[R] 404 HTTP not found

[Prof Brian Ripley]

See

?try
?tryCatch

On Mon, 18 Sep 2006, Stefan Th. Gries wrote:

> Hi
>
> I wrote a script which retrieves links from websites and loads them with scan:
>
> ...
> website<-tolower(scan(current.pages[i], what="character", sep="\n", quiet=TRUE))
> ...
>
> However occasionally, the script finds broken links, such as <http://www.google.com/test>. when the script tries to access such websites, the repeat loop breaks and I get the error message
>
> Error in file(file, "r") : unable to open connection
> In addition: Warning message:
> cannot open: HTTP status was '404 Not Found'
>
> Now my question: is there a way to test whether the target of a link exists that does not result in an error and, thus, discontinues my loop? I looked at the help files for files, scans, connections, and did a search for "404?' in th archives but couldn't find anything. I work with R 2.3.1 patched on Windows XP (both Home and Prof) and would appreciate any pointers ...
> Thanks a lot,
> STG

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595