Input and Output

All applications are fundamentally based on input and output.

Introduction

To create programs that are user friendly and interactive, you'll need to know how to output data to a screen and how to get input from a user. In this lesson, we'll cover the most common ways to achieve these tasks in Ruby. As with other lessons, and this one in particular, following along in irb or a REPL will be helpful.

Learning outcomes

By the end of this lesson, you should be able to do the following:

  • Differentiate between the print and puts commands.

  • Describe the method used to get input from the user.

Output commands

To output information, such as into your irb or REPL environment or into the command line, we can use the print command. To better show the differences between what Ruby is printing to the terminal and returning, the examples in this lesson use the full irb syntax, which is exactly what you'd see if you typed these commands into your own terminal irb session.

irb(main):001:0> print "Learning to code is FUN!"
Learning to code is FUN!=> nil

irb(main):002:0> print "1234"
1234=> nil

We can also use the puts command:

irb(main):001:0> puts "Learning to code is cool!!"
Learning to code is cool!!
=> nil

irb(main):002:0> puts "Hey, I want 2 key lime pies."
Hey, I want 2 key lime pies.
=> nil

irb(main):003:0> x = "My name is ALEX! :)"
=> "My name is ALEX! :)"

irb(main):004:0> puts x
My name is ALEX! :)
=> nil

As you can see, the puts and print commands are quite similar, but you should have already noticed the small difference between the two: puts appends a new line to the argument passed in, whereas print keeps things all on one line. A very important thing to notice for both commands is that after printing whatever argument they are passed, puts and print both return nil.

To highlight the difference between puts and print, we're going to pull out a piece of rarely used Ruby syntax: the semicolon. In short, semicolons are never required in Ruby, but they allow you to run multiple Ruby commands all on one line. This type of code golf is not generally recommended, but it's helpful for this example. In a REPL, such as repl.it, the two statements can be written on separate lines without the semicolon and still produce the desired output. However, irb can read only one statement at a time, making the semicolons necessary for this code to work as intended.

irb(main):001:0> print "Hello World"; print "I love drinking coffee"
Hello WorldI love drinking coffee=> nil

irb(main):002:0> puts "Hello World"; puts "I love drinking coffee"
Hello World
I love drinking coffee
=> nil

Input commands

To accept input from a user, we can use the gets command. When we use gets, program execution will stop and wait for user input. After the user presses Enter, the program will continue its execution.

Let's give this a go. Open irb, type gets, and then type Satoshi Nakamoto. You should see something like the following:

irb(main):001:0> gets
Satoshi Nakamoto
=> "Satoshi Nakamoto\n"

How about that? Let's break this process down a bit.

You'll notice that, unlike puts and print, gets actually returns the user input instead of returning nil. This means that the input can be assigned to a variable for you to then use and manipulate and twist and turn and spit back out.

As you might also remember from the String section of the Basic Data Types lesson, "\n" is an escape character that represents a new line. The gets command always returns a new line at the end of the input. This command often makes use of a "separator" to read streams and multi-line files, but that's beyond the scope of this beginner lesson. For now, it's helpful to know that #chomp is a method commonly used to trim separators.

irb(main):001:0> new_string = gets.chomp
This is a sentence.
=> "This is a sentence."

irb(main):002:0> puts new_string
This is a sentence.
=> nil

Assignment

  1. Read through the simple Hello, World lesson and exercise from www.learnrubyonline.org.

  2. Read the first four sections of the Ruby - File I/0 from TutorialsPoint on puts, gets, putc, and print.

  3. Read this article from Ruby Guides which describes the differences between puts, print and p.

Knowledge check

This section contains questions for you to check your understanding of this lesson. If you're having trouble answering the questions below on your own, review the material above to find the answer.

  • What are the two methods we can use to output data to the user's screen?

  • What is similar between these two output methods?

  • What is different between these two output methods?

  • What is the method you can use to get input from the user?

  • What is at least one difference between the output and input methods?

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