An Introduction to Ruby String Methods

Ruby String Methods

Ruby has many built-in methods to work with strings. Strings in Ruby by default are mutable and can be changed in place or a new string can be returned from a method.

Length:

  • The .length method returns the number of characters in a string including white-space.
"Hello".length #=> 5
"Hello World!".length #=> 12

Empty:

  • The .empty? method returns true if a string has a length of zero.
"Hello".empty? #=> false
"!".empty?     #=> false
" ".empty?     #=> false
"".empty?      #=> true

Count:

  • The .count method counts how many times a specific character(s) is found in a string.
  • This method is case-sensitive.
"HELLO".count('L') #=> 2
"HELLO WORLD!".count('LO') #=> 1

Insert:

  • The .insert method inserts a string into another string before a given index.
"Hello".insert(3, "hi5") #=> Helhi5lo # "hi5" is inserted into the string right before the second 'l' which is at index 3

Upcase:

  • The .upcase method transforms all letters in a string to uppercase.
"Hello".upcase #=> HELLO

Downcase:

  • The .downcase method transforms all letters in a string to lowercase.
"Hello".downcase #=> hello

Swapcase

  • The .swapcase method transforms the uppercase latters in a string to lowercase and the lowercase letters to uppercase.
"hELLO wORLD".swapcase #=> Hello World

Capitalize:

  • The .capitalize method make the first letter in a string uppercase and the rest of the string lowercase.
"HELLO".capitalize #=> Hello
"HELLO, HOW ARE YOU?".capitalize #=> Hello, how are you?

Note that the first letter is only capitalized if it is at the beginning of the string. ruby "-HELLO".capitalize #=> -hello "1HELLO".capitalize #=> 1hello

Reverse:

  • The .reverse method reverses the order of the characters in a string.
"Hello World!".reverse #=> "!dlroW olleH"

Split:

  • The .split takes a strings and splits it into an array, then returns the array.
"Hello, how are you?".split #=> ["Hello,", "how", "are", "you?"]
  • The default method splits the string based on whitespace, unless a different separator is provided (see second example).
"H-e-l-l-o".split('-') #=> ["H", "e", "l", "l", "o"]
  • To split a word in to individual letters :
"hello".split("") #=> ["h", "e", "l", "l", "o"]

Chop:

  • The .chop method removes the last character of the string.
  • A new string is returned, unless you use the .chop! method which mutates the original string.
"Name".chop #=> Nam
name = "Batman"
name.chop
name == "Batma" #=> false
name = "Batman"
name.chop!
name == "Batma" #=> true

Strip:

  • The .strip method removes the leading and trailing whitespace on strings, including tabs, newlines, and carriage returns ( \t , \n , \r ).
"  Hello  ".strip #=> Hello

Chomp:

  • The .chomp method removes the last character in a string, only if it’s a carriage return or newline ( \r , \n ).
  • This method is commonly used with the gets command to remove returns from user input.
"hello\r".chomp #=> hello
"hello\t".chomp #=> hello\t # because tabs and other whitespace remain intact when using `chomp`

To Integer:

  • The .to_i method converts a string to an integer.
"15".to_i #=> 15 # integer

Gsub:

  • gsub replaces every reference of the first parameter for the second parameter on a string.
"ruby is cool".gsub("cool", "very cool") #=> "ruby is very cool"
  • gsub also accepts patterns (like regexp ) as first parameter, allowing things like:
"ruby is cool".gsub(/[aeiou]/, "*") #=> "r*by *s c**l"

Concatenation:

  • Ruby implements some methods to concatenate two strings together:
  • The + method:
"15" + "15" #=> "1515" # string
  • The << method:
"15" << "15" #=> "1515" # string
  • The concat method:
"15".concat "15" #=> "1515" # string

Index:

  • The index method returns the index position of the first occurrance of the substring or regular expression pattern match in a string.
  • If there is no match found, nil is returned.
  • A second optional parameter indicates which index position in the string to begin searching for a match.
"information".index('o') #=> 3
"information".index('mat') #=> 5
"information".index(/[abc]/) #=> 6
"information".index('o', 5) #=> 9
"information".index('z') #=> nil

Clear:

  • Removes string content.
a = "abcde"
a.clear    #=> ""

Include?:

  • Returns true if the string contains the given string or character as an argument.
"abcde".include?("bc")  #=> true
"abcde".include?("pqr") #=> false