Provided by: tcl8.6-doc_8.6.9+dfsg-2_all bug

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