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
|
<?xml version='1.0'?>
<!DOCTYPE sconsdoc [
<!ENTITY % scons SYSTEM "../scons.mod">
%scons;
<!ENTITY % builders-mod SYSTEM "../generated/builders.mod">
%builders-mod;
<!ENTITY % functions-mod SYSTEM "../generated/functions.mod">
%functions-mod;
<!ENTITY % tools-mod SYSTEM "../generated/tools.mod">
%tools-mod;
<!ENTITY % variables-mod SYSTEM "../generated/variables.mod">
%variables-mod;
]>
<chapter id="chap-factories"
xmlns="http://www.scons.org/dbxsd/v1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 scons.xsd">
<title>Platform-Independent File System Manipulation</title>
<!--
__COPYRIGHT__
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-->
<para>
&SCons; provides a number of platform-independent functions,
called <literal>factories</literal>,
that perform common file system manipulations
like copying, moving or deleting files and directories,
or making directories.
These functions are <literal>factories</literal>
because they don't perform the action
at the time they're called,
they each return an &Action; object
that can be executed at the appropriate time.
</para>
<section>
<title>Copying Files or Directories: The &Copy; Factory</title>
<para>
Suppose you want to arrange to make a copy of a file,
and don't have a suitable pre-existing builder.
<footnote>
<para>
Unfortunately, in the early days of SCons design,
we used the name &Copy; for the function that
returns a copy of the environment,
otherwise that would be the logical choice for
a Builder that copies a file or directory tree
to a target location.
</para>
</footnote>
One way would be to use the &Copy; action factory
in conjunction with the &Command; builder:
</para>
<scons_example name="factories_Copy1">
<file name="SConstruct" printme="1">
Command("file.out", "file.in", Copy("$TARGET", "$SOURCE"))
</file>
<file name="file.in">file.in</file>
</scons_example>
<para>
Notice that the action returned by the &Copy; factory
will expand the &cv-link-TARGET; and &cv-link-SOURCE; strings
at the time &file_out; is built,
and that the order of the arguments
is the same as that of a builder itself--that is,
target first, followed by source:
</para>
<scons_output example="factories_Copy1">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
You can, of course, name a file explicitly
instead of using &cv-TARGET; or &cv-SOURCE;:
</para>
<scons_example name="factories_Copy2">
<file name="SConstruct" printme="1">
Command("file.out", [], Copy("$TARGET", "file.in"))
</file>
<file name="file.in">file.in</file>
</scons_example>
<para>
Which executes as:
</para>
<scons_output example="factories_Copy2">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
The usefulness of the &Copy; factory
becomes more apparent when
you use it in a list of actions
passed to the &Command; builder.
For example, suppose you needed to run a
file through a utility that only modifies files in-place,
and can't "pipe" input to output.
One solution is to copy the source file
to a temporary file name,
run the utility,
and then copy the modified temporary file to the target,
which the &Copy; factory makes extremely easy:
</para>
<scons_example name="factories_Copy3">
<file name="S" printme="1">
Command("file.out", "file.in",
[
Copy("tempfile", "$SOURCE"),
"modify tempfile",
Copy("$TARGET", "tempfile"),
])
</file>
<file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
</file>
<file name="file.in">file.in</file>
<file name="modify" chmod="0755">
touch $*
</file>
</scons_example>
<para>
The output then looks like:
</para>
<scons_output example="factories_Copy3">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Deleting Files or Directories: The &Delete; Factory</title>
<para>
If you need to delete a file,
then the &Delete; factory
can be used in much the same way as
the &Copy; factory.
For example, if we want to make sure that
the temporary file
in our last example doesn't exist before
we copy to it,
we could add &Delete; to the beginning
of the command list:
</para>
<scons_example name="factories_Delete1">
<file name="S" printme="1">
Command("file.out", "file.in",
[
Delete("tempfile"),
Copy("tempfile", "$SOURCE"),
"modify tempfile",
Copy("$TARGET", "tempfile"),
])
</file>
<file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
</file>
<file name="file.in">file.in</file>
<file name="modify" chmod="0755">
touch $*
</file>
</scons_example>
<para>
Which then executes as follows:
</para>
<scons_output example="factories_Delete1">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
Of course, like all of these &Action; factories,
the &Delete; factory also expands
&cv-link-TARGET; and &cv-link-SOURCE; variables appropriately.
For example:
</para>
<scons_example name="factories_Delete2">
<file name="SConstruct" printme="1">
Command("file.out", "file.in",
[
Delete("$TARGET"),
Copy("$TARGET", "$SOURCE")
])
</file>
<file name="file.in">file.in</file>
</scons_example>
<para>
Executes as:
</para>
<scons_output example="factories_Delete2">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
<para>
Note, however, that you typically don't need to
call the &Delete; factory explicitly in this way;
by default, &SCons; deletes its target(s)
for you before executing any action.
</para>
<para>
One word of caution about using the &Delete; factory:
it has the same variable expansions available
as any other factory, including the &cv-SOURCE; variable.
Specifying <literal>Delete("$SOURCE")</literal>
is not something you usually want to do!
</para>
</section>
<section>
<title>Moving (Renaming) Files or Directories: The &Move; Factory</title>
<para>
The &Move; factory
allows you to rename a file or directory.
For example, if we don't want to copy the temporary file,
we could use:
</para>
<scons_example name="factories_Move">
<file name="S" printme="1">
Command("file.out", "file.in",
[
Copy("tempfile", "$SOURCE"),
"modify tempfile",
Move("$TARGET", "tempfile"),
])
</file>
<file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
</file>
<file name="file.in">file.in</file>
<file name="modify" chmod="0755">
touch $*
</file>
</scons_example>
<para>
Which would execute as:
</para>
<scons_output example="factories_Move">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Updating the Modification Time of a File: The &Touch; Factory</title>
<para>
If you just need to update the
recorded modification time for a file,
use the &Touch; factory:
</para>
<scons_example name="factories_Touch">
<file name="S" printme="1">
Command("file.out", "file.in",
[
Copy("$TARGET", "$SOURCE"),
Touch("$TARGET"),
])
</file>
<file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
</file>
<file name="file.in">file.in</file>
</scons_example>
<para>
Which executes as:
</para>
<scons_output example="factories_Touch">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Creating a Directory: The &Mkdir; Factory</title>
<para>
If you need to create a directory,
use the &Mkdir; factory.
For example, if we need to process
a file in a temporary directory
in which the processing tool
will create other files that we don't care about,
you could use:
</para>
<scons_example name="factories_Mkdir">
<file name="S" printme="1">
Command("file.out", "file.in",
[
Delete("tempdir"),
Mkdir("tempdir"),
Copy("tempdir/${SOURCE.file}", "$SOURCE"),
"process tempdir",
Move("$TARGET", "tempdir/output_file"),
Delete("tempdir"),
])
</file>
<file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
</file>
<file name="file.in">file.in</file>
<file name="process" chmod="0755">
touch $*
</file>
</scons_example>
<para>
Which executes as:
</para>
<scons_output example="factories_Mkdir">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Changing File or Directory Permissions: The &Chmod; Factory</title>
<para>
To change permissions on a file or directory,
use the &Chmod; factory.
The permission argument uses POSIX-style
permission bits and should typically
be expressed as an octal,
not decimal, number:
</para>
<scons_example name="factories_Chmod">
<file name="SConstruct" printme="1">
Command("file.out", "file.in",
[
Copy("$TARGET", "$SOURCE"),
Chmod("$TARGET", 0755),
])
</file>
<file name="file.in">file.in</file>
</scons_example>
<para>
Which executes:
</para>
<scons_output example="factories_Chmod">
<scons_output_command suffix="1">scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Executing an action immediately: the &Execute; Function</title>
<para>
We've been showing you how to use &Action; factories
in the &Command; function.
You can also execute an &Action; returned by a factory
(or actually, any &Action;)
at the time the &SConscript; file is read
by using the &Execute; function.
For example, if we need to make sure that
a directory exists before we build any targets,
</para>
<scons_example name="factories_Execute">
<file name="SConstruct" printme="1">
Execute(Mkdir('__ROOT__/tmp/my_temp_directory'))
</file>
</scons_example>
<para>
Notice that this will
create the directory while
the &SConscript; file is being read:
</para>
<scons_output example="factories_Execute">
<scons_output_command suffix="1">scons</scons_output_command>
</scons_output>
<para>
If you're familiar with Python,
you may wonder why you would want to use this
instead of just calling the native Python
<function>os.mkdir()</function> function.
The advantage here is that the &Mkdir;
action will behave appropriately if the user
specifies the &SCons; <option>-n</option> or
<option>-q</option> options--that is,
it will print the action but not actually
make the directory when <option>-n</option> is specified,
or make the directory but not print the action
when <option>-q</option> is specified.
</para>
<para>
The &Execute; function returns the exit status
or return value of the underlying action being executed.
It will also print an error message if the action
fails and returns a non-zero value.
&SCons; will <emphasis>not</emphasis>, however,
actually stop the build if the action fails.
If you want the build to stop
in response to a failure in an action called by &Execute;,
you must do so by explicitly
checking the return value
and calling the &Exit; function
(or a Python equivalent):
</para>
<sconstruct>
if Execute(Mkdir('__ROOT__/tmp/my_temp_directory')):
# A problem occurred while making the temp directory.
Exit(1)
</sconstruct>
</section>
</chapter>
|