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<!--

  Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 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>

    <programlisting>
        env = Environment(RANLIBCOM='')
        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 -o f1.o -c f1.c
        cc -o f2.o -c f2.c
        cc -o f3.o -c f3.c
        ar rc libfoo.a f1.o f2.o f3.o
    </screen>

    <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>

    <programlisting>
        env = Environment(RANLIBCOM='')
        lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
        env.NoClean(lib)
    </programlisting>

    <para>

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

    </para>

    <screen>
        % <userinput>scons -Q</userinput>
        cc -o f1.o -c f1.c
        cc -o f2.o -c f2.c
        cc -o f3.o -c f3.c
        ar rc libfoo.a f1.o f2.o f3.o
        % <userinput>scons -c</userinput>
        scons: Reading SConscript files ...
        scons: done reading SConscript files.
        scons: Cleaning targets ...
        Removed f1.o
        Removed f2.o
        Removed f3.o
        scons: done cleaning targets.
    </screen>

  </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>

    <programlisting>
        t = Command('foo.out', 'foo.in', 'build -o $TARGET $SOURCE')
        Clean(t, 'foo.log')
    </programlisting>

    <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>

    <screen>
        % <userinput>scons -Q</userinput>
        build -o foo.out foo.in
        % <userinput>scons -Q -c</userinput>
        Removed foo.out
        Removed foo.log
    </screen>

  </section>