Posted on Sep 9, 2019 • Edited on Oct 21, 2019

Ruby Puts vs Print vs P vs PP vs... Awesome?

When it's time to print something to the command line in Ruby, a developer has multiple options. While this can be useful, it can also be a bit confusing. Let's take a look at our options and see if we can clear up some of the confusion.

The five print methods in Ruby that we'll discuss are:

puts
print
p
pp
ap

For each of these methods, we'll go over how each prints to the command line and most importantly what they return. Knowing this is important, because not understand what a method returns can lead to a lot of bugs in your code, and ultimately, a lot of frustration.

Puts

Puts is the method that you'll find yourself using most often, so let's start there.

// ♥ irb 2.6.1 :001 > puts "Hello World!" Hello World! => nil

As we can see in Interactive Ruby Shell above, the puts method prints whatever you pass it to the command line followed by a newline character.

Puts will also print the individual elements of an array with the a newline character after each.

2.6.1 :001 > puts [1, 2, 3] 1 2 3 => nil

Puts also turns whatever you pass it into a string using the .to_s method. This causes any nil elements you may have in an array to be printed as an empty string.

2.6.1 :002 > puts [1, nil, nil, 4, 5] 1 4 5 => nil

We also see that puts returns nil. This is important because Ruby uses implicit returns so if you use a puts at the end of a method and you expect it to print the argument and return it, you'll be disappointed.

Let's take a look an example of this.

2.6.1 :002 > def test_of_puts (string) 2.6.1 :003?> puts string 2.6.1 :004?> end => :test_of_puts 2.6.1 :005 > return_value = test_of_puts ("Did I get returned?") Did I get returned? => nil 2.6.1 :006 > return_value => nil

Print

Next, let's take a look at print. Print is very similar to puts but there are a few differences. First of all, print also converts the argument you pass it into a string using .to_s and prints it to the command line. But it does not add a newline character.

2.6.1 :006 > def print_example 2.6.1 :007?> print 123 2.6.1 :008?> print 456 2.6.1 :009?> end => :print_example 2.6.1 :010 > print_example 123456 => nil

Another way that print differs from puts is that if you pass print an array, it will simply print out the array including the brackets.

2.6.1 :011 > print [1, 2, 3] [1, 2, 3] => nil

As we see in this example, print also returns nil. Sorry Gary Oldman.

Good call, Gary! Let's move on to the methods that don't return nil!

P

When we compare the p method to puts and print, we find some major differences. First of all, p prints the the raw object that you pass to it. This is because it uses .inspect to convert the object to a string rather than .to_s.

2.6.1 :001 > puts "Hello World!" Hello World! => nil 2.6.1 :002 > print "Hello World!" Hello World! => nil 2.6.1 :003 > p "Hello World!" "Hello World!" => "Hello World!" 2.6.1 :004 > p [1, 2, 3] [1, 2, 3] => [1, 2, 3] 2.6.1 :005 > p hash = {key1: "val1", key2: "val2", key3: "val3"} {:key1=>"val1", :key2=>"val2", :key3=>"val3"} => {:key1=>"val1", :key2=>"val2", :key3=>"val3"}

From this example, we can see that like puts, p adds a newline character to the end of the object that it prints. But p does not return nil. It returns that same object that was passed to it as an argument. This, combine the fact that p prints the raw object to the command line, makes p very useful when debugging.

PP

PrettyPrint, or pp, is a special version of p that is essential exactly the same except for the fact that it attempts to print large hashes and arrays to the command line in a more readable format.

2.6.1 :019 > pp ({ key1: 5, key2: { key21: 'val21', key22: 'val22', key23: 'val23' }, key3: { key31: 'val31', key32: 'val32', key33: 'val33' }, key4: [1, 2, 3, 4, 5] }) {:key1=>5, :key2=>{:key21=>"val21", :key22=>"val22", :key23=>"val23"}, :key3=>{:key31=>"val31", :key32=>"val32", :key33=>"val33"}, :key4=>[1, 2, 3, 4, 5]} => {:key1=>5, :key2=>{:key21=>"val21", :key22=>"val22", :key23=>"val23"}, :key3=>{:key31=>"val31", :key32=>"val32", :key33=>"val33"}, :key4=>[1, 2, 3, 4, 5]}

Well if you like pp, Gary, you're gonna love ap.

AP

Awesome_print, or ap, was created by Michael Dvorkin and though it is not included in the most recent version of Ruby, the gem can be install by entering the following into a terminal:

$ gem install awesome_print

Awesome_print one ups pp on a grand scale. Not only does it display nested hashes in a more readable format, but it also prints the index value next to each element of arrays.

2.6.1 :021 > ap ({ key1: 5, key2: { key21: 'val21', key22: 'val22', key23: 'val23' }, key3: { key31: 'val31', key32: 'val32', key33: 'val33' }, key4: [1, 2, 3, 4, 5] }) { :key1 => 5, :key2 => { :key21 => "val21", :key22 => "val22", :key23 => "val23" }, :key3 => { :key31 => "val31", :key32 => "val32", :key33 => "val33" }, :key4 => [ [0] 1, [1] 2, [2] 3, [3] 4, [4] 5 ] } => nil

I know, right?!?! Awesome_print brings me to tears too, Gary!

There's just one problem...ap returns nil.

I know Gary. I know. Life's like that sometimes. We don't always get everything we want. But now that we have a better understanding of how these five Ruby print methods work, we'll be better able to use the right tool for the right job.

References

DEV Community

Ruby Puts vs Print vs P vs PP vs... Awesome?

Puts

Print

P

PP

AP

References

Ruby Kernel verson: 2.6.1

Awesome_print

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