String Methods

Updated Aug 24, 2023 ·

count

The count method lets you find how many times a character or set of characters appears in a string.

text = "Hello World"

puts text.count("l")        # Output: 3
puts text.count("w")        # Output: 0
puts text.count("lo")       # Output: 5
puts text.count("Wl")       # Output: 4

Notes:

• Searching for "l" counts only lowercase L
• "lo" counts all lowercase L's and O's combined, not sequences
• "Wl" counts uppercase W and lowercase L together

reverse

Calling reverse returns a new string where all characters appear in the opposite order, while the original string remains unchanged.

word = "Ruby"
value = "A1#b"

puts word.reverse
puts value.reverse

The output shows that reverse simply changes character order without altering character types or casing.

ybuR
b#1A

insert

The insert method adds characters into a string at a specific position without removing or replacing existing characters.

• Adds characters at a chosen index
• Works with one or multiple characters
• Can use positive or negative indexes

Examples:

1. Inserting at a specific index:

   text = "GorgeWashington"
   text.insert(5, "e ")
   puts text

   Output:

   George Washington

2. Inserting multiple characters:

   text = "RubyIsFun"
   text.insert(4, " Really ")
   puts text

   Output:

   Ruby Really IsFun

3. Using negative indexes:

   text = "George Washigto"
   text.insert(-1, "n")
   puts text

   Output:

   George Washington

delete

The delete method removes characters from a string. You can target one or more characters, and it will remove all occurrences.

For example, if you have "cottage cheese" and want to remove all lowercase "c":

text = "cottage cheese"
text.delete("c")

Output:

"ottage heese"

You can also remove multiple characters at once. For "c" and "e":

text = "cottage cheese"
text.delete("ce")
# => "ottag hs"

Output:

"ottag hs"

The order of characters in the argument does not matter. "ce" or "ec" gives the same result. This is like combining multiple delete calls into one.

upcase and downcase

The upcase and downcase methods return new strings with changed letter casing.

• upcase converts letters to uppercase
• downcase converts letters to lowercase
• Only affects alphabetic characters

Example:

place = "city square"

puts place.upcase
puts place.downcase

Output:

CITY SQUARE
city square

swapcase

The swapcase method flips the casing of each letter.

• Uppercase becomes lowercase
• Lowercase becomes uppercase
• Numbers and symbols stay the same

Example:

place = "City Square"

puts place.swapcase

Output:

cITY sQUARE

capitalize

The capitalize method changes only the first character to uppercase and makes the rest lowercase.

• Capitalizes the first letter
• Lowercases all remaining letters

Example:

name = "john doe"

puts name.capitalize

Output:

John doe

Note that case methods always return a new string and leave the original unchanged.

• Original string stays the same
• New string is created in memory
• Assignment is required to keep the result

Example:

label = "maiN Street"
puts label.upcase         # Output: MAIN STREET
puts label.downcase       # Output: main street
puts label.swapcase       # Output: MAIn sTREET
puts label.capitalize     # Output: Main street

# Variable is not changed
puts label                # Output: maiN Street

To keep the result, store it in a variable:

label = "main street"
upper_label = label.upcase
lower_label = label.downcase
swapped = label.swapcase
capitalized = label.capitalize

index and rindex

The index method helps find the position of a character or substring in a string. It returns the first match as an integer or nil if not found.

• Search is case sensitive
• Index always counts from the start of the string
• Multiple characters are matched in order

index vs. rindex:

• index searches left to right from the start or given position
• rindex searches from the end of the string backward
• Both return positions relative to the start of the string

Examples:

1. Using index:

   fact = "I am Very Handsome"
   puts fact.index("I")
   puts fact.index("E")
   puts fact.index("am")
   puts fact.index("Z")

   Output:

   0
   6
   2
   nil

2. Searching from a specific index:

   puts fact.index("E", 3)
   puts fact.index("e", 7)

   Output:

   6
   17

3. Using rindex to search from the end of the string backward:

   puts fact.rindex("E")     # last "E" from end
   puts fact.rindex("e")     # last "e" from end

   Output:

   17
   17
   

empty?

The empty? method checks whether a string has zero characters.

• Returns true for strings with no characters
• Returns false for strings with any content
• Treats spaces as characters

An empty string is still a valid string object, but it contains no characters. Any character, including spaces or symbols, means the string is not empty.

text1 = ""
text2 = "A"
text3 = " "

puts text1.empty?
puts text2.empty?
puts text3.empty?

Output:

true
false
false

This shows that only strings with no characters return true, reinforcing that empty? checks for content inside a string.

nil?

The nil? method checks whether an object is the nil object.

• Available on all Ruby objects
• Returns true only for nil
• Useful when object type is unknown

Most objects, including strings, numbers, and arrays, will always return false. Only the nil object itself returns true.

value1 = "Hello"
value2 = nil

puts value1.nil?
puts value2.nil?

Output:

false
true

chars and each_char

There are multiple ways to loop through each character in a string.

• split('') - Convert a string into an array of characters
• chars - Get an array of characters directly
• each_char - Iterate over characters without converting to an array

You can either convert a string to an array first or use each_char to loop directly.

Examples:

1. Using split and each:

   vehicle = "spaceship"
   characters = vehicle.split('')
   
   characters.each do |char|
     puts "#{char} is awesome"
   end

   Output:

   s is awesome
   p is awesome
   a is awesome
   c is awesome
   e is awesome
   s is awesome
   h is awesome
   i is awesome
   p is awesome

2. Using chars:

   vehicle = "spaceship"
   vehicle.chars.each do |char|
     puts "#{char} is awesome"
   end

   Output is the same as no. 1.

   s is awesome
   p is awesome
   a is awesome
   c is awesome
   e is awesome
   s is awesome
   h is awesome
   i is awesome
   p is awesome

3. Using each_char:

   vehicle = "spaceship"
   vehicle.each_char do |char|
     puts "#{char} is awesome"
   end

   Output is the same as no. 1.

   s is awesome
   p is awesome
   a is awesome
   c is awesome
   e is awesome
   s is awesome
   h is awesome
   i is awesome
   p is awesome

Bang Methods

Bang methods are special string methods that make permanent changes to a string.

• End with an exclamation mark (!)
• Modifies the original string
• Do not return a new string

Consider the example below:

word = "noodles"
word.capitalize

puts word

Output:

noodles

Now, adding the bang (!):

word = "noodles"
word.capitalize!

puts word

Output:

Noodles

Some common bang methods:

• upcase! converts all letters to uppercase
• downcase! converts all letters to lowercase
• reverse! reverses character order
• swapcase! swaps letter casing

Example:

word = "NoOdLeS"

word.upcase!
puts word

word.downcase!
puts word

word.reverse!
puts word

word.swapcase!
puts word

Output:

NOODLES
noodles
seldoon
SELDOON