String methods

Case and Whitespace

.upcase

Convert all characters to uppercase.

"hello".upcase 

→ "HELLO"

.downcase

Convert all characters to lowercase.

"HELLO".downcase 

→ "hello"

.strip

Remove leading and trailing whitespace.

"  hi  ".strip 

→ "hi"

.lstrip

Remove leading whitespace only.

.rstrip

Remove trailing whitespace only.

.chomp

Remove a trailing newline character. Useful after file_lines or user input.

.chop

Remove the last character unconditionally.

"hello!".chop 

→ "hello"

---

Inspection & testing

length

Number of characters.

"Frankie".length 

→ 7

.empty?

True if the string has zero characters.

"".empty? 

→ true

.nil?

Always false for a string; useful in nil-safe chains with &.

.include?(n)

True if n appears anywhere in the string.

"Frankie".include?("n")" 

→ true 

.start_with?(n)

True if the string begins with n.

"Frankie".start_with?("F") 
→ true 

.end_with?(s)

True if the string ends with s.

"Frankie".end_with?("e") 

→ true 

.count(sub)

Count non-overlapping occurrences of sub.

"hello".count("l") 

→ 2

---

Transformation

.reverse

Reverse the string character by character.

"Frankie".reverse 

→ "eiknarF"

.replace(old, new)

Replace the first occurrence of old with new. Alias for sub().

"Franpie".replace("p","k") 

→ "Frankie"

.delete(chars)

Remove all occurrences of any character in chars.

"hello".delete("l") 

→ "heo"

.squeeze

Collapse runs of consecutive identical characters.

"aaabbbccc".squeeze 

→ "abc"

.tr(from, to)

Translate characters — each character in from is replaced by the corresponding character in to.

"hello".tr("aeiou", "*") 

→ "h*ll*"

.center(width, pad)

Center in a field of width, padded with pad.

"hi".center(10, "-") 

→ "----hi----"

.ljust(width, pad)

Left-justify in a field of width.

"hi".ljust(10, "-") 

→ hi--------

.rjust(width, pad)

Right-justify in a field of width.

"hi".rjust(10, "-") 

→ --------hi

.encode

Convert string to a vector of byte values (UTF-8).

"hi".encode 

→ [104, 105]

---

Splitting & joining

.split(sep)

Split on a separator string, return a Vector.

"a,b,c".split(",") 

→ [a, b, c]

.join(sep)

Join a vector of strings with a separator. Called on a Vector but takes a string arg.

["a","b"].join("-") 

→ a-b

.lines

Split into a vector of lines, stripping newline characters

"a,b,c".lines 

→ [a,b,c]

.chars

Split into a vector of individual characters. Chains naturally into iterators.

puts "abc".chars 

→ [a b c]

.bytes

Return a vector of integer byte values.

puts "abc".bytes

→  [97, 98, 99]

.each_char do |c|

Iterate over each character with a block.

"Frankie".each_char do |c| 
  puts c 
end 

→ F
  r
  a
  n 
  k
  i
  e

.each_line do |l|

Iterate over each line with a block.

"Frankie is great!".each_line do |c| 
  c =  c.delete("i") 
  puts c 
end

→ Franke s great!

---

Slicing

[i]

Character at index i. Negative indices count from the end.

"hello"[-1] 

→ "o"

---

[a..b]

Inclusive slice from index a to b.

"hello"[1..3] 

→ "ell"

[a...b]

Exclusive slice — up to but not including b

"hello"[1...3] 

→ "el"

template(str, hash)

{{key}} placeholder replacement.

puts template("{{name}} is awesome!", {name: "Frankie"})

→ Frankie is awesome!

sprintf(fmt, args)

C-style formatting.

puts sprintf("%-10s %5d %8.2f", "Frankie", 1, 3.14444)

→ Frankie        1     3.14

.format(hash)

Named placeholder substitution. (introduced in v1.15)

Replaces {key} placeholders using values from the given hash. Raises a descriptive error if a key is missing.

puts "Hello, {name}! You have {count} messages.".format({name: "Alice", count: 5})
→ Hello, Alice! You have 5 messages.

puts "Order {id} placed by {user}".format({id: 42, user: "Bob"})
→ Order 42 placed by Bob

paste(a, b, sep)

Concatenate with separator.

puts paste("2026", "03", "14", sep: "/")

→ 2026/03/14

---

Pattern Extraction (introduced in v1.16)

.scan(pattern)

Find all non-overlapping matches of a regex pattern in the string. Returns a vector of matched strings (or capture groups if the pattern contains them).

# Extract all words
puts "hello world frankie".scan("[a-z]+")
# ["hello", "world", "frankie"]

# Extract email addresses
text = "Contact alice@example.com or bob@test.org for help."
emails = text.scan("[\\w.]+@[\\w.]+")
puts emails
# ["alice@example.com", "bob@test.org"]

# Extract dates
log = "Errors on 2026-01-15 and 2026-02-03."
dates = log.scan("\\d{4}-\\d{2}-\\d{2}")
puts dates
# ["2026-01-15", "2026-02-03"]

# Extract numbers
prices = "Items cost $12.50, $3.99, and $45.00."
amounts = prices.scan("\\d+\\.\\d{2}")
puts amounts
# ["12.50", "3.99", "45.00"]

scan is commonly combined with iterators:

html = "<a href='https://frankie.dev'>Frankie</a>"
urls = html.scan("href='([^']+)'")
urls.each do |url|
  puts "Found link: #{url}"
end