close(n)

______________________________________________________________________________

NAME

       close - Close an open channel.

SYNOPSIS

       close channelId
_________________________________________________________________

DESCRIPTION

       Closes the channel given by channelId.

       ChannelId must be an identifier for an open channel such as a Tcl stan- |
       dard channel (stdin, stdout, or stderr), the return value from an invo- |
       cation  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  out- |
       put  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 chan- |
       nelId 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.)

EXAMPLE

       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
              }

SEE ALSO

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

KEYWORDS

       blocking, channel, close, nonblocking

Tcl                                   7.5                             close(n)