title: Convert Ruby string to *nix filename-compatible string
body: <p>In Ruby I have an arbitrary string, and I'd like to convert it to something that is a valid Unix/Linux filename. It doesn't matter what it looks like in its final form, as long as it is visually recognizable as the string it started as. Some possible examples:</p>
  
  <pre><code>"Here's my string!" =&gt; "Heres_my_string"
  "* is an asterisk, you see" =&gt; "is_an_asterisk_you_see"
  </code></pre>
  
  <p>Is there anything built-in (maybe in the file libraries) that will accomplish this (or close to this)?</p>