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  <section id="vcl-syntax">
<h1>VCL Syntax<a class="headerlink" href="#vcl-syntax" title="Link to this heading">¶</a></h1>
<p>VCL has inherited a lot from C and it reads much like simple C or Perl.</p>
<p>Blocks are delimited by curly brackets, statements end with semicolons,
and comments may be written as in C, C++ or Perl according to your own
preferences.</p>
<p>Note that VCL doesn’t contain any loops or jump statements.</p>
<p>This section provides an outline of the more important parts of the
syntax. For a full documentation of VCL syntax please see
<a class="reference internal" href="../reference/vcl.html#vcl-7"><span class="std std-ref">VCL</span></a> in the reference.</p>
<section id="strings">
<h2>Strings<a class="headerlink" href="#strings" title="Link to this heading">¶</a></h2>
<p>Basic strings are enclosed in “ … “, and may not contain newlines.</p>
<p>Backslash is not special, so for instance in <cite>regsub()</cite> you do not need
to do the “count-the-backslashes” polka:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">regsub</span><span class="p">(</span><span class="s2">&quot;barf&quot;</span><span class="p">,</span> <span class="s2">&quot;(b)(a)(r)(f)&quot;</span><span class="p">,</span> <span class="s2">&quot;</span><span class="se">\4\3\2</span><span class="s2">p&quot;</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="s2">&quot;frap&quot;</span>
</pre></div>
</div>
<p>Long strings are enclosed in {” … “} or “”” … “””. They may contain
any character including “, newline and other control characters except
for the NUL (0x00) character. If you really want NUL characters in a
string there is a VMOD that makes it possible to create such strings.</p>
</section>
<section id="access-control-lists-acls">
<span id="vcl-syntax-acl"></span><h2>Access control lists (ACLs)<a class="headerlink" href="#access-control-lists-acls" title="Link to this heading">¶</a></h2>
<p>An ACL declaration creates and initializes a named access control list
which can later be used to match client addresses:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>acl local {
  &quot;localhost&quot;;         // myself
  &quot;192.0.2.0&quot;/24;      // and everyone on the local network
  ! &quot;192.0.2.23&quot;;      // except for the dialin router
}
</pre></div>
</div>
<p>If an ACL entry specifies a host name which Varnish is unable to
resolve, it will match any address it is compared to. Consequently,
if it is preceded by a negation mark, it will reject any address it is
compared to, which may not be what you intended. If the entry is
enclosed in parentheses, however, it will simply be ignored.</p>
<p>To match an IP address against an ACL, simply use the match operator:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="p">(</span><span class="n">client</span><span class="o">.</span><span class="n">ip</span> <span class="o">~</span> <span class="n">local</span><span class="p">)</span> <span class="p">{</span>
  <span class="k">return</span> <span class="p">(</span><span class="n">pipe</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<p>In Varnish versions before 7.0, ACLs would always emit a <cite>VCL_acl</cite>
record in the VSL log, from 7.0 and forward, this must be explicitly
enabled by specifying the <cite>+log</cite> flag:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>acl local +log {
  &quot;localhost&quot;;         // myself
  &quot;192.0.2.0&quot;/24;      // and everyone on the local network
  ! &quot;192.0.2.23&quot;;      // except for the dialin router
}
</pre></div>
</div>
</section>
<section id="operators">
<h2>Operators<a class="headerlink" href="#operators" title="Link to this heading">¶</a></h2>
<p>The following operators are available in VCL. See the examples further
down for, uhm, examples.</p>
<dl class="simple">
<dt>=</dt><dd><p>Assignment operator.</p>
</dd>
</dl>
<dl class="simple">
<dt>==</dt><dd><p>Comparison.</p>
</dd>
</dl>
<dl class="simple">
<dt>~</dt><dd><p>Match. Can either be used with regular expressions or ACLs.</p>
</dd>
</dl>
<dl class="simple">
<dt>!</dt><dd><p>Negation.</p>
</dd>
</dl>
<dl class="simple">
<dt>&amp;&amp;</dt><dd><p>Logical <em>and</em></p>
</dd>
</dl>
<dl class="simple">
<dt>||</dt><dd><p>Logical <em>or</em></p>
</dd>
</dl>
</section>
<section id="built-in-subroutines">
<h2>Built in subroutines<a class="headerlink" href="#built-in-subroutines" title="Link to this heading">¶</a></h2>
<p>Varnish has quite a few built-in subroutines that are called for each
transaction as it flows through Varnish. These built-in subroutines are
all named <code class="docutils literal notranslate"><span class="pre">vcl_*</span></code> and are explained in <a class="reference internal" href="../reference/vcl-step.html#id7"><span class="std std-ref">VCL Steps</span></a>.</p>
<p>Processing in built-in subroutines ends with <code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">(&lt;action&gt;)</span></code>
(see <a class="reference internal" href="../reference/vcl-step.html#vcl-actions"><span class="std std-ref">VCL Actions</span></a>).</p>
<p>The <a class="reference internal" href="vcl-built-in-code.html#vcl-built-in-code"><span class="std std-ref">Built-in VCL</span></a> also contains custom assistant subroutines
called by the built-in subroutines, also prefixed with <code class="docutils literal notranslate"><span class="pre">vcl_</span></code>.</p>
</section>
<section id="custom-subroutines">
<h2>Custom subroutines<a class="headerlink" href="#custom-subroutines" title="Link to this heading">¶</a></h2>
<p>You can write your own subroutines, whose names cannot start with <code class="docutils literal notranslate"><span class="pre">vcl_</span></code>.</p>
<p>A subroutine is typically used to group code for legibility or reusability:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">sub</span> <span class="n">pipe_if_local</span> <span class="p">{</span>
  <span class="k">if</span> <span class="p">(</span><span class="n">client</span><span class="o">.</span><span class="n">ip</span> <span class="o">~</span> <span class="n">local</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">return</span> <span class="p">(</span><span class="n">pipe</span><span class="p">);</span>
  <span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
<p>To call a subroutine, use the <code class="docutils literal notranslate"><span class="pre">call</span></code> keyword followed by the
subroutine’s name:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">call</span> <span class="n">pipe_if_local</span><span class="p">;</span>
</pre></div>
</div>
<p>Custom subroutines in VCL do not take arguments, nor do they return
values.</p>
<p><code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">(&lt;action&gt;)</span></code> (see <a class="reference internal" href="../reference/vcl-step.html#vcl-actions"><span class="std std-ref">VCL Actions</span></a>) as shown in
the example above returns all the way from the top level built in
subroutine (see <a class="reference internal" href="../reference/vcl-step.html#id7"><span class="std std-ref">VCL Steps</span></a>) which, possibly through
multiple steps, lead to the call of the custom subroutine.</p>
<p><code class="docutils literal notranslate"><span class="pre">return</span></code> without an action resumes execution after the <code class="docutils literal notranslate"><span class="pre">call</span></code>
statement of the calling subroutine.</p>
</section>
</section>

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    <ul>
<li><a class="reference internal" href="#">VCL Syntax</a><ul>
<li><a class="reference internal" href="#strings">Strings</a></li>
<li><a class="reference internal" href="#access-control-lists-acls">Access control lists (ACLs)</a></li>
<li><a class="reference internal" href="#operators">Operators</a></li>
<li><a class="reference internal" href="#built-in-subroutines">Built in subroutines</a></li>
<li><a class="reference internal" href="#custom-subroutines">Custom subroutines</a></li>
</ul>
</li>
</ul>

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