Tcl Source Code

Check-in [af4a1c46e7]
Login
Bounty program for improvements to Tcl and certain Tcl packages.
Tcl 2019 Conference, Houston/TX, US, Nov 4-8
Send your abstracts to [email protected]
or submit via the online form by Sep 9.

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Improve the [chan] documentation
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk | msofer-wcodes-20050611
Files: files | file ages | folders
SHA1: af4a1c46e76a8ea23a3c3d811a365f7aea3e19c8
User & Date: dkf 2005-06-10 15:22:38
Context
2005-06-12
22:13
Simplify command compilation by moving numerous common stanzas into macros so that things say what t... check-in: 82d80d8b59 user: dkf tags: trunk
2005-06-10
15:22
Improve the [chan] documentation check-in: af4a1c46e7 user: dkf tags: trunk, msofer-wcodes-20050611
2005-06-09
16:24
fix to race condition in file mkdir and fix to glob documentation check-in: a6ebffa26e user: vincentdarley tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to ChangeLog.






1
2
3
4
5
6
7




2005-06-09  Vince Darley  <[email protected]>

	* generic/tclFCmd.c: fix to race condition in file mkdir [Bug 1217375]
	* doc/glob.n: improve glob documentation [Bug 1190891]

2005-06-09  Donal K. Fellows  <[email protected]>

>
>
>
>
>







1
2
3
4
5
6
7
8
9
10
11
12
2005-06-10  Donal K. Fellows  <[email protected]>

	* doc/chan.n: Fold in the descriptive parts of the documentation
	for all the commands that [chan] builds on top of.

2005-06-09  Vince Darley  <[email protected]>

	* generic/tclFCmd.c: fix to race condition in file mkdir [Bug 1217375]
	* doc/glob.n: improve glob documentation [Bug 1190891]

2005-06-09  Donal K. Fellows  <[email protected]>

Changes to doc/chan.n.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
..
15
16
17
18
19
20
21
22


23
24
25
26

27
28
29



30
31

32
33

































34
35

36
37
38
39
















40
































































































































































41
42


43
44
45















46
47
48
49














































50
51

52
53

54
55

56

57
58



59

60





















































61
62

63
64









65
66

67
68
69

70
71
72
73











74
75

76
77
78
79
80

81
82

83
84

































85
86
87
88

89
90
91
92
93
94
95
96


























97













98

99
100
101









102
























103
104
105


106




107
108

109
110
111

112
113
114
115
116
117
118
119
'\" 
'\" Copyright (c) 2005 Donal K. Fellows
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
'\" RCS: @(#) $Id: chan.n,v 1.1 2005/06/06 23:45:41 dkf Exp $
.so man.macros
.TH chan n 8.5 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
chan \- Read, write and manipulate channels
.SH SYNOPSIS
................................................................................
\fBchan \fIoption\fR ?\fIarg arg ...\fR?
.BE

.SH DESCRIPTION
.PP
This command provides several operations for reading from, writing to
and otherwise manipulating open channels (such as have been created
with the \fBopen\fR and \fBsocket\fR commands). \fIOption\fR indicates


what to do with the channel; any unique abbreviation for \fIoption\fR
is acceptable. Valid options are:
.TP
\fBchan blocked \fIchannelId\fR

Test whether the last input operation on the channel called
\fIchannelId\fR failed because it would have otherwise caused the
process to block.



.TP
\fBchan close \fIchannelId\fR

Close and destroy the channel called \fIchannelId\fR. Note that this
deletes all existing file-events registered on the channel.

































.TP
\fBchan configure \fIchannelId\fR ?\fIoptionName\fR? ?\fIvalue\fR? ?\fIoptionName value\fR?...

Query or set the configuration options of the channel named
\fIchannelId\fR (see \fBfconfigure\fR for details).
'\" FIXME: describe common channel options here and refer to creator
'\" commands for special option descriptions.
















.TP
































































































































































\fBchan copy \fIinput output\fR ?\fB\-size \fIsize\fR? ?\fB\-command \fIcallback\fR?
Copy the contents of the channel \fIinput\fR, which must have been


opened for reading, to the channel \fIoutput\fR, which must have been
opened for writing. If \fIsize\fR is specified, only that many bytes
will be transferred. If \fIcallback\fR is specified, this command















returns immediately and arranges for \fIcallback\fR to be called when
the requested transfer has completed or an error occurs (assuming that
the event loop is running) with extra arguments appended to
\fIcallback\fR to indicate what happened.














































.TP
\fBchan eof \fIchannelId\fR

Test whether the last input operation on the channel called
\fIchannelId\fR failed because the end of the data stream was reached.

.TP
\fBchan event \fIchannelId mode\fR ?\fIscript\fR?

Arrange for the Tcl script \fIscript\fR to be called whenever the

channel called \fIchannelId\fR enters the state described by
\fImode\fR (which must be either \fBreadable\fR or \fBwritable\fR). If



\fIscript\fR is omitted, the currently installed script is returned.

The callback is only performed if the event loop is being serviced.





















































.TP
\fBchan flush \fIchannelId\fR

Ensures that all pending output for the channel called \fIchannelId\fR
is written.









.TP
\fBchan gets \fIchannelId\fR ?\fIvarName\fR?

Reads a line from the channel called \fIchannelId\fR. If \fIvarName\fR
is not specified, the result of the command will be the line that has
been read (without a trailing newline character) or an empty string

upon error. If \fIvarName\fR is specified, the line that has been read
will be written to the variable called \fIvarName\fR and result will
be the number of characters that have been read or -1 if an error
occurred.











.TP
\fBchan names\fR ?\fIpattern\fR?

Produces a list of all channel names. If \fIpattern\fR is specified,
only those channel names that match it (according to the rules of
\fBstring match\fR) will be returned.
.TP
\fBchan puts\fR ?\fB\-nonewline\fR? ?\fIchannelId\fR? \fIstring\fR

Writes \fIstring\fR to the channel named \fIchannelId\fR (by default,
to the standard output stream) followed by a newline character. If the

optional flag \fB\-nonewline\fR is given, no trailing newline
character is written.

































.TP
\fBchan read \fIchannelId\fR ?\fInumChars\fR?
.TP
\fBchan read \fR?\fB\-nonewline\fR? \fIchannelId\fR

In the first form, the result will be the next \fInumChars\fR
characters read from the channel named \fIchannelId\fR; if
\fInumChars\fR is omitted, all characters up to the point when the
channel would signal a failure (whether an end-of-file, blocked or
other error condition) are read. In the second form (i.e. when
\fInumChars\fR has been omitted) the flag \fB\-nonewline\fR may be
given to indicate that any trailing newline in the string that has
been read should be trimmed.


























.TP













\fBchan seek \fIchannelId offset\fR ?\fIorigin\fR?

Sets the current position within the underlying data stream for the
channel named \fIchannelId\fR to be \fIoffset\fR bytes relative to
\fIorigin\fR. \fIOrigin\fR should be one of \fBstart\fR (the default









origin), \fBcurrent\fR or \fBend\fR.
























.TP
\fBchan tell \fIchannelId\fR
Reports the current byte offset within the underlying data stream for


the channel named \fIchannelId\fR.




.TP
\fBchan truncate \fIchannelId\fR ?\fIlength\fR?

Sets the byte length of the underlying data stream for the channel
named \fIchannelId\fR to be \fIlength\fR (or to the current byte
offset within the underlying data stream if \fIlength\fR is omitted).


.SH "SEE ALSO"
close(n), eof(n), fblocked(n), fconfigure(n), fcopy(n), file(n),
fileevent(n), flush(n), gets(n), open(n), puts(n), read(n), seek(n),
socket(n), tell(n)

.SH KEYWORDS
channel, input, output, events, offset





|







 







|
>
>
|
|


>
|

|
>
>
>


>


>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>


>

|
<
<
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>

>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
|
<
>
>
|
<
<
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
|
<
<
<
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>


>

|
>

|
>
|
>
|
|
>
>
>
|
>
|
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>


>


>
>
>
>
>
>
>
>
>


>
|
|
|
>
|
|
|
<
>
>
>
>
>
>
>
>
>
>
>


>





>
|
<
>
|
<
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>




>








>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>

>
>
>
>
>
>
>
>
>
>
>
>
>

>
|
|
<
>
>
>
>
>
>
>
>
>
|
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>


<
>
>
|
>
>
>
>


>


|
>








1
2
3
4
5
6
7
8
9
10
11
12
13
14
..
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78


79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256

257
258
259


260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275



276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417

418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438

439
440

441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530

531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566

567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
'\" 
'\" Copyright (c) 2005 Donal K. Fellows
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
'\" RCS: @(#) $Id: chan.n,v 1.2 2005/06/10 15:22:43 dkf Exp $
.so man.macros
.TH chan n 8.5 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
chan \- Read, write and manipulate channels
.SH SYNOPSIS
................................................................................
\fBchan \fIoption\fR ?\fIarg arg ...\fR?
.BE

.SH DESCRIPTION
.PP
This command provides several operations for reading from, writing to
and otherwise manipulating open channels (such as have been created
with the \fBopen\fR and \fBsocket\fR commands, or the default named
channels \fBstdin\fR, \fBstdout\fR or \fBstderr\fR which correspond to
the process's standard input, output and error streams respectively).
\fIOption\fR indicates what to do with the channel; any unique
abbreviation for \fIoption\fR is acceptable. Valid options are:
.TP
\fBchan blocked \fIchannelId\fR
.
This tests whether the last input operation on the channel called
\fIchannelId\fR failed because it would have otherwise caused the
process to block, and returns 1 if that was the case. It returns 0
otherwise. Note that this only ever returns 1 when the channel has
been configured to be non-blocking; all Tcl channels have blocking
turned on by default.
.TP
\fBchan close \fIchannelId\fR
.
Close and destroy the channel called \fIchannelId\fR. Note that this
deletes all existing file-events registered on the channel.
.RS
.PP
As part of closing the channel, all buffered output is flushed to the
channel's outpuot device, any buffered input is discarded, the
underlying operating system resource is closed and \fIchannelId\fR
becomes unavailable for future use.
.PP
If the channel is blocking, the command does not return until all
output is flushed.  If the channel is nonblocking and there is
unflushed output, the channel remains open and the command returns
immediately; output will be flushed in the background and the channel
will be closed when all the flushing is complete.
.PP
If \fIchannelId\fR is a blocking channel for a command pipeline then
\fBchan close\fR waits for the child processes to complete.
.PP
If the channel is shared between interpreters, then \fBchan close\fR
makes \fIchannelId\fR unavailable in the invoking interpreter but has
no other effect until all of the sharing interpreters have closed the
channel. When the last interpreter in which the channel is registered
invokes \fBchan close\fR (or \fBclose\fR), the cleanup actions
described above occur. See the \fBinterp\fR command for a description
of channel sharing.
.PP
Channels are automatically closed when an interpreter is destroyed and
when the process exits.  Channels are switched to blocking mode, to
ensure that all output is correctly flushed before the process exits.
.PP
The command returns an empty string, and may generate an error if
an error occurs while flushing output.  If a command in a command
pipeline created with \fBopen\fR returns an error, \fBchan close\fR
generates an error (similar to the \fBexec\fR command.)
.RE
.TP
\fBchan configure \fIchannelId\fR ?\fIoptionName\fR? ?\fIvalue\fR? ?\fIoptionName value\fR?...
.
Query or set the configuration options of the channel named
\fIchannelId\fR.


.RS
.PP
If no \fIoptionName\fR or \fIvalue\fR arguments are supplied, the
command returns a list containing alternating option names and values
for the channel.  If \fIoptionName\fR is supplied but no \fIvalue\fR
then the command returns the current value of the given option.  If
one or more pairs of \fIoptionName\fR and \fIvalue\fR are supplied,
the command sets each of the named options to the corresponding
\fIvalue\fR; in this case the return value is an empty string.
.PP
The options described below are supported for all channels. In
addition, each channel type may add options that only it supports. See
the manual entry for the command that creates each type of channels
for the options that that specific type of channel supports. For
example, see the manual entry for the \fBsocket\fR command for its
additional options.
.TP
\fB\-blocking\fR \fIboolean\fR
.
The \fB\-blocking\fR option determines whether I/O operations on the
channel can cause the process to block indefinitely.  The value of the
option must be a proper boolean value.  Channels are normally in
blocking mode; if a channel is placed into nonblocking mode it will
affect the operation of the \fBchan gets\fR, \fBchan read\fR, \fBchan
puts\fR, \fBchan flush\fR, and \fBchan close\fR commands; see the
documentation for those commands for details.  For nonblocking mode to
work correctly, the application must be using the Tcl event loop
(e.g. by calling \fBTcl_DoOneEvent\fR or invoking the \fBvwait\fR
command).
.TP
\fB\-buffering\fR \fInewValue\fR
.
If \fInewValue\fR is \fBfull\fR then the I/O system will buffer output
until its internal buffer is full or until the \fBchan flush\fR
command is invoked. If \fInewValue\fR is \fBline\fR, then the I/O
system will automatically flush output for the channel whenever a
newline character is output. If \fInewValue\fR is \fBnone\fR, the I/O
system will flush automatically after every output operation.  The
default is for \fB\-buffering\fR to be set to \fBfull\fR except for
channels that connect to terminal-like devices; for these channels the
initial setting is \fBline\fR.  Additionally, \fBstdin\fR and
\fBstdout\fR are initially set to \fBline\fR, and \fBstderr\fR is set
to \fBnone\fR.
.TP
\fB\-buffersize\fR \fInewSize\fR
.
\fINewvalue\fR must be an integer; its value is used to set the size
of buffers, in bytes, subsequently allocated for this channel to store
input or output. \fINewvalue\fR must be a number of no more than one
million, allowing buffers of up to one million bytes in size.
.TP
\fB\-encoding\fR \fIname\fR
.
This option is used to specify the encoding of the channel as one of
the named encodings returned by \fBencoding names\fR or the special
value \fBbinary\fR, so that the data can be converted to and from
Unicode for use in Tcl.  For instance, in order for Tcl to read
characters from a Japanese file in \fBshiftjis\fR and properly process
and display the contents, the encoding would be set to \fBshiftjis\fR.
Thereafter, when reading from the channel, the bytes in the Japanese
file would be converted to Unicode as they are read.  Writing is also
supported \- as Tcl strings are written to the channel they will
automatically be converted to the specified encoding on output.
.RS
.PP
If a file contains pure binary data (for instance, a JPEG image), the
encoding for the channel should be configured to be \fBbinary\fR.  Tcl
will then assign no interpretation to the data in the file and simply
read or write raw bytes.  The Tcl \fBbinary\fR command can be used to
manipulate this byte-oriented data.  It is usually better to set the
\fB\-translation\fR option to \fBbinary\fR when you want to transfer
binary data, as this turns off the other automatic interpretations of
the bytes in the stream as well.
.PP
The default encoding for newly opened channels is the same platform-
and locale-dependent system encoding used for interfacing with the
operating system, as returned by \fBencoding system\fR.
.RE
.TP
\fB\-eofchar\fR \fIchar\fR
.TP
\fB\-eofchar\fR \fB{\fIinChar outChar\fB}\fR
.
This option supports DOS file systems that use Control-z (\ex1a) as an
end of file marker.  If \fIchar\fR is not an empty string, then this
character signals end-of-file when it is encountered during input.
For output, the end-of-file character is output when the channel is
closed.  If \fIchar\fR is the empty string, then there is no special
end of file character marker.  For read-write channels, a two-element
list specifies the end of file marker for input and output,
respectively.  As a convenience, when setting the end-of-file
character for a read-write channel you can specify a single value that
will apply to both reading and writing.  When querying the end-of-file
character of a read-write channel, a two-element list will always be
returned.  The default value for \fB\-eofchar\fR is the empty string
in all cases except for files under Windows.  In that case the
\fB\-eofchar\fR is Control-z (\ex1a) for reading and the empty string
for writing.
.TP
\fB\-translation\fR \fImode\fR
.TP
\fB\-translation\fR \fB{\fIinMode outMode\fB}\fR 
.
In Tcl scripts the end of a line is always represented using a single
newline character (\en).  However, in actual files and devices the end
of a line may be represented differently on different platforms, or
even for different devices on the same platform.  For example, under
UNIX newlines are used in files, whereas carriage-return-linefeed
sequences are normally used in network connections.  On input (i.e.,
with \fBchan gets\fP and \fBchan read\fP) the Tcl I/O system
automatically translates the external end-of-line representation into
newline characters.  Upon output (i.e., with \fBchan puts\fP), the I/O
system translates newlines to the external end-of-line representation.
The default translation mode, \fBauto\fP, handles all the common cases
automatically, but the \fB\-translation\fR option provides explicit
control over the end of line translations.
.RS
.PP
The value associated with \fB\-translation\fR is a single item for
read-only and write-only channels.  The value is a two-element list for
read-write channels; the read translation mode is the first element of
the list, and the write translation mode is the second element.  As a
convenience, when setting the translation mode for a read-write channel
you can specify a single value that will apply to both reading and
writing.  When querying the translation mode of a read-write channel, a
two-element list will always be returned.  The following values are
currently supported:
.TP
\fBauto\fR
.
As the input translation mode, \fBauto\fR treats any of newline
(\fBlf\fP), carriage return (\fBcr\fP), or carriage return followed by
a newline (\fBcrlf\fP) as the end of line representation.  The end of
line representation can even change from line-to-line, and all cases
are translated to a newline.  As the output translation mode,
\fBauto\fR chooses a platform specific representation; for sockets on
all platforms Tcl chooses \fBcrlf\fR, for all Unix flavors, it chooses
\fBlf\fR, and for the various flavors of Windows it chooses
\fBcrlf\fR.  The default setting for \fB\-translation\fR is \fBauto\fR
for both input and output.
.TP
\fBbinary\fR 
.
No end-of-line translations are performed.  This is nearly identical
to \fBlf\fP mode, except that in addition \fBbinary\fP mode also sets
the end-of-file character to the empty string (which disables it) and
sets the encoding to \fBbinary\fR (which disables encoding filtering).
See the description of \fB\-eofchar\fR and \fB\-encoding\fR for more
information.
.TP
\fBcr\fR
.
The end of a line in the underlying file or device is represented by a
single carriage return character.  As the input translation mode,
\fBcr\fP mode converts carriage returns to newline characters.  As the
output translation mode, \fBcr\fP mode translates newline characters
to carriage returns.
.TP
\fBcrlf\fR
.
The end of a line in the underlying file or device is represented by a
carriage return character followed by a linefeed character.  As the
input translation mode, \fBcrlf\fP mode converts
carriage-return-linefeed sequences to newline characters.  As the
output translation mode, \fBcrlf\fP mode translates newline characters
to carriage-return-linefeed sequences.  This mode is typically used on
Windows platforms and for network connections.
.TP
\fBlf\fR
.
The end of a line in the underlying file or device is represented by a
single newline (linefeed) character.  In this mode no translations
occur during either input or output.  This mode is typically used on
UNIX platforms.
.RE
.RE
.TP
\fBchan copy \fIinputChan outputChan\fR ?\fB\-size \fIsize\fR? ?\fB\-command \fIcallback\fR?

.
Copy data from the channel \fIinputChan\fR, which must have been
opened for reading, to the channel \fIoutputChan\fR, which must have


been opened for writing. The \fBchan copy\fR command leverages the
buffering in the Tcl I/O system to avoid extra copies and to avoid
buffering too much data in main memory when copying large files to
slow destinations like network sockets.
.RS
.PP
The \fBchan copy\fP command transfers data from \fIinputChan\fR until
end of file or \fIsize\fP bytes have been transferred. If no
\fB\-size\fP argument is given, then the copy goes until end of file.
All the data read from \fIinputChan\fR is copied to \fIoutputChan\fR.
Without the \fB\-command\fP option, \fBchan copy\fP blocks until the
copy is complete and returns the number of bytes written to
\fIoutputChan\fR.
.PP
The \fB\-command\fP argument makes \fBchan copy\fP work in the
background.  In this case it returns immediately and the



\fIcallback\fP is invoked later when the copy completes.  The
\fIcallback\fP is called with one or two additional arguments that
indicates how many bytes were written to \fIoutputChan\fR.  If an
error occurred during the background copy, the second argument is the
error string associated with the error.  With a background copy, it is
not necessary to put \fIinputChan\fR or \fIoutputChan\fR into
non-blocking mode; the \fBchan copy\fP command takes care of that
automatically.  However, it is necessary to enter the event loop by
using the \fBvwait\fP command or by using Tk.
.PP
You are not allowed to do other I/O operations with \fIinputChan\fR or
\fIoutputChan\fR during a background \fBchan copy\fR.  If either
\fIinputChan\fR or \fIoutputChan\fR get closed while the copy is in
progress, the current copy is stopped and the command callback is
\fInot\fP made.  If \fIinputChan\fR is closed, then all data already
queued for \fIoutputChan\fR is written out.
.PP
Note that \fIinputChan\fR can become readable during a background
copy.  You should turn off any \fBchan event\fP or \fBfileevent\fR
handlers during a background copy so those handlers do not interfere
with the copy.  Any I/O attempted by a \fBchan event\fR or
\fBfileevent\fP handler will get a "channel busy" error.
.PP
\fBChan copy\fR translates end-of-line sequences in \fIinputChan\fR
and \fIoutputChan\fR according to the \fB\-translation\fR option for
these channels (see \fBchan configure\fR above).  The translations
mean that the number of bytes read from \fIinputChan\fR can be
different than the number of bytes written to \fIoutputChan\fR.  Only
the number of bytes written to \fIoutputChan\fR is reported, either as
the return value of a synchronous \fBchan copy\fP or as the argument
to the callback for an asynchronous \fBchan copy\fP.
.PP
\fBChan copy\fR obeys the encodings and character translations
configured for the channels. This means that the incoming characters
are converted internally first UTF-8 and then into the encoding of the
channel \fBchan copy\fR writes to (see \fBchan configure\fR above for
details on the \fB\-encoding\fR and \fB\-translation\fR options). No
conversion is done if both channels are set to encoding \fBbinary\fR
and have matching translations. If only the output channel is set to
encoding \fBbinary\fR the system will write the internal UTF-8
representation of the incoming characters. If only the input channel
is set to encoding \fBbinary\fR the system will assume that the
incoming bytes are valid UTF-8 characters and convert them according
to the output encoding. The behaviour of the system for bytes which
are not valid UTF-8 characters is undefined in this case.
.RE
.TP
\fBchan eof \fIchannelId\fR
.
Test whether the last input operation on the channel called
\fIchannelId\fR failed because the end of the data stream was reached,
returning 1 if end-fo-file was reached, and 0 otherwise.
.TP
\fBchan event \fIchannelId event\fR ?\fIscript\fR?
.
Arrange for the Tcl script \fIscript\fR to be installed as a \fIfile
event handler\fR to be called whenever the channel called
\fIchannelId\fR enters the state described by \fIevent\fR (which must
be either \fBreadable\fR or \fBwritable\fR); only one such handler may
be installed per event per channel at a time.  If \fIscript\fR is the
empty string, the current handler is deleted (this also happens if the
channel is closed or the interpreter deleted).  If \fIscript\fR is
omitted, the currently installed script is returned (or an empty
string if no such handler is installed).  The callback is only
performed if the event loop is being serviced (e.g. via \fBvwait\fR or
\fBupdate\fR).
.RS
.PP
A file event handler is a binding between a channel and a script, such
that the script is evaluated whenever the channel becomes readable or
writable.  File event handlers are most commonly used to allow data to
be received from another process on an event-driven basis, so that the
receiver can continue to interact with the user or with other channels
while waiting for the data to arrive.  If an application invokes
\fBchan gets\fR or \fBchan read\fR on a blocking channel when there is
no input data available, the process will block; until the input data
arrives, it will not be able to service other events, so it will
appear to the user to ``freeze up''.  With \fBchan event\fR, the
process can tell when data is present and only invoke \fBchan gets\fR
or \fBchan read\fR when they won't block.
.PP
A channel is considered to be readable if there is unread data
available on the underlying device.  A channel is also considered to
be readable if there is unread data in an input buffer, except in the
special case where the most recent attempt to read from the channel
was a \fBchan gets\fR call that could not find a complete line in the
input buffer.  This feature allows a file to be read a line at a time
in nonblocking mode using events.  A channel is also considered to be
readable if an end of file or error condition is present on the
underlying file or device.  It is important for \fIscript\fR to check
for these conditions and handle them appropriately; for example, if
there is no special check for end of file, an infinite loop may occur
where \fIscript\fR reads no data, returns, and is immediately invoked
again.
.PP
A channel is considered to be writable if at least one byte of data
can be written to the underlying file or device without blocking, or
if an error condition is present on the underlying file or device.
Note that client sockets opened in asynchronous mode become writable
when they become connected or if the connection fails.
.PP
Event-driven I/O works best for channels that have been placed into
nonblocking mode with the \fBchan configure\fR command.  In blocking
mode, a \fBchan puts\fR command may block if you give it more data
than the underlying file or device can accept, and a \fBchan gets\fR
or \fBchan read\fR command will block if you attempt to read more data
than is ready; no events will be processed while the commands block.
In nonblocking mode \fBchan puts\fR, \fBchan read\fR, and \fBchan
gets\fR never block.
.PP
The script for a file event is executed at global level (outside the
context of any Tcl procedure) in the interpreter in which the \fBchan
event\fR command was invoked.  If an error occurs while executing the
script then the command registered with \fBinterp bgerror\fR is used
to report the error.  In addition, the file event handler is deleted
if it ever returns an error; this is done in order to prevent infinite
loops due to buggy handlers.
.RE
.TP
\fBchan flush \fIchannelId\fR
.
Ensures that all pending output for the channel called \fIchannelId\fR
is written.
.RS
.PP
If the channel is in blocking mode the command does not return until
all the buffered output has been flushed to the channel. If the
channel is in nonblocking mode, the command may return before all
buffered output has been flushed; the remainder will be flushed in the
background as fast as the underlying file or device is able to absorb
it.
.RE
.TP
\fBchan gets \fIchannelId\fR ?\fIvarName\fR?
.
Reads the next line from the channel called \fIchannelId\fR. If
\fIvarName\fR is not specified, the result of the command will be the
line that has been read (without a trailing newline character) or an
empty string upon end-of-file or, in non-blocking mode, if the data
available is exhausted. If \fIvarName\fR is specified, the line that
has been read will be written to the variable called \fIvarName\fR and
result will be the number of characters that have been read or -1 if

end-of-file was reached or, in non-blocking mode, if the data
available is exhausted.
.RS
.PP
If an end-of-file occurs while part way through reading a line, the
partial line will be returned (or written into \fIvarName\fR). When
\fIvarName\fR is not specified, the end-of-file case can be
distinguished from an empty line using the \fBchan eof\fR command, and
the partial-line-but-nonblocking case can be distinguished with the
\fBchan blocked\fR command.
.RE
.TP
\fBchan names\fR ?\fIpattern\fR?
.
Produces a list of all channel names. If \fIpattern\fR is specified,
only those channel names that match it (according to the rules of
\fBstring match\fR) will be returned.
.TP
\fBchan puts\fR ?\fB\-nonewline\fR? ?\fIchannelId\fR? \fIstring\fR
.
Writes \fIstring\fR to the channel named \fIchannelId\fR followed by a

newline character. A trailing newline character is written unless the
optional flag \fB\-nonewline\fR is given. If \fIchannelId\fR is

omitted, the string is written to the standard output channel,
\fBstdout\fR.
.RS
.PP
Newline characters in the output are translated by \fBchan puts\fR to
platform-specific end-of-line sequences according to the currently
configured value of the \fB\-translation\fR option for the channel
(for example, on PCs newlines are normally replaced with
carriage-return-linefeed sequences; see \fBchan configure\fR above for
details).
.PP
Tcl buffers output internally, so characters written with \fBchan
puts\fR may not appear immediately on the output file or device; Tcl
will normally delay output until the buffer is full or the channel is
closed.  You can force output to appear immediately with the \fBchan
flush\fR command.
.PP
When the output buffer fills up, the \fBchan puts\fR command will
normally block until all the buffered data has been accepted for
output by the operating system.  If \fIchannelId\fR is in nonblocking
mode then the \fBchan puts\fR command will not block even if the
operating system cannot accept the data.  Instead, Tcl continues to
buffer the data and writes it in the background as fast as the
underlying file or device can accept it.  The application must use the
Tcl event loop for nonblocking output to work; otherwise Tcl never
finds out that the file or device is ready for more output data.  It
is possible for an arbitrarily large amount of data to be buffered for
a channel in nonblocking mode, which could consume a large amount of
memory.  To avoid wasting memory, nonblocking I/O should normally be
used in an event-driven fashion with the \fBchan event\fR command
(don't invoke \fBchan puts\fR unless you have recently been notified
via a file event that the channel is ready for more output data).
.RE
.TP
\fBchan read \fIchannelId\fR ?\fInumChars\fR?
.TP
\fBchan read \fR?\fB\-nonewline\fR? \fIchannelId\fR
.
In the first form, the result will be the next \fInumChars\fR
characters read from the channel named \fIchannelId\fR; if
\fInumChars\fR is omitted, all characters up to the point when the
channel would signal a failure (whether an end-of-file, blocked or
other error condition) are read. In the second form (i.e. when
\fInumChars\fR has been omitted) the flag \fB\-nonewline\fR may be
given to indicate that any trailing newline in the string that has
been read should be trimmed.
.RS
.PP
If \fIchannelId\fR is in nonblocking mode, \fBchan read\fR may not
read as many characters as requested: once all available input has
been read, the command will return the data that is available rather
than blocking for more input.  If the channel is configured to use a
multi-byte encoding, then there may actually be some bytes remaining
in the internal buffers that do not form a complete character.  These
bytes will not be returned until a complete character is available or
end-of-file is reached.  The \fB\-nonewline\fR switch is ignored if
the command returns before reaching the end of the file.
.PP
\fBChan read\fR translates end-of-line sequences in the input into
newline characters according to the \fB\-translation\fR option for the
channel (see \fBchan configure\fR above for a discussion on the ways
in which \fBchan configure\fR will alter input).
.PP
When reading from a serial port, most applications should configure
the serial port channel to be nonblocking, like this:
.CS
\fBchan configure \fIchannelId \fB\-blocking \fI0\fR.
.CE
Then \fBchan read\fR behaves much like described above.  Note that
most serial ports are comparatively slow; it is entirely possible to
get a \fBreadable\fR event for each character read from them. Care
must be taken when using \fBchan read\fR on blocking serial ports:
.TP
\fBchan read \fIchannelId numChars\fR 
.
In this form \fBchan read\fR blocks until \fInumChars\fR have been
received from the serial port.
.TP
\fBchan read \fIchannelId\fR 
.
In this form \fBchan read\fR blocks until the reception of the
end-of-file character, see \fBchan configure -eofchar\fR. If there no
end-of-file character has been configured for the channel, then
\fBchan read\fR will block forever.
.RE
.TP
\fBchan seek \fIchannelId offset\fR ?\fIorigin\fR?
.
Sets the current access position within the underlying data stream for
the channel named \fIchannelId\fR to be \fIoffset\fR bytes relative to

\fIorigin\fR. \fIOffset\fR must be an integer (which may be negative)
and \fIorigin\fR must be one of the following:
.RS
.TP 10
\fBstart\fR
.
The new access position will be \fIoffset\fR bytes from the start
of the underlying file or device.
.TP 10
\fBcurrent\fR
.
The new access position will be \fIoffset\fR bytes from the current
access position; a negative \fIoffset\fR moves the access position
backwards in the underlying file or device.
.TP 10
\fBend\fR
.
The new access position will be \fIoffset\fR bytes from the end of the
file or device.  A negative \fIoffset\fR places the access position
before the end of file, and a positive \fIoffset\fR places the access
position after the end of file.
.PP
The \fIorigin\fR argument defaults to \fBstart\fR.
.PP
\fBChan seek\fR flushes all buffered output for the channel before the
command returns, even if the channel is in nonblocking mode.  It also
discards any buffered and unread input.  This command returns an empty
string.  An error occurs if this command is applied to channels whose
underlying file or device does not support seeking.
.PP
Note that \fIoffset\fR values are byte offsets, not character offsets.
Both \fBchan seek\fR and \fBchan tell\fR operate in terms of bytes,
not characters, unlike \fBchan read\fR.
.RE
.TP
\fBchan tell \fIchannelId\fR

.
Returns a number giving the current access position within the
underlying data stream for the channel named \fIchannelId\fR. This
value returned is a byte offset that can be passed to \fBchan seek\fR
in order to set the channel to a particular position.  Note that this
value is in terms of bytes, not characters like \fBchan read\fR.  The
value returned is -1 for channels that do not support seeking.
.TP
\fBchan truncate \fIchannelId\fR ?\fIlength\fR?
.
Sets the byte length of the underlying data stream for the channel
named \fIchannelId\fR to be \fIlength\fR (or to the current byte
offset within the underlying data stream if \fIlength\fR is
omitted). The channel is flushed before truncation.

.SH "SEE ALSO"
close(n), eof(n), fblocked(n), fconfigure(n), fcopy(n), file(n),
fileevent(n), flush(n), gets(n), open(n), puts(n), read(n), seek(n),
socket(n), tell(n)

.SH KEYWORDS
channel, input, output, events, offset