1 Basic PHP syntax

PHP tags

1 when parsing a file, PHP looks for the start and end tags, that is, <?php and, and any parts outside the start and end tags will be ignored by the PHP parser.

2 PHP also allows the use of short mark <? And, but not encouraged to use. Short marks can be used only by activating the Short_open_tag configuration directive in php.ini or by using the configuration option--enable-short-tags when compiling PHP.

3 If the file content is pure PHP code, it is best to remove the PHP end tag at the end of the file. This avoids having to accidentally add a space or line break after the PHP end tag, causing PHP to start outputting these blanks, and there is no intent to output at this time in the script.

<?phpecho "Hello World";

Detach from HTML

1 anything outside a pair of start and end tags is ignored by the PHP parser, which allows the PHP file to have mixed content. You can embed PHP in an HTML document.

<p>html content </p><?= "Hello world";? ><p>html content </p>

Four pairs of different start and end tags

1 <?php?> is always available

<?php Echo ' Hello world ';?>

2 <script language= "PHP" > </script> always available

<script language= "php" >echo ' Hello World ';</script>

3 short mark. The directive Short_open_tag in the PHP.ini configuration file is available only after it is opened, or the--enable-short-tags option is added when PHP is compiled.

<?php $HW = "Hello world";? ><? echo $hw; ><?= $hw;? >

4 ASP style tag. It is only available after the instruction Asp_tags in the php.ini configuration file is opened (usually deprecated).
<?php $HW = "Hello World";?>
<% Echo $HW; %>
<%= $HW%>

Attention:
1 because the server may not support short tags. for porting and distributing code, make sure that you do not use short tags.
2 PHP 5.2 and previous versions, the interpreter does not allow the entire contents of a file to be a start tag <?php. This file is allowed from PHP 5.3, but there is one or more white space characters after the start tag.
3 from PHP 5.4, the short-form echo tag <?= is always recognized and valid, regardless of the Short_open_tag setting.

Instruction delimiter:
The end tag in the 11-segment PHP code implicitly represents a directive delimiter: semicolon.
2 The last line in a PHP code snippet can end without a semicolon.
3 The last line is omitted, the semicolon cannot be omitted.

<?phpecho "Hello World";//semicolon? ><?php echo "Hello World"//omit semicolon? ><?php echo ' Hello World ';//cannot omit

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1 Basic PHP syntax