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\name{pushBack}
\alias{pushBack}
\alias{pushBackLength}
\title{Push Text Back on to a Connection}
\description{
  Functions to push back text lines onto a connection, and to enquire
  how many lines are currently pushed back.
}
\usage{
pushBack(data, connection, newLine = TRUE)
pushBackLength(connection)
}
\arguments{
  \item{data}{a character vector.}
  \item{connection}{A connection.}
  \item{newLine}{logical. If true, a newline is appended to each string
    pushed back.}
}
\details{
  Several character strings can be pushed back on one or more occasions.
  The occasions form a stack, so the first line to be retrieved will be
  the first string from the last call to \code{pushBack}.  Lines which
  are pushed back are read prior to the normal input from the
  connection, by the normal text-reading functions such as
  \code{\link{readLines}} and \code{\link{scan}}.

  Pushback is only allowed for readable connections.
}
\value{
  \code{pushBack} returns nothing.

  \code{pushBackLength} returns number of lines currently pushed back.
}
\seealso{\code{\link{connections}}, \code{\link{readLines}}.}

\examples{
zz <- textConnection(LETTERS)
readLines(zz, 2)
pushBack(c("aa", "bb"), zz)
pushBackLength(zz)
readLines(zz, 1)
pushBackLength(zz)
readLines(zz, 1)
readLines(zz, 1)
close(zz)
}
\keyword{connection}