Hello, World

The smallest Ruby program, and the difference between puts, print and p.

Runs in Zerethon IDE · Ruby 4.0 Official Ruby documentation ↗

A Ruby file runs from top to bottom; there is no main to declare. #{...} inside double quotes inserts the value of any expression.

main.rb

puts "Hello, World!"
puts "Sum: #{2 + 3}"
print "a", "-", "b", "!\n"
p [1, "two", nil]

Output

Hello, World!
Sum: 5
a-b!
[1, "two", nil]

puts adds a newline after each argument; print adds nothing; p shows the value as Ruby code (strings in quotes, nil visible) — handy for debugging.
Single-quoted strings do not interpolate: '#{x}' prints the characters as written.
A line starting with # is a comment. Parentheses around method arguments are optional.

Official references