What are the common regular expressions in PHP programming?

PHP, as a common server-side programming language, often needs to use regular expressions in development. Regular expression is a tool used to match strings. It uses specific grammatical rules to describe the pattern of a string and can better handle string matching, search, replacement and other operations.

The following lists common regular expressions in PHP programming:

1. Matching email addresses
   In development, it is often necessary to verify whether the email address entered by the user is legal. The following is a Regular expression for matching email addresses:

$regex = "/^w+([.-]?w+)*@w+([.-]?w+)*(.w{2,3})+$/";

You can use the preg_match() function to verify it. Use:

$email = 'test@example.com';
if (preg_match($regex, $email)) {
    echo 'Valid email address';
} else {
    echo 'Invalid email address';
}

2. Match URL address
   Same as verifying whether the URL address is legal It is also a common requirement. The following is a regular expression for matching URL addresses:

$regex = "/^(http|https|ftp)://([A-Z0-9][A-Z0-9_-]*(?:.[A-Z0-9][A-Z0-9_-]*)+):?(d+)?/?/i";

You can also use the preg_match() function for verification:

$url = 'http://www.example.com';
if (preg_match($regex, $url)) {
    echo 'Valid URL';
} else {
    echo 'Invalid URL';
}

3. Matches phone numbers
   It is also a common requirement to verify whether the phone number is legal. The following is a regular expression for matching phone numbers:

$regex = "/^[0-9]{3}-?[0-9]{3}-?[0-9]{4}$/";

You can also use the preg_match() function for verification:

$phone = '555-555-5555';
if (preg_match($regex, $phone)) {
    echo 'Valid phone number';
} else {
    echo 'Invalid phone number';
}

4. Check whether it contains text
   Sometimes you need to determine whether a string contains a certain keyword. The following is a regular expression that matches a certain keyword:

$regex = "/keyword/i";

Similarly You can use the preg_match() function for verification:

$string = 'This is a text with keyword in it';
if (preg_match($regex, $string)) {
    echo 'Keyword found';
} else {
    echo 'Keyword not found';
}

5. Matching HTML tags
   When processing HTML text, you need to match information such as tag names and attributes. The following is a matching HTML tag name and attribute Regular expression:

$regex = "/<(w+)([^>]+)*>/i";

You can also use the preg_match() function for verification:

$html = '<div class="example">Hello World</div>';
if (preg_match($regex, $html, $match)) {
    echo 'Tag name: ' . $match[1];
    echo 'Tag attributes: ' . $match[2];
} else {
    echo 'HTML tag not found';
}

Summary: Regular expression is a very important tool in PHP programming and is a common application There are verification email addresses, URL addresses, phone numbers, etc., and can also be used to check whether a certain keyword is included and matching HTML tags, etc. Mastering the basic syntax and common functions of regular expressions can improve program development efficiency and code readability.

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