From: "Bartosz Dziewoński" <matma.rex@...>
Date: 2013-05-29T07:48:31+09:00
Subject: Re: AAARRRRGH! s="#$" => SyntaxError: compile error

Ah, I've found it now: the hash is treated as beginning string interpolation, the $ as the beginning of a global variable name, the quote as the rest of variable name, and then you have no closing quote.

Compare this with:

irb(main):001:0> $a = 5
=> 5
irb(main):003:0> "#{$a}"
=> "5"
irb(main):002:0> "#$a"
=> "5"
irb(main):004:0> "#{$"}"
=> (lots of stuff)

("#$"" is valid, too, but doesn't work in IRB.)

Also see http://bugs.ruby-lang.org/issues/5156 , reporting this issue, closed as "Rejected".

-- 
Matma Rex