[Ruby] string.split / array.join

str = "follow the yellow brick road"

print str.split("y") => ["follow the ", "ellow brick road"] 

print str.split("") => ["follow", "the", "yellow", "brick", "road"] #스페이스기준으로 쪼개기함

words = str.split("")
puts words[2] => yellow
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arr = ["hello", "world", "how", "are", "you"]
puts arr.join("") => hello world how are you
puts arr.join(_) => hello_world_how_are_you
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str = "follow the yellow brick road"
print str.split("o").join("x") => fxllxw the yellxw brick rxad