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<header>
<copyright>
<year>1997</year>
<year>2013</year>
<holder>Ericsson AB, All Rights Reserved</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
The Initial Developer of the Original Code is Ericsson AB.
</legalnotice>
<title>script</title>
<prepared>Martin Björklund</prepared>
<responsible>Bjarne Däcker</responsible>
<docno></docno>
<approved>Bjarne Däcker</approved>
<checked></checked>
<date>97-06-03</date>
<rev>A</rev>
<file>script.sgml</file>
</header>
<file>script</file>
<filesummary>Boot script</filesummary>
<description>
<p>The <em>boot script</em> 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 <c>erl -boot Name</c> starts the system with a boot
file called <c>Name.boot</c>, which is generated from the
<c>Name.script</c> file, using <c>systools:script2boot/1</c>.
</p>
<p>The <c>.script</c> file is generated by <c>systools</c> from a
<c>.rel</c> file and <c>.app</c> files.
</p>
</description>
<section>
<title>FILE SYNTAX</title>
<p>The boot script is stored in a file with the extension
<c>.script</c></p>
<p>The file has the following syntax:
</p>
<code type="none">
{script, {Name, Vsn},
[
{progress, loading},
{preLoaded, [Mod1, Mod2, ...]},
{path, [Dir1,"$ROOT/Dir",...]}.
{primLoad, [Mod1, Mod2, ...]},
...
{kernel_load_completed},
{progress, loaded},
{kernelProcess, Name, {Mod, Func, Args}},
...
{apply, {Mod, Func, Args}},
...
{progress, started}]}. </code>
<list type="bulleted">
<item><c>Name = string()</c> defines the name of the system.
</item>
<item><c>Vsn = string()</c> defines the version of the system.
</item>
<item><c>{progress, Term}</c> sets the "progress" of the
initialization program. The function <c>init:get_status()</c>
returns the current value of the progress, which is
<c>{InternalStatus,Term}</c>.
</item>
<item>
<p><c>{path, [Dir]}</c> where <c>Dir</c> is a string. This
argument sets the load path of the system to <c>[Dir]</c>. The
load path used to load modules is obtained from the initial
load path, which is given in the script file, together with
any path flags which were supplied in the command line
arguments. The command line arguments modify the path as
follows:</p>
<list type="bulleted">
<item><c>-pa Dir1 Dir2 ... DirN</c> adds the directories
<c>Dir1, Dir2, ..., DirN</c> to the front of the initial
load path.
</item>
<item><c>-pz Dir1 Dir2 ... DirN</c> adds the directories
<c>Dir1, Dir2, ..., DirN</c> to the end of the initial
load path.
</item>
<item>
<p><c>-path Dir1 Dir2 ... DirN</c> defines a set of
directories <c>Dir1, Dir2, ..., DirN</c> which replaces
the search path given in the script file. Directory names
in the path are interpreted as follows:</p>
<list type="bulleted">
<item>Directory names starting with <c>/</c> are assumed
to be absolute path names.
</item>
<item>Directory names not starting with <c>/</c> are
assumed to be relative the current working directory.
</item>
<item>The special <c>$ROOT</c> variable can only be used
in the script, not as a command line argument. The
given directory is relative the Erlang installation
directory.
</item>
</list>
</item>
</list>
</item>
<item><c>{primLoad, [Mod]}</c> loads the modules <c>[Mod]</c>
from the directories specified in <c>Path</c>. The script
interpreter fetches the appropriate module by calling the
function <c>erl_prim_loader:get_file(Mod)</c>. A fatal error
which terminates the system will occur if the module cannot be
located.
</item>
<item><c>{kernel_load_completed}</c> indicates that all modules
which <em>must</em> be loaded <em>before</em> any processes
are started are loaded. In interactive mode, all
<c>{primLoad,[Mod]}</c> commands interpreted after this
command are ignored, and these modules are loaded on demand.
In embedded mode, <c>kernel_load_completed</c> is ignored, and
all modules are loaded during system start.
</item>
<item><c>{kernelProcess, Name, {Mod, Func, Args}}</c> starts a
"kernel process". The kernel process <c>Name</c> is started
by evaluating <c>apply(Mod, Func, Args)</c> which is expected
to return <c>{ok, Pid}</c> or <c>ignore</c>. The <c>init</c>
process monitors the behaviour of <c>Pid</c> and terminates
the system if <c>Pid</c> dies. Kernel processes are key
components of the runtime system. Users do not normally add
new kernel processes.
</item>
<item><c>{apply, {Mod, Func, Args}}</c>. The init process simply
evaluates <c>apply(Mod, Func, Args)</c>. The system
terminates if this results in an error. The boot procedure
hangs if this function never returns.
</item>
</list>
<note>
<p>In the <c>interactive</c> system the code loader provides
demand driven code loading, but in the <c>embedded</c> system
the code loader loads all the code immediately. The same
version of <c>code</c> is used in both cases. The code server
calls <c>init:get_argument(mode)</c> to find out if it should
run in demand mode, or non-demand driven mode.
</p>
</note>
</section>
<section>
<title>SEE ALSO</title>
<p>systools(3)
</p>
</section>
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