What does !! mean in ruby?

? is used to represent single character string literals. Like ?a,?b but not ?ab.

To answer the comment of OP :

Yes, they are.

irb(main):001:0> ?x + 'y'
=> "xy"
irb(main):002:0> 'x' + 'y'
=> "xy"

$>  "/" == ?/ 
=> true

another version of string but shorter :) also true: %{/}

In Ruby 1.8.x series, it return ASCII value

alok@alok-desktop:~$ rvm use ruby-1.8.7-p370
Using /home/alok/.rvm/gems/ruby-1.8.7-p370
alok@alok-desktop:~$ irb
1.8.7-p370 :001 > ?F
 => 70

In Ruby 1.9+ it returns same character string

1.9.2-p320 :018 > ?A
 => "A"

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