[OpenSPARC-T2-DV] / tools / src / nas,5.n2.os.2 / lib / python / man / man3 / Tcl_StandardChannels.3

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'\" The definitions below are for supplemental macros used in Tcl/Tk
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'\"	name are examples of largest possible arguments that will be passed
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'\" .OP cmdName dbName dbClass
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See the \\fBoptions\\fR manual entry for details on the standard options.
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.TH "Standard Channels" 3 7.5 Tcl "Tcl Library Procedures"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
Tcl_StandardChannels \- How the Tcl library deals with the standard channels
.BE

.SH DESCRIPTION
.PP
This page explains the initialization and use of standard channels in
the Tcl library.
.PP
The term \fIstandard channels\fR comes out of the Unix world and
refers to the three channels automatically opened by the OS for
each new application. They are \fBstdin\fR, \fBstdout\fR and
\fBstderr\fR. The first is the standard input an application can read
from, the other two refer to writable channels, one for regular
output and the other for error messages.
.PP
Tcl generalizes this concept in a cross-platform way and
exposes standard channels to the script level.

.SH APIs
.PP
The public API procedures dealing directly with standard channels are
\fBTcl_GetStdChannel\fR and \fBTcl_SetStdChannel\fR. Additional public
APIs to consider are \fBTcl_RegisterChannel\fR,
\fBTcl_CreateChannel\fR and \fBTcl_GetChannel\fR.
.SH "INITIALIZATION OF TCL STANDARD CHANNELS"
.PP
Standard channels are initialized by the Tcl library in three cases:
when explicitly requested, when implicitly required before returning
channel information, or when implicitly required during registration
of a new channel.
.PP
These cases differ in how they handle unavailable platform- specific
standard channels.  (A channel is not ``available'' if it could not be
successfully opened; for example, in a Tcl application run as a
Windows NT service.)
.TP
1)
A single standard channel is initialized when it is explicitly
specified in a call to \fBTcl_SetStdChannel\fR.  The state of the
other standard channels are unaffected.
.sp
Missing platform-specific standard channels do not matter here. This
approach is not available at the script level.
.TP
2)
All uninitialized standard channels are initialized to
platform-specific default values:
.RS
.TP
(a)
when open channels are listed with \fBTcl_GetChannelNames\fR (or the
\fBfile channels\fR script command), or
.TP
(b)
when information about any standard channel is requested with a call
to \fBTcl_GetStdChannel\fR, or with a call to \fBTcl_GetChannel\fR
which specifies one of the standard names (\fBstdin\fR, \fBstdout\fR
and \fBstderr\fR).
.RE
.sp
.RS
In case of missing platform-specific standard channels, the Tcl
standard channels are considered as initialized and then immediately
closed. This means that the first three Tcl channels then opened by
the application are designated as the Tcl standard channels.
.RE
.TP
3)
All uninitialized standard channels are initialized to
platform-specific default values when a user-requested channel is
registered with \fBTcl_RegisterChannel\fR.
.sp
In case of unavailable platform-specific standard channels the channel
whose creation caused the initialization of the Tcl standard channels
is made a normal channel.  The next three Tcl channels opened by the
application are designated as the Tcl standard channels.  In other
words, of the first four Tcl channels opened by the application the
second to fourth are designated as the Tcl standard channels.
.PP
.SH "RE-INITIALIZATION OF TCL STANDARD CHANNELS"
.PP
Once a Tcl standard channel is initialized through one of the methods
above, closing this Tcl standard channel will cause the next call to
\fBTcl_CreateChannel\fR to make the new channel the new standard
channel, too. If more than one Tcl standard channel was closed
\fBTcl_CreateChannel\fR will fill the empty slots in the order
\fBstdin\fR, \fBstdout\fR and \fBstderr\fR.
.PP
\fBTcl_CreateChannel\fR will not try to reinitialize an empty slot if
that slot was not initialized before. It is this behavior which
enables an application to employ method 1 of initialization, i.e. to
create and designate their own Tcl standard channels.

.SH tclsh
.PP
The Tcl shell (or rather \fBTcl_Main\fR) uses method 2 to initialize
the standard channels.

.SH wish
.PP
The windowing shell (or rather \fBTk_MainEx\fR) uses method 1 to
initialize the standard channels (See \fBTk_InitConsoleChannels\fR)
on non-Unix platforms.  On Unix platforms, \fBTk_MainEx\fR implicitly
uses method 2 to initialize the standard channels.

.SH "SEE ALSO"
Tcl_CreateChannel(3), Tcl_RegisterChannel(3), Tcl_GetChannel(3), Tcl_GetStdChannel(3), Tcl_SetStdChannel(3), Tk_InitConsoleChannels(3), tclsh(1), wish(1), Tcl_Main(3), Tk_MainEx(3)

.SH KEYWORDS
standard channels
Commit	Line	Data
86530b38 AT	1	'\"
	2	'\" Copyright (c) 2001 by ActiveState Corporation
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	5	'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
	6	'\"
	7	'\" RCS: @(#) $Id: StdChannels.3,v 1.8 2002/11/15 15:34:17 dkf Exp $
	8	'\"
	9	'\" The definitions below are for supplemental macros used in Tcl/Tk
	10	'\" manual entries.
	11	'\"
	12	'\" .AP type name in/out ?indent?
	13	'\" Start paragraph describing an argument to a library procedure.
	14	'\" type is type of argument (int, etc.), in/out is either "in", "out",
	15	'\" or "in/out" to describe whether procedure reads or modifies arg,
	16	'\" and indent is equivalent to second arg of .IP (shouldn't ever be
	17	'\" needed; use .AS below instead)
	18	'\"
	19	'\" .AS ?type? ?name?
	20	'\" Give maximum sizes of arguments for setting tab stops. Type and
	21	'\" name are examples of largest possible arguments that will be passed
	22	'\" to .AP later. If args are omitted, default tab stops are used.
	23	'\"
	24	'\" .BS
	25	'\" Start box enclosure. From here until next .BE, everything will be
	26	'\" enclosed in one large box.
	27	'\"
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	31	'\" .CS
	32	'\" Begin code excerpt.
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	36	'\"
	37	'\" .VS ?version? ?br?
	38	'\" Begin vertical sidebar, for use in marking newly-changed parts
	39	'\" of man pages. The first argument is ignored and used for recording
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	41	'\" found and removed when they reach a certain age. If another argument
	42	'\" is present, then a line break is forced before starting the sidebar.
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	52	'\"
	53	'\" .SO
	54	'\" Start of list of standard options for a Tk widget. The
	55	'\" options follow on successive lines, in four columns separated
	56	'\" by tabs.
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	59	'\" End of list of standard options for a Tk widget.
	60	'\"
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	62	'\" Start of description of a specific option. cmdName gives the
	63	'\" option's name as specified in the class command, dbName gives
	64	'\" the option's name in the option database, and dbClass gives
65	'\" the option's class in the option database.
66	'\"
67	'\" .UL arg1 arg2
68	'\" Print arg1 underlined, then print arg2 normally.
69	'\"
70	'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
71	'\"
72	'\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
73	.if t .wh -1.3i ^B
74	.nr ^l \n(.l
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78	.ie !"\\$4"" .TP \\$4
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204	..
205	'\" # SO - start of list of standard options
206	.de SO
207	.SH "STANDARD OPTIONS"
208	.LP
209	.nf
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212	..
213	'\" # SE - end of list of standard options
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218	See the \\fBoptions\\fR manual entry for details on the standard options.
219	..
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227	Database Class: \\fB\\$3\\fR
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241	..
242	.de UL
243	\\$1\l'\|0\(ul'\\$2
244	..
245	.TH "Standard Channels" 3 7.5 Tcl "Tcl Library Procedures"
246	.BS
247	'\" Note: do not modify the .SH NAME line immediately below!
248	.SH NAME
249	Tcl_StandardChannels \- How the Tcl library deals with the standard channels
250	.BE
251
252	.SH DESCRIPTION
253	.PP
254	This page explains the initialization and use of standard channels in
255	the Tcl library.
256	.PP
257	The term \fIstandard channels\fR comes out of the Unix world and
258	refers to the three channels automatically opened by the OS for
259	each new application. They are \fBstdin\fR, \fBstdout\fR and
260	\fBstderr\fR. The first is the standard input an application can read
261	from, the other two refer to writable channels, one for regular
262	output and the other for error messages.
263	.PP
264	Tcl generalizes this concept in a cross-platform way and
265	exposes standard channels to the script level.
266
267	.SH APIs
268	.PP
269	The public API procedures dealing directly with standard channels are
270	\fBTcl_GetStdChannel\fR and \fBTcl_SetStdChannel\fR. Additional public
271	APIs to consider are \fBTcl_RegisterChannel\fR,
272	\fBTcl_CreateChannel\fR and \fBTcl_GetChannel\fR.
273	.SH "INITIALIZATION OF TCL STANDARD CHANNELS"
274	.PP
275	Standard channels are initialized by the Tcl library in three cases:
276	when explicitly requested, when implicitly required before returning
277	channel information, or when implicitly required during registration
278	of a new channel.
279	.PP
280	These cases differ in how they handle unavailable platform- specific
281	standard channels. (A channel is not ``available'' if it could not be
282	successfully opened; for example, in a Tcl application run as a
283	Windows NT service.)
284	.TP
285	1)
286	A single standard channel is initialized when it is explicitly
287	specified in a call to \fBTcl_SetStdChannel\fR. The state of the
288	other standard channels are unaffected.
289	.sp
290	Missing platform-specific standard channels do not matter here. This
291	approach is not available at the script level.
292	.TP
293	2)
294	All uninitialized standard channels are initialized to
295	platform-specific default values:
296	.RS
297	.TP
298	(a)
299	when open channels are listed with \fBTcl_GetChannelNames\fR (or the
300	\fBfile channels\fR script command), or
301	.TP
302	(b)
303	when information about any standard channel is requested with a call
304	to \fBTcl_GetStdChannel\fR, or with a call to \fBTcl_GetChannel\fR
305	which specifies one of the standard names (\fBstdin\fR, \fBstdout\fR
306	and \fBstderr\fR).
307	.RE
308	.sp
309	.RS
310	In case of missing platform-specific standard channels, the Tcl
311	standard channels are considered as initialized and then immediately
312	closed. This means that the first three Tcl channels then opened by
313	the application are designated as the Tcl standard channels.
314	.RE
315	.TP
316	3)
317	All uninitialized standard channels are initialized to
318	platform-specific default values when a user-requested channel is
319	registered with \fBTcl_RegisterChannel\fR.
320	.sp
321	In case of unavailable platform-specific standard channels the channel
322	whose creation caused the initialization of the Tcl standard channels
323	is made a normal channel. The next three Tcl channels opened by the
324	application are designated as the Tcl standard channels. In other
325	words, of the first four Tcl channels opened by the application the
326	second to fourth are designated as the Tcl standard channels.
327	.PP
328	.SH "RE-INITIALIZATION OF TCL STANDARD CHANNELS"
329	.PP
330	Once a Tcl standard channel is initialized through one of the methods
331	above, closing this Tcl standard channel will cause the next call to
332	\fBTcl_CreateChannel\fR to make the new channel the new standard
333	channel, too. If more than one Tcl standard channel was closed
334	\fBTcl_CreateChannel\fR will fill the empty slots in the order
335	\fBstdin\fR, \fBstdout\fR and \fBstderr\fR.
336	.PP
337	\fBTcl_CreateChannel\fR will not try to reinitialize an empty slot if
338	that slot was not initialized before. It is this behavior which
339	enables an application to employ method 1 of initialization, i.e. to
340	create and designate their own Tcl standard channels.
341
342	.SH tclsh
343	.PP
344	The Tcl shell (or rather \fBTcl_Main\fR) uses method 2 to initialize
345	the standard channels.
346
347	.SH wish
348	.PP
349	The windowing shell (or rather \fBTk_MainEx\fR) uses method 1 to
350	initialize the standard channels (See \fBTk_InitConsoleChannels\fR)
351	on non-Unix platforms. On Unix platforms, \fBTk_MainEx\fR implicitly
352	uses method 2 to initialize the standard channels.
353
354	.SH "SEE ALSO"
355	Tcl_CreateChannel(3), Tcl_RegisterChannel(3), Tcl_GetChannel(3), Tcl_GetStdChannel(3), Tcl_SetStdChannel(3), Tk_InitConsoleChannels(3), tclsh(1), wish(1), Tcl_Main(3), Tk_MainEx(3)
356
357	.SH KEYWORDS
358	standard channels