docs/manual/mod/mod_substitute.xml

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

<name>mod_substitute</name>
<description>Perform search and replace operations on response bodies</description>
<status>Extension</status>
<sourcefile>mod_substitute.c</sourcefile>
<identifier>substitute_module</identifier>
<compatibility>Available in Apache HTTP Server 2.2.7 and later</compatibility>

<summary>
    <p><module>mod_substitute</module> provides a mechanism to perform
    both regular expression and fixed string substitutions on
    response bodies.</p>
</summary>

<directivesynopsis>
<name>Substitute</name>
<description>Pattern to filter the response content</description>
<syntax>Substitute <var>s/pattern/substitution/[infq]</var></syntax>
<contextlist><context>directory</context>
<context>.htaccess</context></contextlist>
<override>FileInfo</override>

<usage>
    <p>The <directive>Substitute</directive> directive specifies a
    search and replace pattern to apply to the response body.</p>
    
    <p>The meaning of the pattern can be modified by using any
    combination of these flags:</p>
    
    <dl>
        <dt><code>i</code></dt>
        <dd>Perform a case-insensitive match.</dd>
        <dt><code>n</code></dt>
        <dd>By default the pattern is treated as a regular expression.
        Using the <code>n</code> flag forces the pattern to be treated
        as a fixed string.</dd>
        <dt><code>f</code></dt>
        <dd>The <code>f</code> flag causes mod_substitute to flatten the
        result of a substitution allowing for later substitutions to
        take place on the boundary of this one. This is the default.</dd>
        <dt><code>q</code></dt>
        <dd>The <code>q</code> flag causes mod_substitute to not
        flatten the buckets after each substitution. This can
        result in much faster response and a decrease in memory
        utilization, but should only be used if there is no possibility
        that the result of one substitution will ever match a pattern
        or regex of a subsequent one.</dd>
    </dl>
    
    <example><title>Example</title>
        &lt;Location /&gt;
        <indent>
            AddOutputFilterByType SUBSTITUTE text/html<br />
            Substitute s/foo/bar/ni<br />
        </indent>
        &lt;/Location&gt;
    </example>
    
    <p>If either the pattern or the substitution contain a slash
    character then an alternative delimiter should be used:</p>
    
    <example><title>Example of using an alternate delimiter</title>
        &lt;Location /&gt;
        <indent>
            AddOutputFilterByType SUBSTITUTE text/html<br />
            Substitute "s|&lt;BR */?&gt;|&lt;br /&gt;|i"
        </indent>
        &lt;/Location&gt;
    </example>

    <p>Backreferences can be used in the comparison and in the substitution,
    when regular expressions are used, as illustrated in the following example: </p>
    <example><title>Example of using backreferences and captures</title>
        &lt;Location /&gt;
        <indent>
            AddOutputFilterByType SUBSTITUTE text/html<br />
            # "foo=k,bar=k" -> "foo/bar=k" <br />
            Substitute "s|foo=(\w+),bar=\1|foo/bar=$1"
        </indent>
        &lt;/Location&gt;
    </example>

    <p>A common use scenario for <code>mod_substitute</code> is the
    situation in which a front-end server proxies requests to a back-end
    server which returns HTML with hard-coded embedded URLs that refer
    to the back-end server. These URLs don't work for the end-user,
    since the back-end server is unreachable.</p>

    <p>In this case, <code>mod_substutite</code> can be used to rewrite
    those URLs into something that will work from the front end:</p>

    <example><title>Rewriting URLs embedded in proxied content</title>
    ProxyPass /blog/ http://internal.blog.example.com<br />
    ProxyPassReverse /blog/ http://internal.blog.example.com/<br />
    <br />
    Substitute "s|http://internal.blog.example.com/|http://www.example.com/blog/|i"
    </example>

    <p><directive module="mod_proxy">ProxyPassReverse</directive>
    modifies any <code>Location</code> (redirect) headers that are sent
    by the back-end server, and, in this example,
    <code>Substitute</code> takes care of the rest of the problem by
    fixing up the HTML response as well.</p>

</usage>
</directivesynopsis>

</modulesynopsis>