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'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH tell n 8.1 Tcl "Tcl Built-In Commands"
.so man.macros
.BS
'\" Note: do not modify the .SH NAME line immediately below!
.SH NAME
tell \- Return current access position for an open channel
.SH SYNOPSIS
\fBtell \fIchannelId\fR
.BE
.SH DESCRIPTION
.PP
Returns an integer giving the current access position in
\fIchannelId\fR. This value returned is a byte offset that can be passed to
\fBseek\fR in order to set the channel to a particular position. Note
that this value is in terms of bytes, not characters like \fBread\fR.
The value returned is -1 for channels that do not support
seeking.
.PP
\fIChannelId\fR must be an identifier for an open channel such as a
Tcl standard channel (\fBstdin\fR, \fBstdout\fR, or \fBstderr\fR),
the return value from an invocation of \fBopen\fR or \fBsocket\fR, or
the result of a channel creation command provided by a Tcl extension.
.SH EXAMPLE
.PP
Read a line from a file channel only if it starts with \fBfoobar\fR:
.PP
.CS
# Save the offset in case we need to undo the read...
set offset [\fBtell\fR $chan]
if {[read $chan 6] eq "foobar"} {
gets $chan line
} else {
set line {}
# Undo the read...
seek $chan $offset
}
.CE
.SH "SEE ALSO"
file(n), open(n), close(n), gets(n), seek(n), Tcl_StandardChannels(3)
.SH KEYWORDS
access position, channel, seeking
'\" Local Variables:
'\" mode: nroff
'\" fill-column: 78
'\" End:
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