showConnections: Display Connections

Description

Display aspects of connections.

Usage

showConnections(all = FALSE)
getConnection(what)
closeAllConnections()
stdin()
stdout()
stderr()
nullfile()
isatty(con)

Arguments

all

logical: if true all connections, including closed ones and the standard ones are displayed. If false only open user-created connections are included.

what

integer: a row number of the table given by showConnections.

con

a connection.

Value

stdin(), stdout() and stderr() return connection objects.

showConnections returns a character matrix of information with a row for each connection, by default only for open non-standard connections.

getConnection returns a connection object, or NULL.

Details

stdin(), stdout() and stderr() are standard connections corresponding to input, output and error on the console respectively (and not necessarily to file streams). They are text-mode connections of class "terminal" which cannot be opened or closed, and are read-only, write-only and write-only respectively. The stdout() and stderr() connections can be re-directed by sink (and in some circumstances the output from stdout() can be split: see the help page).

The encoding for stdin() when redirected can be set by the command-line flag --encoding.

nullfile() returns filename of the null device ("/dev/null" on Unix, "nul:" on Windows).

showConnections returns a matrix of information. If a connection object has been lost or forgotten, getConnection will take a row number from the table and return a connection object for that connection, which can be used to close the connection, for example. However, if there is no R level object referring to the connection it will be closed automatically at the next garbage collection (except for gzcon connections).

closeAllConnections closes (and destroys) all user connections, restoring all sink diversions as it does so.

isatty returns true if the connection is one of the class "terminal" connections and it is apparently connected to a terminal, otherwise false. This may not be reliable in embedded applications, including GUI consoles.

Examples

Run this code

# NOT RUN {
showConnections(all = TRUE)
# }
# NOT RUN {
textConnection(letters)
# oops, I forgot to record that one
showConnections()
#  class     description      mode text   isopen   can read can write
#3 "letters" "textConnection" "r"  "text" "opened" "yes"    "no"
mycon <- getConnection(3)
# }
# NOT RUN {
c(isatty(stdin()), isatty(stdout()), isatty(stderr()))
# }