Understanding The Differences Between Puts, Print & P

There are many ways to print something in Ruby.

Here are the most useful:

• puts
• print
• p

But how are these different?

And when should you use one or the other?

That’s what you’re going to learn in this article!

How to Print Without A Newline

When you want to print something on the screen for the user to see, you normally use puts.

Like this:

puts "Hello there!"

Puts automatically adds a new line at the end of your message every time you use it.

If you don’t want a newline, then use print.

Example:

print 123

The next time you print something it will be one the same line as your last message.

Example:

print 123
print 456
print 789

123456789

But if you use puts:

puts 123
puts 456
puts 789

123
456
789

Every message has its own line!

Puts also treats arrays in a different way.

Example:

puts [1,2]
1
2

print [1,2]
[1,2]

Here’s another difference:

Puts attempts to convert everything into a string (by calling to_s).

Why is that important?

Because if you’re trying to puts an array with nil values…

It’s going to show some blanks lines!

Example:

puts [1,nil,nil,2]
1


2

To summarize, puts & print:

• Convert things to strings, even if that means an empty string

Only puts:

• Adds a new line to the end of your messages
• Displays array elements one-per-line

Debug Output With P

What about puts vs p?

p is a method that shows a more “raw” version of an object.

For example:

> puts "Ruby Is Cool"
Ruby Is Cool

> p "Ruby Is Cool"
"Ruby Is Cool"

What is p useful for?

Debugging.

When you’re looking for things like (normally invisible) newline characters, or you want to make sure some value is correct, then you use p.

Another difference:

• puts always returns nil
• p returns the object you pass to it

This is a more technical difference…

But it can show up if you try to puts a variable as the last line of a method, and you’re using the return value of that method.

Example:

def numbers
  puts 123
end

numbers
# nil

In this example, the numbers method will display 123 on the screen, but its return value will be nil.

If you try:

result = numbers

Then result will be nil, instead of 123.

But if you use p then it will work.

Pretty Printing

Ruby has yet another printing method.

Called pp.

This is like p, but it prints big hashes & arrays in a nicer way.

Note that older version of Ruby (pre 2.4) need to do require 'pp' to get access to this method.

Video Tutorial

Summary

You’ve learned about the differences between puts, print & p in Ruby!

Now it’s practice time.

If you practice with something new immediately you’ll integrate this information into your knowledge base, if you don’t practice you’ll forget & you’ll not make progress.