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<div id="preamble"><h1>Apache Module mod_substitute</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_substitute.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../fr/mod/mod_substitute.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a></p>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Perform search and replace operations on response bodies</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>substitute_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_substitute.c</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache HTTP Server 2.2.7 and later</td></tr></table>
<h3>Summary</h3>

    <p><code class="module"><a href="../mod/mod_substitute.html">mod_substitute</a></code> provides a mechanism to perform
    both regular expression and fixed string substitutions on
    response bodies.</p>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#substitute">Substitute</a></li>
</ul>
<ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>

<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="Substitute" id="Substitute">Substitute</a> <a name="substitute" id="substitute">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Pattern to filter the response content</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>Substitute <var>s/pattern/substitution/[infq]</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_substitute</td></tr>
</table>
    <p>The <code class="directive">Substitute</code> 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>

    <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">
&lt;Location /&gt;
    AddOutputFilterByType SUBSTITUTE text/html
    Substitute s/foo/bar/ni
&lt;/Location&gt;
        </pre>
</div>

    <p>If either the pattern or the substitution contain a slash
    character then an alternative delimiter should be used:</p>

    <div class="example"><h3>Example of using an alternate delimiter</h3><pre class="prettyprint lang-config">
&lt;Location /&gt;
    AddOutputFilterByType SUBSTITUTE text/html
    Substitute "s|&lt;BR */?&gt;|&lt;br /&gt;|i"
&lt;/Location&gt;
        </pre>
</div>

    <p>Backreferences can be used in the comparison and in the substitution,
    when regular expressions are used, as illustrated in the following example: </p>
    <div class="example"><h3>Example of using backreferences and captures</h3><pre class="prettyprint lang-config">
&lt;Location /&gt;
    AddOutputFilterByType SUBSTITUTE text/html
    # "foo=k,bar=k" -&gt; "foo/bar=k" 
    Substitute "s|foo=(\w+),bar=\1|foo/bar=$1"
&lt;/Location&gt;
    </pre>
</div>

    <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>

    <div class="example"><h3>Rewriting URLs embedded in proxied content</h3><pre class="prettyprint lang-config">
ProxyPass /blog/ http://internal.blog.example.com
ProxyPassReverse /blog/ http://internal.blog.example.com/

Substitute "s|http://internal.blog.example.com/|http://www.example.com/blog/|i"
    </pre>
</div>

    <p><code class="directive"><a href="../mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a></code>
    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>


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