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