gistfile1.rb

string = "this is a string"

string.split("is")    #=> ["th", " ", " a string"]
string.split("is a")  #=> ["this ", " string"]

first, last = string.split("is a")

puts first  #=> "this "
puts last   #=> " string"

first, last = string.split("a string")
#=> ["this is "]

puts first  #=> "this is "
puts last   #=> nil

first, last = string.split("this is")
#=> ["", " a string"]

puts first  #=> ""
puts last   #=> " a string"