PHP provides support for regular expressions (regex) through various functions that allow you to work with patterns and manipulate strings. Regular expressions are powerful tools for searching, matching, and manipulating text based on specific patterns. They are widely used for tasks such as validation, data extraction, and text manipulation.

Here are some common PHP functions used for regex:

1. preg_match():

- This function searches a string for a pattern and returns true if a match is found, otherwise false.

php
$string = 'Hello, world!';
if (preg_match('/\bHello\b/', $string)) {
    echo 'Match found!';
} else {
    echo 'No match found!';
}
// Output: Match found!

2. preg_match_all():

- Similar to `preg_match()`, but it finds all occurrences of the pattern in the string and returns an array of matches.

php
$string = 'Hello, Hello, world!';
if (preg_match_all('/\bHello\b/', $string, $matches)) {
    echo 'Matches found: ' . count($matches[0]);
} else {
    echo 'No matches found!';
}
// Output: Matches found: 2

3. preg_replace():

- This function searches a string for a pattern and replaces all occurrences of the pattern with a specified replacement.

php
$string = 'The quick brown fox jumps over the lazy dog.';
$newString = preg_replace('/fox/', 'cat', $string);
echo $newString;
// Output: The quick brown cat jumps over the lazy dog.

4. preg_split():

- This function splits a string into an array based on a given regex pattern.

php
$string = 'apple,orange,banana';
$fruits = preg_split('/,/', $string);
print_r($fruits);
// Output: Array ( [0] => apple [1] => orange [2] => banana )

5. preg_quote():

- This function escapes special characters in a string so it can be safely used as part of a regex pattern.

php
$specialChar = '+';
$escapedChar = preg_quote($specialChar);
echo $escapedChar; // Output: \+

These are just a few examples of PHP's regex functions. Regular expressions can become complex, but they are immensely powerful for handling string manipulation and pattern matching tasks in PHP. You can refer to PHP's documentation for more details and advanced usage of regular expressions in PHP.

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