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<!-- refpage --><center><h1>script</h1></center>
<h3>FILE</h3>
<div class="REFBODY">script</div>
<h3>FILE SUMMARY</h3>
<div class="REFBODY">Boot script</div>
<h3>DESCRIPTION</h3>
<div class="REFBODY"><p>
<p>The <strong>boot script</strong> describes how the Erlang runtime system is
started. It contains instructions on which code to load and
which processes and applications to start.
</p>
<p>The command <span class="code">erl -boot Name</span> starts the system with a boot
file called <span class="code">Name.boot</span>, which is generated from the
<span class="code">Name.script</span> file, using <span class="code">systools:script2boot/1</span>.
</p>
<p>The <span class="code">.script</span> file is generated by <span class="code">systools</span> from a
<span class="code">.rel</span> file and <span class="code">.app</span> files.
</p>
</p></div>
<h3><a name="id74387">FILE SYNTAX</a></h3>
<div class="REFBODY">
<p>The boot script is stored in a file with the extension
<span class="code">.script</span></p>
<p>The file has the following syntax:
</p>
<div class="example"><pre>
{script, {Name, Vsn},
[
{progress, loading},
{preLoaded, [Mod1, Mod2, ...]},
{path, [Dir1,"$ROOT/Dir",...]}.
{primLoad, [Mod1, Mod2, ...]},
...
{kernel_load_completed},
{progress, loaded},
{kernelProcess, Name, {Mod, Func, Args}},
...
{apply, {Mod, Func, Args}},
...
{progress, started}]}. </pre></div>
<ul>
<li>
<span class="code">Name = string()</span> defines the name of the system.
</li>
<li>
<span class="code">Vsn = string()</span> defines the version of the system.
</li>
<li>
<span class="code">{progress, Term}</span> sets the "progress" of the
initialization program. The function <span class="code">init:get_status()</span>
returns the current value of the progress, which is
<span class="code">{InternalStatus,Term}</span>.
</li>
<li>
<p><span class="code">{path, [Dir]}</span> where <span class="code">Dir</span> is a string. This
argument sets the load path of the system to <span class="code">[Dir]</span>. The
load path used to load modules is obtained from the initial
load path, which is given in the script file, together with
any path flags which were supplied in the command line
arguments. The command line arguments modify the path as
follows:</p>
<ul>
<li>
<span class="code">-pa Dir1 Dir2 ... DirN</span> adds the directories
<span class="code">Dir1, Dir2, ..., DirN</span> to the front of the initial
load path.
</li>
<li>
<span class="code">-pz Dir1 Dir2 ... DirN</span> adds the directories
<span class="code">Dir1, Dir2, ..., DirN</span> to the end of the initial
load path.
</li>
<li>
<p><span class="code">-path Dir1 Dir2 ... DirN</span> defines a set of
directories <span class="code">Dir1, Dir2, ..., DirN</span> which replaces
the search path given in the script file. Directory names
in the path are interpreted as follows:</p>
<ul>
<li>Directory names starting with <span class="code">/</span> are assumed
to be absolute path names.
</li>
<li>Directory names not starting with <span class="code">/</span> are
assumed to be relative the current working directory.
</li>
<li>The special <span class="code">$ROOT</span> variable can only be used
in the script, not as a command line argument. The
given directory is relative the Erlang installation
directory.
</li>
</ul>
</li>
</ul>
</li>
<li>
<span class="code">{primLoad, [Mod]}</span> loads the modules <span class="code">[Mod]</span>
from the directories specified in <span class="code">Path</span>. The script
interpreter fetches the appropriate module by calling the
function <span class="code">erl_prim_loader:get_file(Mod)</span>. A fatal error
which terminates the system will occur if the module cannot be
located.
</li>
<li>
<span class="code">{kernel_load_completed}</span> indicates that all modules
which <strong>must</strong> be loaded <strong>before</strong> any processes
are started are loaded. In interactive mode, all
<span class="code">{primLoad,[Mod]}</span> commands interpreted after this
command are ignored, and these modules are loaded on demand.
In embedded mode, <span class="code">kernel_load_completed</span> is ignored, and
all modules are loaded during system start.
</li>
<li>
<span class="code">{kernelProcess, Name, {Mod, Func, Args}}</span> starts a
"kernel process". The kernel process <span class="code">Name</span> is started
by evaluating <span class="code">apply(Mod, Func, Args)</span> which is expected
to return <span class="code">{ok, Pid}</span> or <span class="code">ignore</span>. The <span class="code">init</span>
process monitors the behaviour of <span class="code">Pid</span> and terminates
the system if <span class="code">Pid</span> dies. Kernel processes are key
components of the runtime system. Users do not normally add
new kernel processes.
</li>
<li>
<span class="code">{apply, {Mod, Func, Args}}</span>. The init process simply
evaluates <span class="code">apply(Mod, Func, Args)</span>. The system
terminates if this results in an error. The boot procedure
hangs if this function never returns.
</li>
</ul>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>In the <span class="code">interactive</span> system the code loader provides
demand driven code loading, but in the <span class="code">embedded</span> system
the code loader loads all the code immediately. The same
version of <span class="code">code</span> is used in both cases. The code server
calls <span class="code">init:get_argument(mode)</span> to find out if it should
run in demand mode, or non-demand driven mode.
</p>
</p></div>
</div>
</div>
<h3><a name="id74653">SEE ALSO</a></h3>
<div class="REFBODY">
<p>systools(3)
</p>
</div>
</div>
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<hr>
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