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<!--
=head2 The C<AfterBuild> method
The C<AfterBuild> method evaluates the specified perl string after
building the given file or files (or finding that they are up to date).
The eval will happen once per specified file. C<AfterBuild> is called
as follows:
AfterBuild $env 'foo.o', qq(print "foo.o is up to date!\n");
The perl string is evaluated in the C<script> package, and has access
to all variables and subroutines defined in the F<Conscript> file in
which the C<AfterBuild> method is called.
-->
<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="ex1">
<file name="SConstruct" printme="1">
env = Environment()
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="ex1">
<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>
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