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


       tell - Return current access position for an open channel

       tell channelId

       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.

       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

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

       access position, channel, seeking

Tcl                                    8.1                               tell(n)