\HeaderA{readLines}{Read Text Lines from a Connection}{readLines}
\keyword{file}{readLines}
\keyword{connection}{readLines}
\begin{Description}\relax
Read text lines from a connection.
\end{Description}
\begin{Usage}
\begin{verbatim}
readLines(con = stdin(), n = -1, ok = TRUE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{con}] A connection object or a character string.
\item[\code{n}] integer.  The (maximal) number of lines to
read. Negative values indicate that one should read up to the end of
the connection.
\item[\code{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.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
If the \code{con} is a character string, the function call
\code{\LinkA{file}{file}} to obtain a file connection which is opened for
the duration of the function call.

If the connection is open it is read from its current position.
If it is not open, it is opened 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 blocking
text-mode connection (or a non-text-mode connection) the line
will be accepted, with a warning.  For a non-blocking text-mode
connection the incomplete line is pushed back, silently.

Whatever mode the connection is opened in, any of LF, CRLF or CR will
be accepted as the EOL marker for a line.
\end{Details}
\begin{Value}
A character vector of length the number of lines read.
\end{Value}
\begin{SeeAlso}\relax
\code{\LinkA{connections}{connections}}, \code{\LinkA{writeLines}{writeLines}}, \code{\LinkA{readBin}{readBin}},
\code{\LinkA{scan}{scan}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
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
\end{ExampleCode}
\end{Examples}

