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<para>
If you're completely new to a build system like &SCons;, this chapter is written for you.
We very briefly discuss the general setup of your project, regarding the &SCons; configuration
files &SConstruct; and &SConscript;.
Additionally, a few guidelines are provided about how to start a project...hopefully preventing you from
running into dead-end after dead-end later on.
</para>
<section>
<title>SCons files</title>
<para>
Okay, so you have a version of your shiny new project, ready for its very first &SCons; build. Or maybe you decided
to drop make/autotools, and want to try out &SCons; on the cool media-message-mailing library that you already provide
on Sourceforge (Tigris, Github, Bitbucket, Launchpad...).
</para>
<para>
Let's say you have a source folder in your file system, a directory with all the input files for the build process.
These may be C or C++ files, TeX/LaTeX sources or a Java package tree. For a start we also assume that you want the
resulting files, like libs, executables, JARs and PDFs, to be created in the same folder structure. Alongside your
sources, so to speak.
</para>
<para>
In order to get &SCons; going you have to give it your input files and tell it what to build. Like in most build systems,
this is done by writing a special text file (or several of them) further describing your build setup. You place this
file, named &SConstruct; (see <xref linkend="chap-simple"></xref>), at the top of your source folder tree:
</para>
<screen>
yoursrc
yourlib1
*.cpp/h
yourlib2
*.cpp/h
yourexe
*.cpp/h
README
INSTALL
SConstruct
</screen>
<para>
To start a build, you open a terminal (text console, prompt, shell,...whatever it is called in your current system) and
change into the folder with the &SConstruct; in it. Having &SCons; properly installed (see <xref linkend="chap-build-install"></xref>), you call the command
</para>
<screen>
% <userinput>scons</userinput>
</screen>
<para>
and the processing starts. &SCons; reads your &SConstruct; and starts to build things for you, hopefully.
</para>
<para>
So much for a very quick start and the basics about how to get &SCons; going.
A discussion of &SCons; at great length can be found in the following
chapters and sections. Read on please, to learn more about all the available features and possibilities...
</para>
</section>
<section>
<title>A few additional guidelines</title>
<para>
With &SCons; and the power of Python as backup, you are pretty much free to do anything
you like. However, when you start without any prior experience a few pointers might
help as a good foundation for your work. That's exactly what the following list is there
for. A few best practices and you can have your pick...or roll your own stuff.
</para>
<itemizedlist>
<listitem>
<para><emphasis>Think in modules</emphasis>: Try to create an &SConscript; for
each subfolder, containing one of your libs or executables.
Then, call these &SConscript;s from a single &SConstruct; at the top of your
build directory.
</para>
<para>
From what our experience tells us, this is the setup that offers you the most flexibility
regarding build options and variant dirs. It may look a bit complicated and overdone
right now, but starting this way pays off really fast.
</para>
<para>
A simple example:
</para>
<screen>
yoursrc
yourlib1
SConscript
*.cpp/h
yourlib2
SConscript
*.cpp/h
SConstruct
</screen>
<para>
would include the &SConscript;s by
</para>
<screen>
SConscript(['yourlib1/SConscript'])
SConscript(['yourlib2/SConscript'])
</screen>
<para>
in the &SConstruct;.
</para>
<para>Check out <xref linkend="sect-sconstruct-file"></xref> and <xref linkend="chap-hierarchical"></xref> for more infos about this.
</para>
</listitem>
<listitem>
<para><emphasis>Configure at the top and reuse</emphasis>: Configure the environments that you
need, in your &SConstruct; file at the very top of your build tree.
Don't create them anew in each &SConscript; (module) but export them globally
and use Clone() to make a local copy where required.
</para>
<para>
In your &SConstruct; at the top you can create and export a basic Environment as:
<screen>
env = Environment(tools=['default'], CC='/opt/arm-gcc_4.01/bin/gcc')
Export('env')
</screen>
and access it in one of your &SConscript;s by:
<screen>
Import('env')
debug_env = env.Clone()
debug_env.Append(CCFLAGS=['-g'])
debug_env.Program('foo','foo.c')
</screen>
</para>
<para>
Pointers to more info are <xref linkend="chap-environments"></xref>,
especially <xref linkend="sect-construction-environments"></xref> and
<xref linkend="sect-clone-environments"></xref>, as well as <xref linkend="sect-sharing-environments"></xref>.
</para>
</listitem>
<listitem>
<para><emphasis>Think in dependencies</emphasis>: &SCons; works by knowing dependencies. Internally,
it builds a large dependency
graph (DAG, <emphasis>directed acyclic graph</emphasis>) for all its build tasks. The single
files are managed as nodes, while the edges represent the build dependencies.
No dependency, no build. It's that simple.
Try to forget about those phony targets, that you may have used all throughout <literal>make</literal> (shudder).
Check out this User manual, or ask for help on the &SCons; mailing lists. Don't fall back to those
bad old habits and hack around, only because you're under time pressure. Try to do your builds the &SCons; way!
</para>
<para>
<xref linkend="chap-depends"></xref>, <xref linkend="sect-implicit-dependencies"></xref>,
<xref linkend="chap-builders-writing"></xref>, and <xref linkend="chap-scanners"></xref>
will tell you more about how dependencies work in &SCons; and can be bent
the way you want them.
</para>
</listitem>
<listitem>
<para><emphasis>Don't serialize</emphasis>: Finally, &SCons; is all about handling large projects with complicated builds. It is specially
optimized for working in parallel, and schedules all the single build tasks automatically.
This means that you can't easily get &SCons; to execute some scripts <literal>A</literal> and <literal>B</literal> in a predefined sequence (cf. <xref linkend="sect-order-independent"></xref>).
If you want to define a simple series of build tasks, that have to get executed in a fixed order regardless
of dependencies and timestamps, you should consider to use a simple shell or Python script as
wrapper instead.
Don't hurt your brain, while trying to force &SCons; into doing something that it wasn't designed for in the
first place.
</para>
<para>
&SCons; supports building multiple targets in parallel via a <literal>-j</literal> option that
takes, as its argument, the number of simultaneous tasks that may be
spawned: <quote><literal>scons -j 4</literal></quote> builds four targets
in parallel, for example.
</para>
</listitem>
</itemizedlist>
</section>
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