Programming Ruby 3.3

Handling Exceptions

Here’s some simple code that uses the open-uri library to download the contents of a web page and write it to a file, line by line:

tut_exceptions/fetch_web_page/fetch1.rb

require "open-uri"
URI.open("https://pragprog.com/news/index.html") do |web_page|
  output = File.open("index.html", "w")
  while (line = web_page.gets)
    output.puts line
  end
  output.close
end

What happens if we get a fatal error halfway through? We certainly don’t want to store an incomplete page to the output file.

Let’s add some exception-handling code and see how it helps. To start exception handling, we enclose the code that could raise an exception in a begin/end block and use one or more rescue clauses to tell Ruby ...