close(n) Tcl Built-In Commands close(n) 







close - Close an open channel








close channelId












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 channel's 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 is flushed. 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 channel.
    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.)








This illustrates how you can use Tcl to ensure that files get
    closed even when errors happen by combining catch, close and
    return:




proc withOpenFile {filename channelVar script} {
    upvar 1 $channelVar chan
    set chan [open $filename]
    catch {
        uplevel 1 $script
    } result options
    close $chan
    return -options $options $result
}












file(n), open(n), socket(n), eof(n), Tcl_StandardChannels(3)










blocking, channel, close, nonblocking







  

    7.5
    Tcl