tell
tell
NAMESYNOPSIS
DESCRIPTION
EXAMPLE
SEE ALSO
KEYWORDS
___________________________
NAME
tell − Return current access position for an open channel
SYNOPSIS
tell channelId ___________________________
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(n), open(2), close(2), gets(3), seek(n), Tcl_StandardChannels(3)
KEYWORDS
access position, channel, seeking
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