or some other variation?</p>

<p>I noticed in the Ruby stdlib, versions 1, 2 and 3 are used.</p>

With just
Ruby
(i.e. not Rails), naming is only a convention.  In
Rails
the
convention
of using underscores is necessary (almost).
I think convention #2
```
lowercase_and_underscore.rb
```
is more common and looks pretty good, though an article
Here
says
```
lowercasenounderscore.rb
```
is the Ruby convention.
Pick either
which ever convention is more common or which ever one you like more.  The most important thing is to
be consistent within a project
.