summaryrefslogtreecommitdiff
path: root/doc/user/file-removal.xml
blob: e772eebd9d4f7c009a31e64707dcacd4b3e94748 (plain)
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
<?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-file-removal"
         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 http://www.scons.org/dbxsd/v1.0/scons.xsd">
<title>Controlling Removal of Targets</title>

<!--

  Copyright (c) 2001 - 2019 The SCons Foundation

  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>

  There are two occasions when &SCons; will,
  by default, remove target files.
  The first is when &SCons; determines that
  an target file needs to be rebuilt
  and removes the existing version of the target
  before executing
  The second is when &SCons; is invoked with the
  <literal>-c</literal> option to "clean"
  a tree of its built targets.

  These behaviours can be suppressed with the
  &Precious; and &NoClean; functions, respectively.

  </para>

  <section>
  <title>Preventing target removal during build: the &Precious; Function</title>

    <para>

    By default, &SCons; removes targets before building them.
    Sometimes, however, this is not what you want.
    For example, you may want to update a library incrementally,
    not by having it deleted and then rebuilt from all
    of the constituent object files.
    In such cases, you can use the
    &Precious; method to prevent
    &SCons; from removing the target before it is built:

    </para>

    <scons_example name="fileremoval_precious-ex1">
      <file name="SConstruct" printme="1">
  env = Environment(RANLIBCOM='')
  lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
  env.Precious(lib)
      </file>
      <file name="f1.c">
int f1() { }
      </file>
      <file name="f2.c">
int f2() { }
      </file>
      <file name="f3.c">
int f3() { }
      </file>
    </scons_example>

    <para>

    Although the output doesn't look any different,
    &SCons; does not, in fact,
    delete the target library before rebuilding it:

    </para>

    <scons_output example="fileremoval_precious-ex1" suffix="1">
        <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

    &SCons; will, however, still delete files marked as &Precious;
    when the <literal>-c</literal> option is used.

    </para>

  </section>

  <section>
  <title>Preventing target removal during clean: the &NoClean; Function</title>

    <para>

    By default, &SCons; removes all built targets when invoked
    with the <literal>-c</literal> option to clean a source tree
    of built targets.
    Sometimes, however, this is not what you want.
    For example, you may want to remove only intermediate generated files
    (such as object files),
    but leave the final targets
    (the libraries)
    untouched.

    In such cases, you can use the &NoClean; method to prevent &SCons;
    from removing a target during a clean:

    </para>

    <scons_example name="fileremoval_noclean-ex1">
      <file name="SConstruct" printme="1">
env = Environment(RANLIBCOM='')
lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
env.NoClean(lib)
      </file>
      <file name="f1.c">
int f1() { }
      </file>
      <file name="f2.c">
int f2() { }
      </file>
      <file name="f3.c">
int f3() { }
      </file>
    </scons_example>

    <para>

    Notice that the <filename>libfoo.a</filename>
    is not listed as a removed file:

    </para>

    <scons_output example="fileremoval_noclean-ex1" suffix="1">
        <scons_output_command>scons -Q</scons_output_command>
        <scons_output_command>scons -c</scons_output_command>
    </scons_output>

  </section>

  <section>
  <title>Removing additional files during clean: the &Clean; Function</title>

    <para>

    There may be additional files that you want removed
    when the <literal>-c</literal> option is used,
    but which &SCons; doesn't know about
    because they're not normal target files.
    For example, perhaps a command you invoke
    creates a log file as
    part of building the target file you want.
    You would like the log file cleaned,
    but you don't want to have to teach
    SCons that the command
    "builds" two files.

    </para>

    <para>

    You can use the &Clean; function to arrange for additional files
    to be removed when the <literal>-c</literal> option is used.
    Notice, however, that the &Clean; function takes two arguments,
    and the <emphasis>second</emphasis> argument
    is the name of the additional file you want cleaned
    (<filename>foo.log</filename> in this example):

    </para>

    <scons_example name="fileremoval_clean-ex1">
      <file name="S" printme="1">
t = Command('foo.out', 'foo.in', 'build -o $TARGET $SOURCE')
Clean(t, 'foo.log')
      </file>
      <file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
      </file>
      <file name="foo.in">
foo.in
      </file>
      <file name="foo.log">
foo.log
      </file>
      <file name="build" chmod="0o755">
cat $3 > $2
      </file>
    </scons_example>

    <para>

    The first argument is the target with which you want
    the cleaning of this additional file associated.
    In the above example,
    we've used the return value from the
    &Command; function,
    which represents the
    <filename>foo.out</filename>
    target.
    Now whenever the
    <filename>foo.out</filename> target is cleaned
    by the <literal>-c</literal> option,
    the <filename>foo.log</filename> file
    will be removed as well:

    </para>

    <scons_output example="fileremoval_clean-ex1" suffix="1">
        <scons_output_command>scons -Q</scons_output_command>
        <scons_output_command>scons -Q -c</scons_output_command>
    </scons_output>

  </section>

</chapter>