php-doc-en/reference/misc/functions/eval.xml
Christoph Michael Becker a0a0165e07 fixed #70929: create_function now throws ParseError
git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@338282 c90b9560-bf6c-de11-be94-00142212c4b1
2015-12-17 11:38:30 +00:00

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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.eval" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>eval</refname>
<refpurpose>Evaluate a string as PHP code</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>mixed</type><methodname>eval</methodname>
<methodparam><type>string</type><parameter>code</parameter></methodparam>
</methodsynopsis>
<para>
Evaluates the given <parameter>code</parameter> as PHP.
</para>
<caution>
<para>
The <function>eval</function> language construct is <emphasis>very dangerous</emphasis>
because it allows execution of arbitrary PHP code. <emphasis>Its use thus is
discouraged.</emphasis> If you have carefully verified that there is no other option
than to use this construct, pay special attention <emphasis>not to pass any user
provided data</emphasis> into it without properly validating it beforehand.
</para>
</caution>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>code</parameter></term>
<listitem>
<para>
Valid PHP code to be evaluated.
</para>
<para>
The code must not be wrapped in opening and closing
<link linkend="language.basic-syntax.phpmode">PHP tags</link>, i.e.
<literal>'echo "Hi!";'</literal> must be passed instead of
<literal>'&lt;?php echo "Hi!"; ?&gt;'</literal>. It is still possible to leave and
re-enter PHP mode though using the appropriate PHP tags, e.g.
<literal>'echo "In PHP mode!"; ?&gt;In HTML mode!&lt;?php echo "Back in PHP mode!";'</literal>.
</para>
<para>
Apart from that the passed code must be valid PHP. This includes that all statements
must be properly terminated using a semicolon.
<literal>'echo "Hi!"'</literal> for example will cause a parse error, whereas
<literal>'echo "Hi!";'</literal> will work.
</para>
<para>
A <literal>return</literal> statement will immediately terminate the
evaluation of the code.
</para>
<para>
The code will be executed in the scope of the code calling <function>eval</function>. Thus any
variables defined or changed in the <function>eval</function> call will remain visible after
it terminates.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
<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. As of PHP 7, if there is a
parse error in the evaluated code, <function>eval</function> throws a ParseError exception.
Before PHP 7, in this case <function>eval</function> returned
&false; and execution of the following code continued normally. It is
not possible to catch a parse error in <function>eval</function>
using <function>set_error_handler</function>.
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<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>
&example.outputs;
<screen>
<![CDATA[
This is a $string with my $name in it.
This is a cup with my coffee in it.
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
&note.language-construct;
&tip.ob-capture;
<note>
<para>
In case of a fatal error in the evaluated code, the whole script exits.
</para>
</note>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>call_user_func</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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