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\name{url.exists}
\alias{url.exists}
\title{Check if URL exists}
\description{
This functions is analogous to \code{\link[base]{file.exists}}
and determines whether a request for a specific URL responds
without error. We make the request but ask the server
not to return the body. We just process the header.
}
\usage{
url.exists(url, ..., .opts = list(...),
curl = getCurlHandle(.opts = .opts),
.header = FALSE)
}
\arguments{
\item{url}{the URL whose existence we are to test}
\item{\dots}{name = value pairs of Curl options.}
\item{.opts}{a list of name = value pairs of Curl options.}
\item{curl}{a Curl handle that the caller can specify if she wants to
reuse an existing handle, e.g. with different options already
specified or that has previously established a connection to the Web
server}
\item{.header}{a logical value that if \code{TRUE} causes the header
information to be returned.
}
}
\details{
This makes an HTTP request but with the nobody option set to
\code{FALSE} so that we don't actually retrieve the contents of the URL.
}
\value{
If \code{.header} is \code{FALSE}, this returns
\code{TRUE} or \code{FALSE} indicating whether
the request was successful (had a status with a value
in the 200 range).
If \code{.header} is \code{TRUE}
}
\references{
HTTP specification
}
\author{
Duncan Temple Lang
}
\seealso{
\code{\link{curlPerform}}
}
\examples{
url.exists("http://www.omegahat.net/RCurl")
try(url.exists("http://www.omegahat.net/RCurl-xxx"))
}
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