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



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NAME
       close - Close an open channel

SYNOPSIS
       close channelId
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DESCRIPTION
       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 imme-diately; immediately;
       diately; output will be flushed in the background and the channel will be closed when all the  flush-ing flushing
       ing 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.  Chan-nels Channels
       nels 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 out-put. output.
       put.  If a command in a command pipeline created with open returns an error, close generates an error
       (similar to the exec command.)

EXAMPLE
       This  illustrates how you can use Tcl to ensure that files get closed even when errors happen by com-bining combining
       bining 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
              }


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


KEYWORDS
       blocking, channel, close, nonblocking



Tcl                                                  7.5                                            close(n)