Cryptic Ruby Global Variables and Their Meanings

For a longer list (though the explanations are briefer), see Zenspider's Ruby QuickRef[1]. It also includes a handy listing of predefined global constants[2] (and a lot more).[3]<p>[1]: <a href="http://zenspider.com/Languages/Ruby/QuickRef.html#pre-defined-variables" rel="nofollow">http://zenspider.com/Languages/Ruby/QuickRef.html#pre-define...</a><p>[2]: <a href="http://zenspider.com/Languages/Ruby/QuickRef.html#pre-defined-global-constants" rel="nofollow">http://zenspider.com/Languages/Ruby/QuickRef.html#pre-define...</a><p>[3]: <a href="http://zenspider.com/Languages/Ruby/QuickRef.html" rel="nofollow">http://zenspider.com/Languages/Ruby/QuickRef.html</a>

This is one area where Matz kept too much of Perl. Thankfully, it's rare to see Ruby programmers making heavy use of these.

When using the debugger you can sometimes end up in an exception handler that doesn't provide a way to get access to said exception. $! can be a life-saver to help figure out what's going on, eg.<p><pre><code> (rdb:1) list 11 do_something_stupid 12 rescue =&#62; 13 log("Something went wrong") 14 end (rdb:2) e $! #&#60;Errno::ENOENT: No such file or directory - /tmp/durr&#62;</code></pre>

I rarely see those used except when you look at codegolf contests. There you can find all of those variables put to good and creative use :)