tell(3tcl)

NAME

   tell - Return current access position for an open channel

SYNOPSIS

   tell channelId
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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

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