In Ruby, how does puts _|_ work?

Question

I am confused with how puts _|_ works in Ruby. If you type in a variable and then call that statement

3
puts _|_

you get the name of the variable followed by nil

 3
 => nil

However, if you type it again, you get false

puts _|_
=> false

It doesn't seem like one of those Perl-like variables that begin with a dollar sign.

What in the world does this weird symbol mean and how does it work?

Answer 1

The underscore in a console (IRB or pry) stands for the result of the previous command. So

3
=> 3
puts _|_
3
=> nil

Here the above puts statement becomes equivalent to

puts 3 <bit-wise or> 3

which puts 3|3 equals puts 3.

Since puts returns nil, when you repeat the puts _|_ it becomes

puts nil|nil

... which is puts false.