\HeaderA{textConnection}{Text Connections}{textConnection}
\aliasA{textConnectionValue}{textConnection}{textConnectionValue}
\keyword{file}{textConnection}
\keyword{connection}{textConnection}
\begin{Description}\relax
Input and output text connections.
\end{Description}
\begin{Usage}
\begin{verbatim}
textConnection(object, open = "r", local = FALSE)

textConnectionValue(con)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{object}] character.  A description of the connection. 
For an input this is an \R{} character vector object, and for an output
connection the name for the \R{} character vector to receive the
output, or \code{NULL} (for none).

\item[\code{open}] character.  Either \code{"r"} (or equivalently \code{""})
for an input connection or \code{"w"} or \code{"a"} for an output
connection.
\item[\code{local}] logical.  Used only for output connections.  If \code{TRUE},
output is assigned to a variable in the calling environment.  Otherwise
the global environment is used.
\item[\code{con}] An output text connection.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
An input text connection is opened and the character vector is copied
at time the connection object is created, and \code{close}
destroys the copy.

An output text connection is opened and creates an \R{} character vector
of the given name in the user's workspace or in the calling environment,
depending on the value of the \code{local} argument.  This object will at all
times hold the completed lines of output to the connection, and
\code{\LinkA{isIncomplete}{isIncomplete}} will indicate if there is an incomplete
final line.  Closing the connection will output the final line,
complete or not.  (A line is complete once it has been terminated by
end-of-line, represented by \code{"\bsl{}n"} in \R.)  The output character
vector has locked bindings (see \code{\LinkA{lockBinding}{lockBinding}}) until
\code{close} is called on the connection.  The character vector can
also be retrieved \emph{via} \code{textConnectionValue}, which is the
only way to do so if \code{object = NULL}.

Opening a text connection with \code{mode = "a"} will attempt to
append to an existing character vector with the given name in the
user's workspace or the calling environment.  If none is found (even
if an object exists of the right name but the wrong type) a new
character vector will be created, with a warning.

You cannot \code{seek} on a text connection, and \code{seek} will
always return zero as the position.
\end{Details}
\begin{Value}
For \code{textConnection}, a connection object of class
\code{"textConnection"} which inherits from class \code{"connection"}.

For \code{textConnectionValue, a character vector.}
\end{Value}
\begin{Note}\relax
As output text connections keep the character vector up to date
line-by-line, they are relatively expensive to use, and it is often
better to use an anonymous \code{\LinkA{file}{file}()} connection to collect
output.

On platforms where \code{vsnprintf} does not return the needed length
of output (e.g., Windows) there is a 100,000 character limit on the
length of line for output connections: longer lines will be truncated
with a warning.
\end{Note}
\begin{References}\relax
Chambers, J. M. (1998)
\emph{Programming with Data. A Guide to the S Language.} Springer.\\{}
[S has input text conections only.]
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{connections}{connections}}, \code{\LinkA{showConnections}{showConnections}},
\code{\LinkA{pushBack}{pushBack}}, \code{\LinkA{capture.output}{capture.output}}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
zz <- textConnection(LETTERS)
readLines(zz, 2)
scan(zz, "", 4)
pushBack(c("aa", "bb"), zz)
scan(zz, "", 4)
close(zz)

zz <- textConnection("foo", "w")
writeLines(c("testit1", "testit2"), zz)
cat("testit3 ", file=zz)
isIncomplete(zz)
cat("testit4\n", file=zz)
isIncomplete(zz)
close(zz)
foo

## Not run: 
# capture R output: use part of example from help(lm)
zz <- textConnection("foo", "w")
ctl <- c(4.17, 5.58, 5.18, 6.11, 4.5, 4.61, 5.17, 4.53, 5.33, 5.14)
trt <- c(4.81, 4.17, 4.41, 3.59, 5.87, 3.83, 6.03, 4.89, 4.32, 4.69)
group <- gl(2, 10, 20, labels = c("Ctl", "Trt"))
weight <- c(ctl, trt)
sink(zz)
anova(lm.D9 <- lm(weight ~ group))
cat("\nSummary of Residuals:\n\n")
summary(resid(lm.D9))
sink()
close(zz)
cat(foo, sep = "\n")
## End(Not run)
\end{ExampleCode}
\end{Examples}

