Question

I would like to know how can I check if a html is available. If it is not, I would like to control the return to avoid stop the script by error.
Ex:

arq <- readLines("www.pageerror.com.br")
print(arq)

Answer 1

An alternative is try() – it is simpler to work with than trycatch() but isn’t as featureful. You might also need to suppress warnings as R will report that it can’t resolve the address.

You want something like this in your script:

URL <- "http://www.pageerror.com.br"
arq <- try(suppressWarnings(readLines(con <- url(URL))), silent = TRUE)
close(con) ## close the connection
if(inherits(arq, "try-error")) {
    writeLines(strwrap(paste("Page", URL, "is not available")))
} else {
    print(arq)
}

The silent = TRUE bit suppresses the reporting of errors (if you leave this at the default FALSE, then R will report the error but not abort the script). We wrap the potentially error-raising function call in try(...., silent = TRUE), with suppressWarnings() being used to suppress the warnings. Then we test the class of the returned object arq and if it inherits from class "try-error" we know the page could not be retrieved and issue a message indicating so. Otherwise we can print arq.