close(3tcl)

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
   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.)

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(3tcl),        open(3tcl),         socket(3tcl),         eof(3tcl),
   Tcl_StandardChannels(3tcl)

KEYWORDS

   blocking, channel, close, nonblocking

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