| 1 | '\" |
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| 2 | '\" Copyright (c) 1993 The Regents of the University of California. |
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| 3 | '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. |
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| 4 | '\" |
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| 5 | '\" See the file "license.terms" for information on usage and redistribution |
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| 6 | '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
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| 7 | '\" |
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| 8 | '\" RCS: @(#) $Id: tell.n,v 1.9 2005/05/10 18:34:03 kennykb Exp $ |
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| 9 | '\" |
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| 10 | .so man.macros |
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| 11 | .TH tell n 8.1 Tcl "Tcl Built-In Commands" |
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| 12 | .BS |
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| 13 | '\" Note: do not modify the .SH NAME line immediately below! |
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| 14 | .SH NAME |
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| 15 | tell \- Return current access position for an open channel |
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| 16 | .SH SYNOPSIS |
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| 17 | \fBtell \fIchannelId\fR |
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| 18 | .BE |
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| 19 | |
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| 20 | .SH DESCRIPTION |
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| 21 | .PP |
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| 22 | Returns an integer string giving the current access position in |
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| 23 | \fIchannelId\fR. This value returned is a byte offset that can be passed to |
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| 24 | \fBseek\fR in order to set the channel to a particular position. Note |
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| 25 | that this value is in terms of bytes, not characters like \fBread\fR. |
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| 26 | The value returned is -1 for channels that do not support |
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| 27 | seeking. |
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| 28 | .PP |
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| 29 | \fIChannelId\fR must be an identifier for an open channel such as a |
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| 30 | Tcl standard channel (\fBstdin\fR, \fBstdout\fR, or \fBstderr\fR), |
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| 31 | the return value from an invocation of \fBopen\fR or \fBsocket\fR, or |
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| 32 | the result of a channel creation command provided by a Tcl extension. |
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| 33 | .SH EXAMPLE |
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| 34 | Read a line from a file channel only if it starts with \fBfoobar\fR: |
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| 35 | .CS |
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| 36 | # Save the offset in case we need to undo the read... |
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| 37 | set offset [\fBtell\fR $chan] |
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| 38 | if {[read $chan 6] eq "foobar"} { |
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| 39 | gets $chan line |
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| 40 | } else { |
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| 41 | set line {} |
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| 42 | # Undo the read... |
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| 43 | seek $chan $offset |
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| 44 | } |
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| 45 | .CE |
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| 46 | |
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| 47 | .SH "SEE ALSO" |
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| 48 | file(n), open(n), close(n), gets(n), seek(n), Tcl_StandardChannels(3) |
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| 49 | |
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| 50 | .SH KEYWORDS |
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| 51 | access position, channel, seeking |
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