apache/docs/manual/mod/mod_macro.xml

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<modulesynopsis metafile="mod_macro.xml.meta">

<name>mod_macro</name>
<description>Provides macros within apache httpd runtime configuration files</description>
<status>Base</status>
<sourcefile>mod_macro.c</sourcefile>
<identifier>macro_module</identifier>

<summary>

    <p>Provides macros within Apache httpd runtime configuration files,
    to ease the process of creating numerous similar configuration
    blocks. When the server starts up, the macros are expanded using the
    provided parameters, and the result is processed as along with the
    rest of the configuration file.</p>

</summary>

<section id="usage"><title>Usage</title>

<p>Macros are defined using <directive
type="section">Macro</directive> blocks, which contain the portion of
your configuration that needs to be repeated, complete with variables
for those parts that will need to be substituted.</p>

<p>For example,  you might use a macro to define a <directive
type="section">VirtualHost</directive> block, in order to define
multiple similar virtual hosts:</p>

<highlight language="config">
&lt;Macro VHost $name $domain&gt;
&lt;VirtualHost *:80&gt;
    ServerName $domain
    ServerAlias www.$domain

    DocumentRoot /var/www/vhosts/$name
    ErrorLog /var/log/httpd/$name.error_log
    CustomLog /var/log/httpd/$name.access_log combined
&lt;/VirtualHost&gt;
&lt;/Macro&gt;
</highlight>

<p>Macro names are case-insensitive, like httpd configuration
directives. However, variable names are case sensitive.</p>

<p>You would then invoke this macro several times to create virtual
hosts:</p>

<highlight language="config">
Use VHost example example.com
Use VHost myhost hostname.org
Use VHost apache apache.org

UndefMacro VHost
</highlight>

<p>At server startup time, each of these <directive>Use</directive>
invocations would be expanded into a full virtualhost, as
described by the <directive>Macro</directive> definition.</p>

<p>The <directive>UndefMacro</directive> directive is used so that later
macros using the same variable names don't result in conflicting
definitions.</p>

<p>A more elaborate version of this example may be seen below in the
Examples section.</p>

</section>

<section id="tips"><title>Tips</title>

<p>Parameter names should begin with a sigil such as <code>$</code>,
<code>%</code>, or <code>@</code>, so that they are clearly
identifiable, and also in order to help deal with interactions with
other directives, such as the core <directive
module="core">Define</directive> directive. Failure to do so will 
result in a warning. Nevertheless, you are encouraged to have a good
knowledge of your entire server configuration in order to avoid reusing
the same variables in different scopes, which can cause confusion.</p>

<p>Parameters prefixed with either <code>$</code> or <code>%</code> are
not escaped. Parameters prefixes with <code>@</code> are escaped in
quotes.</p>

<p>Avoid using a parameter which contains another parameter as a prefix,
(For example, <code>$win</code> and <code>$winter</code>) as this may
cause confusion at expression evaluation time. In the event of such
confusion, the longest possible parameter name is used.</p>

<p>If you want to use a value within another string, it is useful to
surround the parameter in braces, to avoid confusion:</p>

<highlight language="config">
&lt;Macro DocRoot ${docroot}&gt;
    DocumentRoot /var/www/${docroot}/htdocs
&lt;/Macro&gt;
</highlight>

</section>

<section id="examples">
<title>Examples</title>

<section>
<title>Virtual Host Definition</title>

<p>A common usage of <module>mod_macro</module> is for the creation of
dynamically-generated virtual hosts.</p>

<highlight language="config">
## Define a VHost Macro for repetitive configurations

&lt;Macro VHost $host $port $dir&gt;
  Listen $port
  &lt;VirtualHost *:$port&gt;

    ServerName $host
    DocumentRoot $dir

    # Public document root
    &lt;Directory $dir&gt;
        Require all granted
    &lt;/Directory&gt;

    # limit access to intranet subdir.
    &lt;Directory $dir/intranet&gt;
      Require ip 10.0.0.0/8
    &lt;/Directory&gt;
  &lt;/VirtualHost&gt;
&lt;/Macro&gt;

## Use of VHost with different arguments.

Use VHost www.apache.org 80 /vhosts/apache/htdocs
Use VHost example.org 8080 /vhosts/example/htdocs
Use VHost www.example.fr 1234 /vhosts/example.fr/htdocs
</highlight>
</section> <!-- Vhosts -->

<section>
<title>Removal of a macro definition</title>

<p>It's recommended that you undefine a macro once you've used it. This
avoids confusion in a complex configuration file where there may be
conflicts in variable names.</p>

<highlight language="config">
&lt;Macro DirGroup $dir $group&gt;
  &lt;Directory $dir&gt;
    Require group $group
  &lt;/Directory&gt;
&lt;/Macro&gt;

Use DirGroup /www/apache/private private
Use DirGroup /www/apache/server  admin

UndefMacro DirGroup
</highlight>

</section> <!-- UndefMacro -->

</section> <!-- Example -->

<!-- Macro -->
<directivesynopsis type="section">
<name>Macro</name>
<description>Define a configuration file macro</description>
<syntax>
&lt;Macro <var>name</var> [<var>par1</var> .. <var>parN</var>]&gt;
... &lt;/Macro&gt;</syntax>
<contextlist>
<context>server config</context>
<context>virtual host</context>
<context>directory</context>
</contextlist>

<usage>
    <p>The <directive>Macro</directive> directive controls the definition of
    a macro within the server runtime configuration files.
    The first argument is the name of the macro.
    Other arguments are parameters to the macro. It is good practice to prefix
    parameter names with any of '<code>$%@</code>', and not macro names
    with such characters.
    </p>

    <highlight language="config">
&lt;Macro LocalAccessPolicy&gt;
    Require ip 10.2.16.0/24
&lt;/Macro&gt;

&lt;Macro RestrictedAccessPolicy $ipnumbers&gt;
    Require ip $ipnumbers
&lt;/Macro&gt;
    </highlight>
</usage>
</directivesynopsis>

<!-- Use -->
<directivesynopsis>
<name>Use</name>
<description>Use a macro</description>
<syntax>Use <var>name</var> [<var>value1</var> ... <var>valueN</var>]
</syntax>
<contextlist>
<context>server config</context>
<context>virtual host</context>
<context>directory</context>
</contextlist>

<usage>
    <p>The <directive>Use</directive> directive controls the use of a macro.
    The specified macro is expanded. It must be given the same number of
    arguments as in the  macro definition. The provided values are
    associated to their corresponding initial parameters and are substituted
    before processing.</p>

    <highlight language="config">
Use LocalAccessPolicy
...
Use RestrictedAccessPolicy "192.54.172.0/24 192.54.148.0/24"
    </highlight>

    <p>is equivalent, with the macros defined above, to:</p>

    <highlight language="config">
Require ip 10.2.16.0/24
...
Require ip 192.54.172.0/24 192.54.148.0/24
    </highlight>
</usage>

</directivesynopsis>

<!-- UndefMacro -->
<directivesynopsis>
<name>UndefMacro</name>
<description>Undefine a macro</description>

<syntax>UndefMacro <var>name</var></syntax>
<contextlist>
<context>server config</context>
<context>virtual host</context>
<context>directory</context>
</contextlist>

<usage>
    <p>The <directive>UndefMacro</directive> directive undefines a macro
    which has been defined before hand.</p>

    <highlight language="config">
UndefMacro LocalAccessPolicy
UndefMacro RestrictedAccessPolicy
    </highlight>
</usage>
</directivesynopsis>

</modulesynopsis>