Winn

For a project that I’m working on, I want to download a set of pictures from flickr once a day. In this way, my Rails app won’t need to access the flickr api – it can just grab the pics out of an images directory.

I figured that it would be an awfully easy task to download pictures from the internet using Ruby, and it is, but it was very difficult to find good examples. I googled for an hour or so, and kept coming up empty-handed. Finally, I checked in gmail where I keep mail from the Ruby Language mailing list. I found a relatively straightfoward way to do this.

Let’s say that you want to download a picture from flickr, and you know its URL. Here’s the ruby script to download the file:

require 'net/http'
Net::HTTP.start("static.flickr.com") { |http| 
   resp = http.get("/92/218926700_ecedc5fef7_o.jpg")
      open("fun.jpg", "wb") { |file|
         file.write(resp.body)
      }
}

The Net::HTTP class contains the magic needed to handle this operation. I don’t think this will work at all if you need to pull down a file from an FTP server. For now, we’re dealing with http urls. So, just strip off the “http://” portion of the url and everything after that up to the first / goes into the start method.

Now, we get the file. The rest of your image url after what you put in the start method goes into the get method. This grabs the file from flickr.

Now we’re going to copy the file down to where the script is running. First, let’s create the file we’re going to copy the picture into. Using the open method, the first parameter is the name of the file that you’re going to plop the picture into. We could have used “218926700_ecedc5fef7_o.jpg” or anything else here. The second parameter of the open method, “wb” indicates that we’re opening the file for (w)riting and we’re going to be writing (b)inary information. The “b” may not be necessary on non-Windows platforms.

Finally, we’re going to write into the new file, the contents or “body” of what we grabbed from flickr. So, this writes in the binary bits of the picture into fun.jpg. Remember that with the way that we created fun.jpg it’ll be in the same directory with our ruby script.

This same method will copy down .html files, .css files, .pdf’s and just about any other kind of file. In my next RubyNoob entry, I’ll write about how to combine this method with a flickr api call to grab an arbitrary number of recent photos from flickr. As usual, I’m still a noob, and there’s probably much better ways to do this. If you know a better way, please share in the comment section below.