String.include? / start_with? / end_with?

# Checks whether the string contains the specified substring.
string.include?(search_string)

# Checks whether the string starts with the specified prefix.
string.start_with?(prefix)

# Checks whether the string ends with the specified suffix.
string.end_with?(suffix)

sentence = "Ruby is an object-oriented language."

# Check whether a substring exists.
puts sentence.include?("Ruby")       # true
puts sentence.include?("Python")     # false
puts sentence.include?("ruby")       # false (case-sensitive)

# Check the beginning of the string.
puts sentence.start_with?("Ruby")    # true
puts sentence.start_with?("Python")  # false

# Multiple candidates can be specified.
puts sentence.start_with?("Python", "Ruby", "Java")  # true

# Check the end of the string.
puts sentence.end_with?("language.")  # true
puts sentence.end_with?("language")   # false

# Useful for URL validation.
url = "https://example.com"
if url.start_with?("https://")
  puts "This is a secure URL."  # This line is printed.
else
  puts "Not HTTPS."
end

# Useful for checking file extensions.
filename = "image.png"
puts filename.end_with?(".png", ".jpg", ".gif")  # true

include? checks whether the string contains the specified substring. Comparison is case-sensitive, so if you want a case-insensitive search, convert the string to a consistent case with downcase before comparing.

start_with? and end_with? both accept multiple arguments and return true if any one of them matches. They are handy in practical situations such as checking URL schemes or file extensions.

To get the position (index) of a substring, use index / rindex.