NAME¶
tell - Return current access position for an open channel
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