How to Use File.write in Ruby: Simple Guide

In Ruby, use File.write(filename, content) to create or overwrite a file with the given content. This method writes the string directly to the file and returns the number of bytes written.

Syntax

The File.write method takes two main arguments: the filename as a string and the content you want to write to the file. It overwrites the file if it exists or creates a new one if it doesn't.

• filename: The name or path of the file to write to.
• content: The string data to write inside the file.

ruby

File.write("example.txt", "Hello, Ruby!")

Example

This example shows how to write a simple greeting message to a file named greeting.txt. After running, the file will contain the text "Hello, Ruby!".

ruby

filename = "greeting.txt"
content = "Hello, Ruby!"
bytes_written = File.write(filename, content)
puts "Wrote #{bytes_written} bytes to #{filename}."

Output

Wrote 12 bytes to greeting.txt.

Common Pitfalls

Common mistakes when using File.write include:

• Not having write permission for the file or directory, causing errors.
• Expecting File.write to append content instead of overwriting.
• Passing non-string content without converting it to a string first.

Always ensure you have permission and convert data to string if needed.

ruby

wrong_content = 12345
# This will NOT raise an error because File.write converts content to string internally
File.write("number.txt", wrong_content)

# Explicit conversion is also fine
File.write("number.txt", wrong_content.to_s)

Quick Reference

Method	Description
File.write(filename, content)	Writes content to filename, overwriting if exists.
File.write(filename, content, mode: "a")	Appends content to filename (using mode option).
File.write(filename, content.to_s)	Ensures content is string before writing.

Key Takeaways

Use File.write(filename, content) to quickly write or overwrite files in Ruby.

File.write returns the number of bytes written to the file.

Make sure content is a string or convert it before writing.

File.write overwrites existing files; use append mode if needed.

Check file permissions to avoid write errors.