tell(3tcl) Tcl Built-In Commands tell(3tcl)
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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 re-
turned 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(3tcl), open(3tcl), close(3tcl), gets(3tcl), seek(3tcl), Tcl_Stan-
dardChannels(3tcl)
KEYWORDS
access position, channel, seeking
Tcl 8.1 tell(3tcl)
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