Difference between revisions of "Wget"

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(Added section desctibing -m and related flags)
(Ignoring robots.txt)
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This will tell wget to not go up the directory tree, only downwards.
 
This will tell wget to not go up the directory tree, only downwards.
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== User-agents and robots.txt ==
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By default, wget plays nicely with a website's robots.txt. This can lead to situations where wget won't grab anything, since the robots.txt disallows wget.
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To avoid this: first, you should try using the --user-agent option:
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<pre>
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wget -mbc --user-agent="" http://website.com/
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</pre>
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This instructs wget to not send any user agent string at all. Another option for this is:
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<pre>
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wget -mbc -erobots=off http://website.com/
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</pre>
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...which tells wget to ignore robots.txt directives altogether.
  
 
== Tricks and Traps ==
 
== Tricks and Traps ==

Revision as of 15:32, 7 January 2009

GNU Wget is a free utility for non-interactive download of files from the Web. Using wget, it is possible to grab a large chunk of data, or mirror an entire website with complete directory tree, with a single command. In the tool belt of the renegade archivist, Wget tends to get an awful lot of use. (Note: Some people prefer to use cURL)

This guide will not attempt to explain all possible uses of wget; rather, this is intended to be a concise intro to using wget, specifically geared towards using the tool to archive data such as podcasts, pdfs, or entire websites. Issues such as using wget to circumvent user-agent checks, or robots.txt restrictions, will be outlined as well.

Mirroring a website

When you run something like this:

wget http://icanhascheezburger.com/

...wget will just grab the first page it hits, usually something like index.html. If you give it the -m flag:

wget -m http://icanhascheezburger.com/

...then wget will happily slurp down anything within reach of its greedy claws, putting files in a complete directory structure. Go make a sandwich or something.

You'll probably want to pair -m with -c (which tells wget to continue partially-complete downloads) and -b (which tells wget to fork to the background, logging to wget-log).

If you want to grab everything in a specific directory - say, the SICP directory on the mitpress web site - use the -np flag:

wget -mbc -np http://mitpress.mit.edu/sicp

This will tell wget to not go up the directory tree, only downwards.

User-agents and robots.txt

By default, wget plays nicely with a website's robots.txt. This can lead to situations where wget won't grab anything, since the robots.txt disallows wget.

To avoid this: first, you should try using the --user-agent option:

wget -mbc --user-agent="" http://website.com/

This instructs wget to not send any user agent string at all. Another option for this is:

wget -mbc -erobots=off http://website.com/

...which tells wget to ignore robots.txt directives altogether.

Tricks and Traps

  • A standard methodology to prevent scraping of websites is to block access via user agent string. Wget is a good web citizen and identifies itself. Renegard archivists are not good web citizens in this sense. The --user-agent option will allow you to act like something else.
  • Some websites are actually aggregates of multiple machines and subdomains, working together. (For example, a site called dyingwebsite.com will have additional machines like download.dyingwebsite.com or mp3.dyingwebsite.com) To account for this, add the following options: -H -Ddomain.com

Essays and Reading on the Use of WGET