When is the do keyword required in Ruby?

Question

For example, does the presence or absence of do in the following code affect the behavior of the program at all?

while true do
    puts "Hi"
    break
end

while true
    puts "Hi"
    break
end

Answer 1

According to The Ruby Programming Language book Section 5.2.1:

The do keyword in a while or until loop is like the then keyword in an if statement: it may be omitted altogether as long as a newline (or semicolon) appears between the loop condition and the loop body.

So, no, it won't change the behavior, it's just optional syntax.