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  <refentry id="function.eval">
   <refnamediv>
    <refname>eval</refname>
    <refpurpose>Evaluate a string as PHP code</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>mixed</type><methodname>eval</methodname>
      <methodparam><type>string</type><parameter>code_str</parameter></methodparam>
     </methodsynopsis>
    <simpara>
     <function>eval</function> evaluates the string given in
     <parameter>code_str</parameter> as PHP code. Among other things,
     this can be useful for storing code in a database text field for
     later execution.
    </simpara>
    <simpara>
     There are some factors to keep in mind when using
     <function>eval</function>. Remember that the string passed must
     be valid PHP code, including things like terminating statements
     with a semicolon so the parser doesn't die on the line after the
     <function>eval</function>, and properly escaping things in
     <parameter>code_str</parameter>.
    </simpara> 
    <simpara>
     Also remember that variables given values under
     <function>eval</function> will retain these values in the main
     script afterwards.
    </simpara>
    <simpara>
     A <literal>return</literal> statement will terminate the evaluation of 
     the string immediately. As of PHP 4, <function>eval</function> returns
     &null; unless <literal>return</literal> is called in the evaluated
     code, in which case the value passed to <literal>return</literal> is
     returned. In case of a fatal error in the evaluated code,
     <function>eval</function> returns &false;.
     In PHP 3, <function>eval</function> does not return a value.
    </simpara>
    <para>
     <example>
      <title>
       <function>eval</function> example - simple text merge
      </title>
      <programlisting role="php">
<![CDATA[
<?php
$string = 'cup';
$name = 'coffee';
$str = 'This is a $string with my $name in it.';
echo $str. "\n";
eval("\$str = \"$str\";");
echo $str. "\n";
?>
]]>
      </programlisting>
      <para>
       The above example will show:
      </para>
      <screen>
<![CDATA[
This is a $string with my $name in it.
This is a cup with my coffee in it.
]]>
      </screen>
     </example>
    </para>
    &tip.ob-capture;
    <para>
     See also <function>call_user_func</function>.
    </para>
   </refsect1>
  </refentry>

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