String slicing and indexing in Ruby

Introduction

String slicing and indexing let you pick out parts or single characters from a string, like cutting a piece from a loaf of bread.

You want to get the first letter of a name to make initials.

You need to extract a word from a sentence.

You want to check or change a specific character in a password.

You want to get a substring from a longer text for display.

Syntax

Ruby

string[index]
string[start, length]
string[range]

Indexing starts at 0 for the first character.

Negative indexes count from the end (-1 is last character).

Examples

Get single characters by index. 0 is first, -1 is last.

Ruby

name = "Ruby"
puts name[0]       # R
puts name[-1]      # y

Get a slice starting at index 0 with length 5.

Ruby

text = "Hello World"
puts text[0, 5]    # Hello

Get a slice using a range from index 5 to 11.

Ruby

phrase = "Good morning"
puts phrase[5..11]  # morning

Sample Program

This program shows how to get the first and last characters and a slice of the first word from a sentence.

Ruby

sentence = "Programming is fun"
first_char = sentence[0]
last_char = sentence[-1]
word = sentence[0, 11]
puts "First character: #{first_char}"
puts "Last character: #{last_char}"
puts "First word: #{word}"

Important Notes

If you use an index outside the string length, Ruby returns nil.

Ranges include both start and end indexes.

You can use negative indexes to count from the string's end.

Summary

String indexing starts at 0 and can be negative to count from the end.

Use [index] for single characters, [start, length] or [range] for slices.

Slicing helps extract parts of strings easily.