Dec 9, 2014

Spider a Website with Wget – 20 Practical Examples

How do I download an entire website for offline viewing? How do I save all the MP3s from a website to a folder on my computer? How do I download files that are behind a login page? How do I build a mini-version of Google?


Wget is a free command line program – available for Mac, Windows and Linux (included) – that can help you accomplish all this and more. What makes it different from most download managers is that wget can follow the HTML links on a web page and recursively download the files. It is the same tool that a US soldier had used to download tons of secret documents from the army’s Intranet that were later published on the Wikileaks website.


You mirror an entire website with wget

You mirror an entire website with wget



How to Use Wget – Practical Examples


Wget is extremely powerful, but like with most other command line programs, the plethora of options it supports can be intimidating to new users. Thus what we have here are a collection of wget commands that you can use to accomplish common tasks from downloading single files to mirroring entire websites. It will help if you can read through the wget manual but for the busy souls, these commands are ready to execute.


1. Download a single file from the Internet

wget http://ift.tt/1vIGg56


2. Download a file but save it locally under a different name

wget ‐‐output-document=filename.html example.com


3. Download a file and save it in a specific folder

wget ‐‐directory-prefix=folder/subfolder example.com


4. Resume an interrupted download previously started by wget itself

wget ‐‐continue http://ift.tt/1vIGedo


5. Download a file but only if the version on server is newer than your local copy

wget ‐‐continue ‐‐timestamping http://ift.tt/QKGvIe


6. Download multiple URLs with wget. Put the list of URLs in another text file on separate lines and pass it to wget.

wget ‐‐input list-of-file-urls.txt


7. Download a list of sequentially numbered files from a server

wget http://ift.tt/1vIGedu


8. Download a web page with all assets – like stylesheets and inline images – that are required to properly display the web page offline.

wget ‐‐page-requisites ‐‐span-hosts ‐‐convert-links ‐‐adjust-extension http://ift.tt/1G9pBL0


Mirror websites with Wget


9. Download an entire website including all the linked pages and files

wget ‐‐execute robots=off ‐‐recursive ‐‐no-parent ‐‐continue ‐‐no-clobber http://example.com/


10. Download all the MP3 files from a sub directory

wget ‐‐level=1 ‐‐recursive ‐‐no-parent ‐‐accept mp3,MP3 http://example.com/mp3/


11. Download all images from a website in a common folder

wget ‐‐directory-prefix=files/pictures ‐‐no-directories ‐‐recursive ‐‐no-clobber ‐‐accept jpg,gif,png,jpeg http://ift.tt/1k1ZSxg


12. Download the PDF documents from a website through recursion but stay within specific domains.

wget ‐‐mirror ‐‐domains=abc.com,files.abc.com,docs.abc.com ‐‐accept=pdf http://abc.com/


13. Download all files from a website but exclude a few directories.

wget ‐‐recursive ‐‐no-clobber ‐‐no-parent ‐‐exclude-directories /forums,/support http://example.com


Wget for Downloading Restricted Content


Wget can be used for downloading content from sites that are behind a login screen or ones that check for the HTTP referer and the User Agent strings of the bot to prevent screen scraping.


14. Download files from websites that check the User Agent and the HTTP Referer

wget ‐‐refer=http://google.com ‐‐user-agent=”Mozilla/5.0 Firefox/4.0.1″ http://nytimes.com


15. Download files from a password protected sites

wget ‐‐http-user=labnol ‐‐http-password=hello123 http://ift.tt/1G9pBdT


16. Fetch pages that are behind a login page. You need to replace user and password with the actual form fields while the URL should point to the Form Submit (action) page.

wget ‐‐cookies=on ‐‐save-cookies cookies.txt ‐‐keep-session-cookies ‐‐post-data ‘user=labnol&password=123′ http://ift.tt/1mNFg9X

wget ‐‐cookies=on ‐‐load-cookies cookies.txt ‐‐keep-session-cookies http://ift.tt/1vIGglC


Retrieve File Details with wget


17. Find the size of a file without downloading it (look for Content Length in the response, the size is in bytes)

wget ‐‐spider ‐‐server-response http://ift.tt/1vIGg56


18. Download a file and display the content on screen without saving it locally.

wget ‐‐output-document – ‐‐quiet http://ift.tt/xD7Rux


wget


19. Know the last modified date of a web page (check the Last Modified tag in the HTTP header).

wget ‐‐server-response ‐‐spider http://www.labnol.org/


20. Check the links on your website to ensure that they are working. The spider option will not save the pages locally.

wget ‐‐output-file=logfile.txt ‐‐recursive ‐‐spider http://example.com


Also see: Essential Linux Commands


Wget – How to be nice to the server?


The wget tool is essentially a spider that scrapes / leeches web pages but some web hosts may block these spiders with the robots.txt files. Also, wget will not follow links on web pages that use the rel=nofollow attribute.


You can however force wget to ignore the robots.txt and the nofollow directives by adding the switch ‐‐execute robots=off to all your wget commands. If a web host is blocking wget requests by looking at the User Agent string, you can always fake that with the ‐‐user-agent=Mozilla switch.


The wget command will put additional strain on the site’s server because it will continuously traverse the links and download files. A good scraper would therefore limit the retrieval rate and also include a wait period between consecutive fetch requests to reduce the server load.


wget ‐‐limit-rate=20k ‐‐wait=60 ‐‐random-wait ‐‐mirror example.com


In the above example, we have limited the download bandwidth rate to 20 KB/s and the wget utility will wait anywhere between 30s and 90 seconds before retrieving the next resource.


Finally, a little quiz. What do you think this wget command will do?

wget ‐‐span-hosts ‐‐level=inf ‐‐recursive dmoz.org




The story, Spider a Website with Wget – 20 Practical Examples , was originally published at Digital Inspiration by Amit Agarwal on 09/12/2014 under Linux, Software.



via Digital Inspiration Technology Blog http://ift.tt/1yLcLR9