Comparison between the p, puts, and print Methods in Ruby

Greetings, friends! In Ruby, there are multiple ways to output information to the screen:

• Kernel#puts
• Kernel#p
• Kernel#print

Notice that each of these methods belong to the Kernel class.

The puts method

It's very common to use the puts method to output information to the screen or a console such as irb, the "interactive ruby" shell.

puts "Greetings, friends!"
# OUTPUT: Greetings, friends!

The puts method actually prints a newline character after each value passed into it.

puts "hello", "world"

=begin OUTPUT:
hello
world
=end

The puts method will print each value in an array onto a new line as well.

puts ["pizza", "donuts", "potato"]

=begin OUTPUT:
pizza
donuts
potato
=end

It is important to note that the puts method calls an object's to_s (to string) method internally. We can prove this by creating our own class with a to_s method.

class Cat
  attr_reader :name

  def initialize(name)
    @name = name
  end

  def to_s
    "Cat: #{name}"
  end
end

cat = Cat.new("Whiskers")
puts cat # Cat: Whiskers

Another interesting detail about the puts method is that it returns nil.

def debug(value)
  puts value
end

debugValue = debug("hi") # this line will print "hi" but debugValue will equal nil
puts debugValue == nil # true

The p method

Let's now look at the p method and call it on an array.

p ["pizza", "donuts", "potato"]
# OUTPUT: ["pizza", "donuts", "potato"]

As mentioned in the previous article, the p method helps us print arrays out on a single line because it calls an object's inspect method instead of its to_s method. We can prove this by creating our own class with an inspect method.

class Cat
  attr_reader :name

  def initialize(name)
    @name = name
  end

  def inspect
    "Cat: #{name}"
  end
end

cat = Cat.new("Whiskers")
p cat # Cat: Whiskers

Keep in mind that the p method will still print a newline character after each value:

p "pizza", "donuts", "potato"

=begin
"pizza"
"donuts"
"potato"
=end

Unlike the puts method, the p method will return the value of the object passed into it and will not return nil.

def debug(value)
  p value
end

debugValue = debug("hi") # this line will print "hi" and debugValue will equal "hi"
puts debugValue == "hi" # true

The print method

The print method is very similar to the puts method, but it does not print a newline character. It will internally call an object's to_s method and return nil.

class Cat
  attr_reader :name

  def initialize(name)
    @name = name
  end

  def to_s
    "Cat: #{name}"
  end
end

cat = Cat.new("Whiskers")
print cat # Cat: Whiskers

We can prove that the print method returns nil, similar to the puts method:

def debug(value)
  print value
end

debugValue = debug("hi") # this line will print "hi" and debugValue will equal "hi"
puts "\n" # add new line ourselves
puts debugValue == nil # true

Conclusion

To summarize the differences between each of the three methods discussed in this tutorial:

• The puts method calls an object's to_s method followed by a newline character. It will also return a value of nil.
• The p method calls an object's inspect method followed by a newline character. It will return the value of the object passed into it.
• The print method calls an object's to_s method but does not add a newline character. It will return a value of nil.

Resources

• Kernel#puts
• Kernel#p
• Kernel#print