/usr/gnu/man/cat.n/tell.n.Z(/usr/gnu/man/cat.n/tell.n.Z)

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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 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

       access position, channel, seeking

Tcl                                   8.1                              tell(n)