Closes the channel given by channelId.
ChannelId must be an identifier for an open channel such as a
Tcl standard channel (stdin, stdout, or stderr),
the return value from an invocation of open or socket, or
the result of a channel creation command provided by a Tcl extension.
All buffered output is flushed to the channels output device,
any buffered input is discarded, the underlying file or device is closed,
and channelId becomes unavailable for use.
If the channel is blocking, the command does not return until all output
If the channel is nonblocking and there is unflushed output, the
channel remains open and the command
returns immediately; output will be flushed in the background and the
channel will be closed when all the flushing is complete.
If channelId is a blocking channel for a command pipeline then
close waits for the child processes to complete.
If the channel is shared between interpreters, then close
makes channelId unavailable in the invoking interpreter but has no
other effect until all of the sharing interpreters have closed the
When the last interpreter in which the channel is registered invokes
close, the cleanup actions described above occur. See the
interp command for a description of channel sharing.
Channels are automatically closed when an interpreter is destroyed and
when the process exits. Channels are switched to blocking mode, to ensure
that all output is correctly flushed before the process exits.
The command returns an empty string, and may generate an error if
an error occurs while flushing output. If a command in a command
pipeline created with open returns an error, close
generates an error (similar to the exec command.)