Interpolation and Formatting
Build strings with values.
Interpolation and Formatting is a free Ruby Academy lesson on CoddyKit. This is lesson 2 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, and your progress syncs across the web and the CoddyKit app. The Ruby Academy course includes 4 lessons in total.
String Interpolation
Interpolation lets you embed Ruby expressions inside a double-quoted string using #{ }. The expression is evaluated and inserted as text.
name = "Ada"
puts "Hello, #{name}!"Single vs Double Quotes
Interpolation only works in double-quoted strings. Single quotes treat #{ } as literal text.
x = 5
puts "value is #{x}"
puts 'value is #{x}'Expressions Inside Interpolation
You can put any Ruby expression in #{ }, including math and method calls.
a = 4
b = 6
puts "Sum is #{a + b}"
puts "Upper: #{"ruby".upcase}"Multiple Values
Combine several values into one readable sentence.
item = "book"
price = 12
puts "The #{item} costs #{price} dollars."Concatenation vs Interpolation
Interpolation is usually cleaner than + because Ruby auto-converts values to strings. With + you must call to_s yourself.
age = 30
puts "Age: " + age.to_s
puts "Age: #{age}"The format Method
format (alias sprintf) builds strings from a template. Use %s for strings and %d for integers.
result = format("%s scored %d", "Ada", 95)
puts resultFormatting Floats
Use %f for floats. Add a precision like %.2f to show two decimal places.
pi = 3.14159
puts format("Pi is %.2f", pi)
puts format("Pi is %.4f", pi)Padding Numbers
Width specifiers align output. %5d right-aligns in 5 spaces; %-5d left-aligns; %05d pads with zeros.
puts format("[%5d]", 42)
puts format("[%-5d]", 42)
puts format("[%05d]", 42)String % Operator
The % operator on a string is a shortcut for format. Pass a single value or an array of values.
puts "Hello, %s" % "World"
puts "%s is %d" % ["x", 10]Alignment with ljust and rjust
ljust and rjust pad a string to a given width. center centers it. Great for tables.
puts "abc".ljust(8, ".")
puts "abc".rjust(8, ".")
puts "abc".center(9, "-")Heredocs for Long Text
A heredoc writes multi-line text. The squiggly form <<~ strips leading indentation. Interpolation still works.
name = "Ada"
text = <<~MSG
Dear #{name},
Welcome aboard!
MSG
puts textQuick Check
Check your formatting knowledge.
Recap
You now build strings cleanly:
#{ }interpolation in double quotesformat/%with%s,%d,%.2fljust,rjust,centerfor alignment- heredocs for long multi-line text
Next: searching and replacing inside strings.
user = "Ada"
puts format("User %s ready", user)
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Frequently Asked Questions
Is the “Interpolation and Formatting” lesson free?
Yes — any 3 lessons of the Ruby Academy learning path, including “Interpolation and Formatting”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Ruby Academy course includes 4 lessons in total.
What will I learn in “Interpolation and Formatting”?
Build strings with values. You practise Ruby Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Ruby Academy?
No prior experience is required. Ruby Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 4.
How long does the “Interpolation and Formatting” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Ruby Academy lesson?
Yes. Every Ruby Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- String Basics and Methods
- Interpolation and Formatting
- Searching and Replacing
- Splitting and Joining