tell(3tcl) [debian man page]

tell(3tcl)						       Tcl Built-In Commands							tell(3tcl)

__________________________________________________________________________________________________________________________________________________

NAME

       tell - Return current access position for an open channel

SYNOPSIS

       tell channelId
_________________________________________________________________

DESCRIPTION

       Returns an integer string giving the current access position in channelId.  This value returned is a byte offset that can be passed to seek
       in order to set the channel to a particular position.  Note that this value is in terms of bytes, not  characters  like	read.	The  value
       returned is -1 for channels that do not support seeking.

       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.

EXAMPLE

       Read a line from a file channel only if it starts with foobar:
	      # Save the offset in case we need to undo the read...
	      set offset [tell $chan]
	      if {[read $chan 6] eq "foobar"} {
		  gets $chan line
	      } else {
		  set line {}
		  # Undo the read...
		  seek $chan $offset
	      }

SEE ALSO

       file(3tcl), open(3tcl), close(3tcl), gets(3tcl), seek(3tcl), Tcl_StandardChannels(3tcl)

KEYWORDS

       access position, channel, seeking

Tcl									8.1								tell(3tcl)

close(3tcl)						       Tcl Built-In Commands						       close(3tcl)

__________________________________________________________________________________________________________________________________________________

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 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  pipe-
       line 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

Tcl									7.5							       close(3tcl)