language/basic-syntax.xml
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<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<chapter xml:id="language.basic-syntax" xmlns="http://docbook.org/ns/docbook">
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<chapter xml:id="language.basic-syntax" xmlns="http://docbook.org/ns/docbook" annotations="interactive">
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<title>Basic syntax</title>
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<sect1 xml:id="language.basic-syntax.phptags">
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<title>PHP tags</title>
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<para>
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When PHP parses a file, it looks for opening and closing tags, which are
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<literal><?php</literal> and <literal>?></literal> which tell PHP to
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start and stop interpreting the code between them. Parsing in this manner
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allows PHP to be embedded in all sorts of different documents, as
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everything outside of a pair of opening and closing tags is ignored by the
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PHP parser.
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When PHP processes a file, it recognizes the opening and closing
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tags, <literal><?php</literal> and <literal>?></literal>, to
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define the boundaries of PHP code execution. Content outside these
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tags is ignored by the PHP parser, allowing PHP to seamlessly embed
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in various document types.
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</para>
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<para>
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PHP includes a short echo tag <literal><?=</literal> which is a
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short-hand to the more verbose <code><?php echo</code>.
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A whitespace character (space, tab, or newline) must follow
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<literal><?php</literal> to ensure proper token separation.
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Omitting this whitespace will result in a syntax error.
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</para>
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<para>
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PHP also includes the short echo tag <literal><?=</literal>,
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which is shorthand for <code><?php echo</code>.
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</para>
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<para>
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<example>
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<title>PHP Opening and Closing Tags</title>
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<para>
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<note>
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<para>
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As short tags can be disabled it is recommened to only use the normal
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As short tags can be disabled it is recommended to only use the normal
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tags (<code><?php ?></code> and <code><?= ?></code>) to
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maximise compatibility.
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</para>
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</para>
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<para>
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If a file contains only PHP code, it is preferable to omit the PHP closing tag
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at the end of the file. This prevents accidental whitespace or new lines
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If a file ends with PHP code, it is preferable to omit the PHP closing tag
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at the end of the file. This prevents accidental whitespace or new lines
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being added after the PHP closing tag, which may cause unwanted effects
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because PHP will start output buffering when there is no intention from
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the programmer to send any output at that point in the script.
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<informalexample>
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</para>
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<para>
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<example>
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<title>PHP Code Only File</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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echo "Hello world";
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echo "Hello world\n";
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// ... more code
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echo "Last statement";
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echo "Last statement\n";
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// the script ends here with no PHP closing tag
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]]>
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</programlisting>
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</informalexample>
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</example>
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</para>
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</sect1>
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<title>Escaping from HTML</title>
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<para>
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Everything outside of a pair of opening and closing tags is ignored by the
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PHP parser which allows PHP files to have mixed content. This allows PHP
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PHP parser which allows PHP files to have mixed content. This allows PHP
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to be embedded in HTML documents, for example to create templates.
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<informalexample>
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</para>
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<para>
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<example>
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<title>Embedding PHP in HTML</title>
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<programlisting role="php">
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<![CDATA[
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<p>This is going to be ignored by PHP and displayed by the browser.</p>
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<p>This will also be ignored by PHP and displayed by the browser.</p>
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]]>
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</programlisting>
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</informalexample>
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</example>
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</para>
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<para>
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This works as expected, because when the PHP interpreter hits the ?> closing
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tags, it simply starts outputting whatever it finds (except for the
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immediately following newline - see
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<para>
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<example>
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<title>Example showing the closing tag encompasing the trailing newline</title>
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<title>Example showing the closing tag encompassing the trailing newline</title>
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<programlisting role="php">
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<![CDATA[
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<?php echo "Some text"; ?>
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</para>
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<para>
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Examples of entering and exiting the PHP parser:
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<informalexample>
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<example>
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<title>Examples of entering and exiting the PHP parser</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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echo 'This is a test';
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echo "This is a test\n";
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?>
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<?php echo 'This is a test' ?>
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<?php echo "This is a test\n" ?>
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<?php echo 'We omitted the last closing tag';
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<?php echo "We omitted the last closing tag\n";
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]]>
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</programlisting>
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</informalexample>
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</example>
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</para>
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<para>
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<note>
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<para>
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The closing tag of a PHP block at the end of a file is optional,
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<title>Comments</title>
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<para>
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PHP supports 'C', 'C++' and Unix shell-style (Perl style) comments. For example:
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<informalexample>
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</para>
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<para>
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<example>
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<title>Comments</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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echo 'This is a test'; // This is a one-line c++ style comment
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echo "This is a test\n"; // This is a one-line c++ style comment
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/* This is a multi line comment
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yet another line of comment */
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echo 'This is yet another test';
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echo 'One Final Test'; # This is a one-line shell-style comment
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echo "This is yet another test\n";
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echo "One Final Test\n"; # This is a one-line shell-style comment
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?>
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]]>
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</programlisting>
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</informalexample>
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</example>
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</para>
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<simpara>
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The "one-line" comment styles only comment to the end of
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<literal>//</literal> or <literal>#</literal> cannot influence that.
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</simpara>
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<para>
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<informalexample>
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<example>
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<title>One Line Comments</title>
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<programlisting role="php">
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<![CDATA[
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<h1>This is an <?php # echo 'simple';?> example</h1>
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<p>The header above will say 'This is an example'.</p>
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]]>
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</programlisting>
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</informalexample>
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</example>
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</para>
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<simpara>
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'C' style comments end at the first <literal>*/</literal> encountered.
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Make sure you don't nest 'C' style comments. It is easy to make this
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Make sure you don't nest 'C' style comments. It is easy to make this
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mistake if you are trying to comment out a large block of code.
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</simpara>
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<para>
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