unless can work in exactly the same way because unless is just the opposite of if:

age = 10
unless age >= 18
  puts "You're too young to use this system"
  puts "So we're going to exit your program now"
  exit
end

1.	Syntax of the full unless statement:
2.	unless statement simply operates in the logically reverse sense from the if statement
3.	To get the opposite effect of if you can use the word unless:

unless can work in exactly the same way because unless is just the opposite of if: : unless « Statement « Ruby