PHP

Metacharacters

Metracharacters are special symbols that have a meaning beyond their literal value. They allow you to control the search pattern in some way (e.g., finding a pattern only at the beginning of the line). They will lose their special meaning if preceded with a backslash.

Character	Meaning
\	Escape character
^	Indicates the beginning of a string
$	Indicates the end of a string
.	Any single character except newline
\|	Alternatives (or)
[	Start of a v
]	End of a class
(	Start of a subpattern
)	End of a subpattern
{	Start of a quantifier
}	End of a quantifier

The first type of character you will use for defining a pattern is literal. A literal is a value that is written excatly as it is interpreted. Along with literals, your patterns will use metacharacters. The most important of which are the caret (^) and the dollar sign ($).

<html>
<head>
<title>PHP</title>
<meta Name="Author" Content="Hann So">
</head>
<body>
<p>
<?php
if (isset($_POST['submit'])) {
		process_form();
	}
	else {
		display_form();// display form for the first time
	}

function display_form() {
echo <<<HTML
	<form action = "$_SERVER[SCRIPT_NAME]" method="post">
	Regular Expression Pattern (include the delimiter):<br />
	<input type="text" name="pattern" value="/^world/" /><br />
	Text:<br />
	<textarea name="text" rows="5" cols="50">
	Welcome to the world of PHP. The Internet world is full of challenges.
	</textarea><br />
	<input type="submit" name="submit" value="Check" />
	</form>
	<table border>
	<tr bgcolor="lightcyan">
	<th align="left">Regular Expression</th>
	<th align="left">Text</th>
	</tr>
	<tr>
	<td>/^... /
	<br />(Go to the beginning (^) of the line and find any 3 characters, followed by a space.)
	</td>
	<td>red apple 0.50
	green apple 0.45
	fuji apple 0.65
	</td>
	</tr>
	</table>
HTML;
}

function process_form() {
	// stripslashes and trim the strings
	$pattern = stripslashes(trim($_POST['pattern']));
	$text = trim($_POST['text']);
	echo "The result of checking <br /><font color=red>$pattern</font><br />
	against<br /><font color=red>$text</font><br /> is:<br />";
	// match the pattern
	if (preg_match($pattern, $text, $matches)) {
		echo "$pattern was matched. <br />";
	}
	else {
		echo "$pattern was not matched. <br />";
	}
	echo "<br />The matches array contains:<br />";
	foreach ($matches as $key =>$values) {
		echo $key, " => ", $values, "<br />";
	}
	echo "<br /><a href=\"$_SERVER[SCRIPT_NAME]\">Check again?</a>";

}
?>
</p>
</body>
</html>

View the effect