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'\"
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'\" Copyright (c) 1996 by 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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'\" RCS: @(#) $Id: GetStdChan.3,v 1.1.1.1 2002-01-16 10:25:24 markom Exp $
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'\"
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.so man.macros
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.TH Tcl_GetStdChannel 3 7.5 Tcl "Tcl Library Procedures"
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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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Tcl_GetStdChannel, Tcl_SetStdChannel \- procedures for retrieving and replacing the standard channels
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.SH SYNOPSIS
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.nf
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\fB#include \fR
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.sp
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Tcl_Channel
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\fBTcl_GetStdChannel\fR(\fItype\fR)
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.sp
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\fBTcl_SetStdChannel\fR(\fIchannel, type\fR)
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.sp
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.SH ARGUMENTS
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.AS Tcl_Channel channel in
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.AP int type in
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The identifier for the standard channel to retrieve or modify. Must be one of
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\fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, or \fBTCL_STDERR\fR.
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.AP Tcl_Channel channel in
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The channel to use as the new value for the specified standard channel.
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.BE
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.SH DESCRIPTION
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.PP
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Tcl defines three special channels that are used by various I/O related
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commands if no other channels are specified. The standard input channel
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has a channel name of \fBstdin\fR and is used by \fBread\fR and \fBgets\fR.
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The standard output channel is named \fBstdout\fR and is used by
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\fBputs\fR. The standard error channel is named \fBstderr\fR and is used for
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reporting errors. In addition, the standard channels are inherited by any
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child processes created using \fBexec\fR or \fBopen\fR in the absence of any
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other redirections.
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.PP
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The standard channels are actually aliases for other normal channels. The
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current channel associated with a standard channel can be retrieved by calling
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\fBTcl_GetStdChannel\fR with one of
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\fBTCL_STDIN\fR, \fBTCL_STDOUT\fR, or \fBTCL_STDERR\fR as the \fItype\fR. The
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return value will be a valid channel, or NULL.
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.PP
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A new channel can be set for the standard channel specified by \fItype\fR
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by calling \fBTcl_SetStdChannel\fR with a new channel or NULL in the
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\fIchannel\fR argument. If the specified channel is closed by a later call to
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\fBTcl_Close\fR, then the corresponding standard channel will automatically be
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set to NULL.
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.PP
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If \fBTcl_GetStdChannel\fR is called before \fBTcl_SetStdChannel\fR, Tcl will
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construct a new channel to wrap the appropriate platform-specific standard
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file handle. If \fBTcl_SetStdChannel\fR is called before
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\fBTcl_GetStdChannel\fR, then the default channel will not be created.
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.PP
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If one of the standard channels is set to NULL, either by calling
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\fBTcl_SetStdChannel\fR with a null \fIchannel\fR argument, or by calling
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\fBTcl_Close\fR on the channel, then the next call to \fBTcl_CreateChannel\fR
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will automatically set the standard channel with the newly created channel. If
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more than one standard channel is NULL, then the standard channels will be
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assigned starting with standard input, followed by standard output, with
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standard error being last.
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.SH "SEE ALSO"
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Tcl_Close(3), Tcl_CreateChannel(3)
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.SH KEYWORDS
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standard channel, standard input, standard output, standard error
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