if elsif else and end

Ruby offers the expected if and else expressions for branching logic, terminated by the end keyword:

# Simulate flipping a coin
result = [:heads, :tails].sample

if result == :heads
  puts 'The coin-toss came up "heads"'
else
  puts 'The coin-toss came up "tails"'
end

In Ruby, if statements are expressions that evaluate to a value, and the result can be assigned to a variable:

status = if age < 18
           :minor
         else
           :adult
         end

Ruby also offers C-style ternary operators (see here for details) that can be expressed as:

some_statement ? if_true : if_false

This means the above example using if-else can also be written as

status = age < 18 ? :minor : :adult

Additionally, Ruby offers the elsif keyword which accepts an expression to enables additional branching logic:

label = if shirt_size == :s
          'small'
        elsif shirt_size == :m
          'medium'
        elsif shirt_size == :l
          'large'
        else
          'unknown size'
        end

If none of the conditions in an if/elsif chain are true, and there is no else clause, then the expression evaluates to nil. This can be useful inside string interpolation, since nil.to_s is the empty string:

"user#{'s' if @users.size != 1}"