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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"> en </a> |
<a href="../fr/mod/mod_substitute.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p>
</div>
<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></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>
<li><img alt="" src="../images/down.gif" /> <a href="#substituteinheritbefore">SubstituteInheritBefore</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#substitutemaxlinelength">SubstituteMaxLineLength</a></li>
</ul>
<h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_substitute">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_substitute">Report a bug</a></li></ul><h3>See also</h3>
<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><a title="Permanent link" href="#substitute" class="permalink">¶</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>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>"expr=" substitution values were added in 2.5.1</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 <code>mod_substitute</code> 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 <code>mod_substitute</code> 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>
<p>The <var>substitution</var> may contain literal text and regular
expression backreferences. If the substitution begins with the text
<code>expr=</code> it is intepreted as an <a href="../expr.html">
expression</a> which allows access to environment variables and
header values. </p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config"><Location "/">
AddOutputFilterByType SUBSTITUTE text/html
Substitute "s/foo/bar/ni"
</Location></pre>
</div>
<p>The character which is used to separate (or "delimit") the
various parts of the substituion string is referred to as the
"delimiter", and it is most common to use a slash for this
purpose.</p>
<p>If either the pattern or the substitution contain a slash
character then an alternative delimiter may be used to make the
directive more readable:</p>
<div class="example"><h3>Example of using an alternate delimiter</h3><pre class="prettyprint lang-config"><Location "/">
AddOutputFilterByType SUBSTITUTE text/html
Substitute "s|<BR */?>|<br />|i"
</Location></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"><Location "/">
AddOutputFilterByType SUBSTITUTE text/html
# "foo=k,bar=k" -> "foo/bar=k"
Substitute "s|foo=(\w+),bar=\1|foo/bar=$1|"
</Location></pre>
</div>
<p> When using an <a href="../expr.html">expression</a> for the
<var>substitution</var>, regular expression backreferences must be
backslash ('\') escaped as illustrated in the example below:</p>
<div class="example"><h3>Expression Example</h3><pre class="prettyprint lang-config"><Location "/">
AddOutputFilterByType SUBSTITUTE text/html
Substitute "s/example.com/expr=%{HTTP:HOST}/i"
Substitute "s/Hello, (\S+)/expr=Hello from %{REQUEST_URI}, \$1/i"
</Location></pre>
</div>
<div class="warning"><h3>Expressions and caching</h3>
<p>Caution must be exercised when performing substitutions that reference
HTTP request headers. Because this module operates after response headers
have been sent, the <a href="../expr.html">expression parser</a> cannot add
referenced HTTP request headers to the outgoing Vary header. </p>
</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_substitute</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 class="directive">Substitute</code> takes care of the rest of the problem by
fixing up the HTML response as well.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SubstituteInheritBefore" id="SubstituteInheritBefore">SubstituteInheritBefore</a> <a name="substituteinheritbefore" id="substituteinheritbefore">Directive</a><a title="Permanent link" href="#substituteinheritbefore" class="permalink">¶</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Change the merge order of inherited patterns</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SubstituteInheritBefore on|off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SubstituteInheritBefore on</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>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in httpd 2.4.17 and later</td></tr>
</table>
<p>Whether to apply the inherited <code class="directive"><a href="#substitute">Substitute</a></code>
patterns first (<code>on</code>), or after the ones of the current
context (<code>off</code>).
The latter was the default in versions 2.4 and earlier, but changed
starting with 2.5, hence <code class="directive">SubstituteInheritBefore</code>
set to <code>off</code> allows to restore the legacy behaviour.
<code class="directive">SubstituteInheritBefore</code> is itself inherited,
hence contexts that inherit it (those that don't specify their own
<code class="directive">SubstituteInheritBefore</code> value) will apply the
closest defined merge order.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SubstituteMaxLineLength" id="SubstituteMaxLineLength">SubstituteMaxLineLength</a> <a name="substitutemaxlinelength" id="substitutemaxlinelength">Directive</a><a title="Permanent link" href="#substitutemaxlinelength" class="permalink">¶</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum line size</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SubstituteMaxLineLength <var>bytes</var>(b|B|k|K|m|M|g|G)</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SubstituteMaxLineLength 1m</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>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in httpd 2.4.11 and later</td></tr>
</table>
<p>The maximum line size handled by <code class="module"><a href="../mod/mod_substitute.html">mod_substitute</a></code>
is limited to restrict memory use. The limit can be configured
using <code class="directive">SubstituteMaxLineLength</code>.
The value can be given as the number of bytes and can be suffixed
with a single letter <code>b</code>, <code>B</code>, <code>k</code>,
<code>K</code>, <code>m</code>, <code>M</code>, <code>g</code>,
<code>G</code> to provide the size in bytes, kilobytes, megabytes
or gigabytes respectively.</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config"><Location "/">
AddOutputFilterByType SUBSTITUTE text/html
SubstituteMaxLineLength 10m
Substitute "s/foo/bar/ni"
</Location></pre>
</div>
</div>
</div>
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