** Summary ** Web scraping is the practice of getting information from a web page and reformatting it. ** Description ** [[clt postings from jooky and [David Welton] and [Larry Virden].]] When a service API is not available, sometimes the only recourse is to scrape a web interface instead. An alternative to is to work with the web host to work out details of a [Web Service] that would provide useful information programatically. Web scraping is often employed for small tasks where an API, such as sendi updates to a pager/WAP phone, etc., emailing one's personal account status to an account, or moving data from a website into a local database. See projects like http://sitescooper.org/ , http://www.plkr.org/ , or [Python]-based mechanize [http://wwwsearch.sourceforge.net/mechanize/] (itself a descendant of Andy Lester's '''WWW::Mechanize''' for [Perl]) for non-[Tcl] tools for scraping the web. "Web Scraping ..." [http://cedar.intel.com/cgi-bin/ids.dll/content/content.jsp?cntKey=Generic+Editorial%3a%3aws_scraping&cntType=IDS_EDITORIAL&cat=CJA] (URL not 404 - instead links to a generic landing page on Aug 28, 2011) ** Etiquette ** [NEM] notes that to be a good web-citizen any web robots should follow some guidelines: * set the user-agent to some unique identifier for your program and include some contact details (email, website) so that site admins can contact you if they have any issues (you can do this with http::config -useragent); * fetch the /robots.txt file from the server you are scraping and check every URL accessed against it (see [http://www.robotstxt.org/]). (probably more - feel free to expand this list). Checking the robots.txt is relatively simple but still requires a bit of effort. As I'm currently doing some web-scraping I may package up the code I'm using for this into a webrobot package. ** Examples ** [Downloading your utility usage from Pacific Gas and Electric using TCL]: [Downloading pictures from Flickr]: [A little rain forecaster] : [An HTTP Robot in Tcl]: [Web2Desktop]: [tcllib]/examples/oscon: which uses the [htmlparse] module (among others) to parse the schedule pages for OSCON 2001 and convert them into [CSV] files usable by [Excel] and other applications. [LemonTree branch] uses this technique.: tDOM's HTML-parser + XPath expression: web scraping example for EBAY, presented at the [First European Tcl/Tk Users Meeting] ( http://sdf.lonestar.org/~loewerj/tdom2001.ppt and http://www.tu-harburg.de/skf/tcltk/tclum2001.pdf.gz) [TcLeo]: allows querying the English <=> German web dictionary at http://dict.leo.org from the command line. [ucnetgrab]: [Getting stock quotes over the internet]: [TaeglicherStrahlungsBericht]: Daily updated radiation map of german government's (BfS) sensor installations [wiki-reaper] (and [wish-reaper]): [tinyurl]: [Amazon.de PreOrder]: [LV] This isn't technically web scraping, but I'm uncertain where else to reference it - it is making use of a web site's cgi functionality, from a Tk application, from what I can tell [Synchronizing System Time]: [googling with SOAP] [Daily Dilbert]: ** Tools ** [htmlparse]: [tclwebtest]: a tool to write automated tests for web applications [TWiG]: a tool for extracting blocks of data from pages retrieved from the web [Getleft]: [pop3line]: fetches e-mails from the web-mailer of T-Online. [A little RSS reaper]: [RS]: loads an RSS page, renders it to HTML, plus it compacts the referenced pages into the same document with local links, while trying to avoid ads and noise. Not perfect, but I use it daily to reap news sites onto my iPaq :) [LemonTree branch]: a GUI to browse an HTML document [grabchat]: a tool to grab yesterday's tcler's wiki chat room log [AutoIt]: a simple tool to simulate key presses, mouse movements, and window commands ** Non-Tcl Tools ** [http://www.crummy.com/software/BeautifulSoup/%|%Beautiful Soup%|%]: A web scraping library for Python [http://addons.mozilla.org/en-US/firefox/addon/imacros-for-firefox/%|%iMacros for Firefox%|%] [http://www.mozilla.org/js/spidermonkey/%|%spidermonkey%|%]: which Kaitzschu has suggested deserves Tcl [binding]s. ** See Also ** [screenscrape]: [websearch]: [TkChat]: is one Tk/Tcl web scraper for this web site's chat room! [lapecheronza]: monitor your favorite websites for updates and changes. [http://www.vogel-nest.de/wiki/Main/WebScraping1%|%Tutorial for Web scraping with regexp and tdom%|%] [web crawler]: ** Resources ** * [http://www.unixreview.com/documents/s=7822/ur0302h/%|%Web scraping is easy%|%] (URL is 404 on Aug 28, 2011) * Apt comments on the technical and business difficulty of Web scraping, along with mentions of WebL and NQL, appear here [http://lambda.weblogs.com/discuss/msgReader$3567]. * [Perl] probably has the most current Web-scraping activity (even more than tclwebtest?), especially with [http://www.perl.com/pub/a/2003/01/22/mechanize.html%|%WWW::Mechanize%|%], although [http://www.unixreview.com/documents/s=1820/uni1011713175619/0201i.htm%|%Curl%|%] also has its place. * In 2004, WWWGrab [http://www.wwwgrab.com/] looks interesting for those in a position to work under [Windows]. [http://lbrandy.com/blog/2009/08/an-almost-perfect-hack/%|%An almost perfect real-world hack]: in which Louis Brandy describes using Python and iMacros to do some web scraping ** Example by Ian, 2007, comp.lang.tcl ** [LV] 2007-11-01: On comp.lang.tcl, during Oct 31, 2007, in a thread [http://groups.google.com/group/comp.lang.tcl/browse_thread/thread/0d2d015491a231bc/75a399da09ae569f#75a399da09ae569f] about someone wanting to extract data from an html page, a user by the name of Ian posted the following snippet of code as an example of what they do to deal with a page of html that has some data in it that ====== package require htmlparse package require struct proc html2data s { ::struct::tree x ::htmlparse::2tree $s x ::htmlparse::removeVisualFluff x set data [list] x walk root q { if {([x get $q type] eq "PCDATA") && [string match R\u00e6kke/pulje [x get $q data]]} { set p $q for {set i 3} {$i} {incr i -1} {set p [x parent $p]} foreach {row} [lrange [x children $p] 1 end] { ...... } break } } return $data } ====== [LemonTree branch] uses this technique. ** Misc ** [[It seems many of us do our own "home-grown" solutions for these needs.]] Also, some web hosts provide [XML] versions ([RSS]), or specially formatted versions for use with Avantgo or the plucker command, with the goal of aiding people who need some sort of specialized format for small devices, etc. It would be great if someone making legitimate use of some of these sources would share some of their code to do this sort of thing. <> Internet | Web