Tcl Built-In Commands                                   close(1T)





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  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  dev-
     ice, 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 descrip-  
     tion 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 com-
     mand in a command pipeline  created  with  open  returns  an
     error,  close  generates  an error (similar to the exec com-
     mand.)




Tcl                     Last change: 7.5                        1






Tcl Built-In Commands                                   close(1T)



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(1T),       open(1T),        socket(1T),        eof(1T),
     TclStandardChannels(3TCL)


KEYWORDS
     blocking, channel, close, nonblocking

ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:

     
       ATRIBUTE TYPE     ATRIBUTE VALUE
    
     Availability         SUNWTcl        
    
     Interface Stability  Uncommitted    
    

NOTES
     Source for Tcl is available on http:/opensolaris.org.


















Tcl                     Last change: 7.5                        2