String Methods

String methods are the built-in operations Ruby provides for transforming and inspecting text — changing case, trimming whitespace, splitting, searching, and replacing — and they make text wrangling one of Ruby's great pleasures.

Learn String Methods in our free Ruby course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick reference.

Part of the free Ruby course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

You'll use interpolation, upcase / strip / split / join , gsub , format , and the in-place bang methods like gsub! .

What You'll Learn in This Lesson

1️⃣ Interpolation, Case & Trimming

Inside double quotes, # { ... } drops any expression into a string. The case methods upcase , downcase , capitalize , and swapcase reshape letters, while strip removes surrounding whitespace and chomp removes a trailing newline.

2️⃣ Split, Join & Repeat

split turns a string into an array of pieces (on whitespace by default, or on any delimiter you give it), and join stitches an array back into a string. The * operator repeats a string — handy for separators and banners.

3️⃣ Search, Replace, Format & Bang Methods

Ask questions with include? , start_with? , and end_with? . Replace text with sub (first match) or gsub (all matches), build formatted output with format / % , and reach for a bang method like upcase! when you want to mutate the original string.

Your turn. Fill in each ___ blank with the right method, then run it.

Mini-Challenge: Initials & a Censor

Chain split , map , and join to build initials, then use gsub with string repetition to censor a word. Run with ruby strings.rb .

Common Errors (and the fix)

• ❌ 'Hi # { name } ' printing literally → ✅ interpolation needs double quotes.
• ❌ Expecting capitalize to title-case → ✅ it only uppercases the first letter; split + map for each word.
• ❌ sub when you meant all matches → ✅ use gsub for every occurrence.
• ❌ Chaining on a bang method that returned nil → ✅ use the non-bang version, or store first.
• ❌ "5" + 5 raising a TypeError → ✅ convert: "5" + 5.to_s or interpolate.

Pro Tips

• 💡 Slugify in one line: str.downcase.strip.gsub(/\s+/, "-") .
• 💡 tr for swaps: "hello".tr("el", "ip") swaps characters faster than gsub.
• 💡 Frozen by default soon: add # frozen_string_literal: true at the top to make literals immutable and faster.

📋 Quick Reference — String Methods

Concept

Ruby Syntax

Interpolate

"Hi # { name } "

Trim / newline

strip , chomp

Split / join

split(",") , join("-")

Replace all

gsub("a", "b")

Contains?

include?("x")

Format

format("%.2f", n)

Frequently Asked Questions

🎉 Lesson Complete!

• ✅ Interpolation with # { ... } in double quotes
• ✅ Case methods, plus strip and chomp
• ✅ split / join convert between strings and arrays
• ✅ gsub replaces all, sub replaces the first
• ✅ format / % for output; bang methods mutate in place
• ✅ Next lesson: Advanced Enumerable

Practice quiz

Continue this course

• Previous: case/when Conditionals
• Next: Advanced Enumerable