I want to download a file on the Internet using Ruby and save it locally (with caution)


What if I want to use Ruby to download a file on the Internet and save it locally?


First is an example of a text file. If you want to download Wikipedia --HyperText Markup Language as an HTML file, write as follows.

require 'open-uri'

uri_str = 'https://ja.wikipedia.org/wiki/HyperText_Markup_Language'
URI.open(uri_str) do |res|
  IO.copy_stream(res, 'HyperText_Markup_Language.html')

The same is true for binaries like images. Download the image given as an example PNG file in Wikipedia --Portable Network Graphics.

require 'open-uri'

uri_str = 'https://upload.wikimedia.org/wikipedia/commons/4/47/PNG_transparency_demonstration_1.png'
URI.open(uri_str) do |res|
  IO.copy_stream(res, 'PNG_transparency_demonstration_1.png')


The ʻopen-uri library is a wrapper such as Net :: HTTP Net :: HTTPS Net :: FTPthat allows you to treat http and https URLs like regular files. This library redefinesKernel # open`, so you can also write:

require 'open-uri'

uri_str = 'https://upload.wikimedia.org/wikipedia/commons/4/47/PNG_transparency_demonstration_1.png'
open(uri_str) do |res|
  IO.copy_stream(res, 'PNG_transparency_demonstration_1.png')

However, starting with Ruby 2.7, opening URIs using Kernel # open, which is extended by ʻopen-uri`, has been deprecated. When I run the above code on Ruby 2.7, I get the following warning:

warning: calling URI.open via Kernel#open is deprecated, call URI.open directly or use URI#open

It doesn't mean that it doesn't stop just because of the warning, but it is recommended to use ʻURI # open or ʻOpenURI # open_uri.

Environmental information

$ ruby -v
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-darwin18

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