File Handling

What are you going to learn?

Understand how to create files with Ruby
Understand how to read files with Ruby
Be able to parse data from a file

Working with files with code is a very common pattern to deal with, on this lesson we will teach you how to create and manipulate them.

Creating a file

Ruby includes a File class to create, read and manipulate files.

A File is an abstraction of any file object accessible by the program and is closely associated with class IO.

This is how you would create a file with Ruby:

File.open("the_filename.txt", "w")
# This code creates a file named the_filename.txt, but can be whatever you want
# The second argument is the mode on which you wan to open a file, in this case write.

Here is a list of available modes for a file:

r - Read only. The file must exist.
w - Create an empty file for writing.
a - Append to a file.The file is created if it does not exist.
r+ - Open a file for update both reading and writing. The file must exist.
w+ - Create an empty file for both reading and writing.
a+ - Open a file for reading and appending. The file is created if it does not exist.

For more information about the open method, you can check out the official documentation

Reading a file

To easily read a file, you can just:

file = File.open("the_filename.txt", "r")
file.read # This reads the whole file and returns a string
file.rewind # Positions ios to the beginning of input, resetting lineno to zero. - https://ruby-doc.org/core-2.5.0/IO.html#method-i-rewind
file.readlines # Returns an array of each line of the file

In this case, the file must exist to be read.

You can also read each line of a file like this:

File.readlines("fruits.txt").each do |line|
  puts line.upcase 
end

Writing to a file

In order to write anything to a file you can do it like this:

file = File.open("the_filename.txt", "w")
file.write("Hello World!\n")
file.close

Exercises

Remember we have provided a repository with a bunch of exercises for you to complete. You can find it here