<=>

Provides a case-sensitive comparison operator for pathnames.

Pathname.new('/usr') <=> Pathname.new('/usr/bin')
    #=> -1
Pathname.new('/usr/bin') <=> Pathname.new('/usr/bin')
    #=> 0
Pathname.new('/usr/bin') <=> Pathname.new('/USR/BIN')
    #=> 1

It will return -1, 0 or 1 depending on the value of the left argument relative to the right argument. Or it will return nil if the arguments are not comparable.