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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>
<programlisting>
env = Environment()
lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
env.Precious(lib)
</programlisting>
<para>
Although the output doesn't look any different,
&SCons; does not, in fact,
delete the target library before rebuilding it:
</para>
<screen>
% <userinput>scons -Q</userinput>
cc -c -o f1.o f1.c
cc -c -o f2.o f2.c
cc -c -o f3.o f3.c
ar r libfoo.a f1.o f2.o f3.o
ranlib libfoo.a
</screen>
<para>
&SCons; will, however, still delete files marked as &Precious;
when the <literal>-c</literal> option is used.
</para>
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