NAME
       tell - Return current access position for an open channel

SYNOPSIS
       tell channelId


DESCRIPTION
       Returns  an  integer string giving the current access position in chan-
       nelId.  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 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.

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


KEYWORDS
