String Methods

Strings come with dozens of built-in methods. These are the ones you'll reach for constantly.

Example

text = "  Hello, Ruby World  "

p text.strip
p text.strip.upcase
p text.strip.downcase
p "ruby".capitalize
p text.include?("Ruby")
p text.strip.start_with?("Hello")
p "a,b,c".split(",")
p "Ruby".reverse
p text.strip.sub("World", "Friends")
p "banana".gsub("a", "o")
p "banana".count("a")
p "Ruby"[0]
p "Ruby"[1..2]
p "".empty?

Expected output

"Hello, Ruby World"
"HELLO, RUBY WORLD"
"hello, ruby world"
"Ruby"
true
true
["a", "b", "c"]
"ybuR"
"Hello, Ruby Friends"
"bonono"
3
"R"
"ub"
true

Things to notice:

• Methods can be chained: text.strip.upcase strips first, then upper-cases the result.
• Methods ending in ? (include?, empty?) return true or false. That naming convention is used throughout Ruby.
• sub replaces the first match; gsub ("global substitute") replaces every match.
• Square brackets pick characters by position, starting from 0. "Ruby"[1..2] takes positions 1 through 2.

Bang methods

Most string methods return a new string and leave the original alone. Many have a "bang" version ending in ! that changes the original instead:

word = +"hello"
word.upcase
p word
word.upcase!
p word

"hello"
"HELLO"

The + before "hello" makes an explicitly mutable copy of the string. Plain string literals still work with bang methods in Ruby 3.4, but future versions plan to make literals frozen (unchangeable) by default, so the + keeps this example correct going forward. The Frozen Objects lesson in Level 2 explains why.

Common mistakes

• Calling name.upcase and expecting name itself to change. Either assign the result (name = name.upcase) or use upcase!.

Practice

Given email = " Ada@Example.COM ", print a cleaned-up version with no surrounding spaces, all in lowercase.

email = "  Ada@Example.COM "
puts email.strip.downcase

ada@example.com