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% File src/library/base/man/readLines.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2014 R Core Team
% Distributed under GPL 2 or later

\name{readLines}
\alias{readLines}
\title{Read Text Lines from a Connection}
\description{
  Read some or all text lines from a connection.
}
\usage{
readLines(con = stdin(), n = -1L, ok = TRUE, warn = TRUE,
          encoding = "unknown", skipNul = FALSE)
}
\arguments{
  \item{con}{a \link{connection} object or a character string.}
  \item{n}{integer.  The (maximal) number of lines to
    read.  Negative values indicate that one should read up to the end of
    input on the connection.}
  \item{ok}{logical.  Is it OK to reach the end of the connection before
    \code{n > 0} lines are read?  If not, an error will be generated.}
  \item{warn}{logical.  Warn if a text file is missing a final EOL or if
    there are embedded nuls in the file.}
  \item{encoding}{encoding to be assumed for input strings.  It is
    used to mark character strings as known to be in
    Latin-1 or UTF-8: it is not used to re-encode the input.  To do the
    latter, specify the encoding as part of the connection \code{con} or
    via \code{\link{options}(encoding=)}: see the examples.
#ifdef windows
    See also \sQuote{Details}.
#endif
  }
  \item{skipNul}{logical: should nuls be skipped?}
}
\details{
  If the \code{con} is a character string, the function calls
  \code{\link{file}} to obtain a file connection which is opened for
  the duration of the function call.  This can be a compressed file.

  If the connection is open it is read from its current position.  If it
  is not open, it is opened in \code{"rt"} mode for the duration of
  the call and then closed again.

  If the final line is incomplete (no final EOL marker) the behaviour
  depends on whether the connection is blocking or not.  For a
  non-blocking text-mode connection the incomplete line is pushed back,
  silently.  For all other connections the line will be accepted, with a
  warning.

  Whatever mode the connection is opened in, any of LF, CRLF or CR will
  be accepted as the EOL marker for a line.

  Embedded nuls in the input stream will terminate the line currently
  being read, with a warning (unless \code{skipNul = TRUE} or \code{warn
    = FALSE)}).
  
  If \code{con} is a not-already-open \link{connection} with a non-default
  \code{encoding} argument, the text is converted to UTF-8 and declared
  as such (and the \code{encoding} argument to \code{readLines} is ignored).
  See the examples.
}
\value{
  A character vector of length the number of lines read.

  The elements of the result have a declared encoding if \code{encoding} is
  \code{"latin1"} or \code{"UTF-8"},
}
\note{
  The default connection, \code{\link{stdin}}, may be different from
  \code{con = "stdin"}: see \code{\link{file}}.
}
\seealso{
  \code{\link{connections}}, \code{\link{writeLines}}, \code{\link{readBin}},
  \code{\link{scan}}}

\examples{
cat("TITLE extra line", "2 3 5 7", "", "11 13 17", file = "ex.data",
    sep = "\n")
readLines("ex.data", n = -1)
unlink("ex.data") # tidy up

## difference in blocking
cat("123\nabc", file = "test1")
readLines("test1") # line with a warning

con <- file("test1", "r", blocking = FALSE)
readLines(con) # empty
cat(" def\n", file = "test1", append = TRUE)
readLines(con) # gets both
close(con)

unlink("test1") # tidy up

\dontrun{
# read a 'Windows Unicode' file
A <- readLines(con <- file("Unicode.txt", encoding = "UCS-2LE"))
close(con)
unique(Encoding(A)) # will most likely be UTF-8
}}
\keyword{file}
\keyword{connection}