very easy, look

If in Debian-Based type:

apt-get install libsqlite3-dev

and so:

gem install sqlite3-ruby

you see this message:

Building native extensions. This could take a while...
Successfully installed sqlite3-ruby-1.2.4
1 gem installed
Installing ri documentation for sqlite3-ruby-1.2.4...
Installing RDoc documentation for sqlite3-ruby-1.2.4...
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