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OpenSolaris 2009.06 - man page for tell (opensolaris section 1t)

tell(1T)						       Tcl Built-In Commands							  tell(1T)


tell - Return current access position for an open channel
tell channelId _________________________________________________________________
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.
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 }
file(1T), open(1T), close(1T), gets(1T), seek(1T), Tcl_StandardChannels(3TCL)
access position, channel, seeking
See attributes(5) for descriptions of the following attributes: +--------------------+-----------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +--------------------+-----------------+ |Availability | SUNWTcl | +--------------------+-----------------+ |Interface Stability | Uncommitted | +--------------------+-----------------+
Source for Tcl is available on Tcl 8.1 tell(1T)