Syntax

PHP tags

PHP code must be put between some special characters

<?php     ?>
<?        ?>    // with short_open_tag enabled or php with option --enable-short-tags
<script language="php"> </script>  // old style
<%        %>    // ASP style asp_tags enabled

Other formats

<?php echo 'message'; ?>   // this are equivalents
<?= 'message'; ?>     // if short_open_tag is enabled or PHP > 5.4
<%= 'message'; ?>   // if asp_tags is enabled

PHP blocks mixed with HTML code

<?php if ($expression == true): ?>
  Text if true <img src="/image.jpg" />
<?php else: ?>
  HTML code for else <a href="/branch.html">branch</a>.
<?php endif; ?>

Some exceptions

<?php echo '<?xml version="1.0" encoding="UTF-8" ?>'; ?>
// xml files must start with this to be PHP compatible

<?php // not allowed as the only text in PHP 5.2 or less

Best practice

  ?>  // don't use ending tags in php only files to prevent sending headers if you put a space after ?>

<?= 'text'; ?>  // not recomanded for redistributable code or changing environments

Comments

Single line comments

<?php // comment ?>
<?php # comment ?>

<?php // comment ends at the end of the line
      //  or at ending tag ?>   here is outside comment

<script language="php"> //this comment doesn't end at script tag ending </scrip>

Multiline comments

<?php /*  starts here
          continues here
          ends here     */   ?>

Comments mistakes

<?php
       //echo '<?php code ?>'; ?>

<?php /*
      $pattern = "/^\d.*/";
      */

<?php
/*
      echo 'Some text'; /* Can't imbricate multiline comments */
*/