Confused with Ruby's <=> operator

I am confused with Ruby开发者_如何学运维's <=> operator. How does it differ from == or ===? Any comprehensive examples/use case? Thanks.

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<=> is the combined comparison operator. it returns 0 if LHS equals RHS, 1 if LHS is greater than the RHS and -1 if LHS is less than RHs

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It's called the 'spaceship' operator. More info: What is the Ruby <=> (spaceship) operator? and http://en.wikipedia.org/wiki/Spaceship_operator

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== will NOT work in sort for example

[3,5,6,2,7].sort{|x,y| x <=>y }

== returns Boolean
<=> returns Fixnum (-1,0,1)