How can I comment multiple lines in Ruby?

Commenting multiple lines in Ruby isn’t quite the same as in languages like C or Java. While Ruby does support single-line comments (with #) and a form of multi-line commenting (=begin/=end), each approach has its own quirks. Below, you’ll learn how to comment out multiple lines effectively, along with best practices to keep your code clean and readable.

1. Multiple Single-Line Comments

The most common way to handle multi-line comments in Ruby is simply to place a # at the start of each line:

# This is line 1 of the comment
# This is line 2 of the comment
# This is line 3 of the comment

Pros and Cons

• Pros: Clear, unambiguous, and universally understood by Ruby developers.
• Cons: You need to prefix each line with a #, which can be time-consuming for very large blocks of text.

Many editors and IDEs have shortcuts to add (or remove) # from multiple selected lines, making this approach quite easy in practice.

2. =begin and =end for Block Comments

Ruby also allows block comments using =begin and =end. Everything between these keywords is treated as a comment:

=begin
This is a block comment in Ruby.
It can span multiple lines without using # on each line.
=end

puts "Hello, Ruby!"

Important Details

1. Must Start at the Beginning of the Line
   =begin and =end must appear at the start of a line (with no leading whitespace) for Ruby to recognize them correctly.

2. Commonly Used in Documentation
   This syntax is sometimes used in code documentation, but it’s far less common than single-line comments.

3. Can Be Confusing
   Some style guides discourage =begin/=end in favor of single-line comments for clarity and consistency.

3. When to Use Which Approach?

• Large Documentation Blocks: If you have extensive documentation (like method-level explanations or quick usage notes), =begin/=end can be handy—but be aware of style guide preferences.
• Small-to-Medium Comments: For most commenting needs, single-line # is simpler and more common.
• Editor Shortcuts: If your editor supports multi-line comment toggling, using multiple # lines is typically just as fast (and often more explicit).

Good Commenting Practices

1. Comment Why, Not What
   Explain the reasoning behind a particular approach rather than just restating what the code does.
2. Keep It Brief
   Over-commenting can clutter your code.
3. Stay Up-to-Date
   Outdated comments can mislead future maintainers. When you change the code, ensure your comments are still accurate.

Boost Your Ruby Skills

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• Grokking the Coding Interview: Patterns for Coding Questions
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Need hands-on guidance? DesignGurus.io also offers personalized Coding Mock Interviews and System Design Mock Interviews with ex-FAANG engineers to help you polish your skills and confidence.

Conclusion

You can comment multiple lines in Ruby using either multiple single-line comments (#) or a block comment with =begin and =end. While both are valid, single-line comments are most common and often preferable for clarity. Combine these techniques with good commenting practices to ensure your code is clear, maintainable, and easy to understand—no matter the size of your project.