Introduction to the Command Line


Ruby is a programming language that can be used to perform tasks that would be difficult or cumbersome on the command line. To get started with Ruby, you need to install it. Usually, there is a program on your computer such as "Add/Remove Programs" or "Package Manager" which allows you to easily install Ruby. You can also go to, where you can find downloads for Ruby as well as more information on the language.

Just like the command line, you can either use Ruby by typing commands in individually, or you can create a script file. If you want to type commands in individually, install the "irb" program and use the irb command at the command line:

$ irb
> 10 + 10
=> 20
> exit

As you can see, you can use Ruby to do basic mathematics. An important note about Ruby is that instead of printing a value only when you use echo (which is puts in Ruby) , Ruby will print out the result of whatever command you enter -- this is what the "=>" means. When you enter the "10 + 10" command, the result is "20". Also, remember that you can use exit to get out of the irb program.

To write a multi-line script in Ruby, you create a file and save it with a ".rb" at the end. You can use any text editor to create this file -- Emacs, Vim, Gedit, or whatever your favorite is. A script could look like this:

a = 1 + 2
puts a

In this example, we create a variable, a, which stores the result of "1 + 2". It then uses the puts command to print out the result, which should be 3. If we save this file as ruby.rb, we can run it from the command line:

$ ruby ruby.rb

The Ruby program printed out "3", just like we expected. Of course, we can use Ruby to do more useful things. For example, we can look at all the files in a directory:

$ irb
> Dir.entries('my-directory')
=> ["ruby-script.rb", "other-script.rb", "document.odt", "photo.png"]

We used the Dir.entries method to look at the files in my-directory. You probably noticed that we pass parameters differently in Ruby. Instead of separating them with spaces, we surround them in parenthesis. We also need to enclose all words in quotes - not just ones that have special characters in them.

 Let's try doing something with these files -- here's a way to find all of the ".rb" files in a directory:

> files = Dir.entries('my-directory')
=> ["ruby-script.rb", "other-script.rb", "document.odt", "photo.png"]
> for file in files
> puts file if file.include?('.rb')
> end

First, we used the for command to loop through each of the files. We then get to work with each file. The next line says that we want to print out the file if it includes the text ".rb". Finally, we end the for loop.

We can also use command line code in Ruby by enclosing it in backticks. For example, if we wanted to delete all of the ".rb" files, we could use:

> files = Dir.entries('my-directory')
=> ["ruby-script.rb", "other-script.rb", "document.odt", "photo.png"]
> for file in files
> `rm #{file}` if file.include?('.rb')
> end

Notice how we enclosed the rm command in backticks. We also used #{} to enclose the Ruby variable, so it is put in to the command properly instead of the literal string "file".

Learning More About Ruby

If you want to learn more about Ruby, is the homepage for Ruby, and  is a great place to find tutorials and documentation.