distrib/share/tcl/help/tcl/files/tell

   1 NAME
   2        tell - Return current access position for an open channel
   3
   4 SYNOPSIS
   5        tell channelId
   6
   7
   8 DESCRIPTION
   9        Returns  an  integer string giving the current access position in chan-
  10        nelId.  This value returned is a byte offset that can be passed to seek
  11        in  order  to set the channel to a particular position.  Note that this
  12        value is in terms of  bytes,  not  characters  like  read.   The  value
  13        returned is -1 for channels that do not support seeking.
  14
  15        ChannelId must be an identifier for an open channel such as a Tcl stan-
  16        dard channel (stdin, stdout, or stderr), the return value from an invo-
  17        cation  of  open or socket, or the result of a channel creation command
  18        provided by a Tcl extension.
  19
  20 EXAMPLE
  21        Read a line from a file channel only if it starts with foobar:
  22               # Save the offset in case we need to undo the read...
  23               set offset [tell $chan]
  24               if {[read $chan 6] eq "foobar"} {
  25                   gets $chan line
  26               } else {
  27                   set line {}
  28                   # Undo the read...
  29                   seek $chan $offset
  30               }
  31
  32
  33 SEE ALSO
  34        file(n), open(n), close(n), gets(n), seek(n), Tcl_StandardChannels(3)
  35
  36
  37 KEYWORDS