How to Write to a File in Ruby

The File class in Ruby has a write() method for writing to a file. The method returns the length written and ensures the file is automatically closed. It has the syntax below.

File.write('/your/file/path', 'Message content')

Let’s write a simple message to a file.

File.write('my-file.txt', 'A simlpe message.')

The above code helps us create a file called my-file.txt if it does not already exist and allows us to write A simple message. to the file. If the file already exists, the code overwrites the file and its content.

Instead of overwriting the file content, Ruby provides a way of appending to the content by specifying the mode option, and an example is shown below.

File.write('my-file.txt', " Another simple message\n", mode: 'a')

The \n in the example above is a new line character, and it means the following message we’ll be writing to this file should go to the following line. Let’s write another message to confirm this.

File.write('my-file.txt', 'This message should go on the next line', mode: 'a')

As a way of summarising the explanation above, let’s write a simple program that writes five lines of text to a file.

todos = [
  'wake up, shower, and leave for work',
  'Pick up John from school',
  'Meet with team to practice presentation',
  'Dinner with friends',
  'Relax and bedtime.'
]

todos.each_with_index do |todo, index|
  File.write('todo-list.txt', "#{index + 1}. #{todo}\n", mode: 'a')
end

Below is the todo-list.txt file content after running the program.

Output:

1. wake up, shower, and leave for work
2. Pick up John from school
3. Meet with team to practice presentation
4. Dinner with friends
5. Relax and bedtime.