Regular expressions in PHP

function	description
`preg_match(regex, string)`	returns `true` if `string` matches `regex`
`preg_replace(regex, replacement, string)`	returns a new string with all substrings that match `regex` replaced by `replacement`
`preg_split(regex, string)`	returns an array of strings from given `string` broken apart using given `regex` as delimiter (like `explode` but more powerful)

The next exercise uses regular expressions. (lecture slides)

Exercise : Regex Images (by Jamie Pell)

The code for images.php displays all JPG images in the images/ folder. Modify it using regular expressions so that it will display only image file namess that match each of the following patterns: (sample solution)

files that contain the word "Abbath", case insensitively
files that begin with "Abbath" and end with either "cat", "dog", or "sheep"
files that end in a number, such as puppy0247.jpg
files that begin with a 4-letter sequence of As or Bs, such as "Abba" or "baBb"

(example output)

Exercise Solution

<?php
$folder = "images";
$images = glob("$folder/*.jpg");

$regex = "/abbath/i";       // contain "abbath", case insensitive

foreach ($images as $image) {
	if (preg_match($regex, $image)) {
		?>
		<img src="<?= $image ?>" alt="an awesome picture" />
		<?php
	}
}

// begin with "abbath" and end with "cat", "dog", or "sheep"
// $regex = "/^$folder\/abbath(.*)(dog|cat|sheep).jpg$/";  
// $regex = "/[0-9].jpg$/";   // end in a number
// $regex = "/^[ab]{4}/i";    // start with 4 As/Bs
?>