tell(n) Tcl Built-In Commands tell(n)
NAME
tell - Return current access position for an open channel
SYNOPSIS
tell channelId
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)
tcl 8.6.0 - Generated Sat Jan 12 15:50:22 CST 2013