PHP preg_match and preg_match_all functions

Question

I would like to know what the preg_match and preg_match_all functions do and how to use them.

Answer 1

Both preg_match and preg_match_all functions in PHP use Perl compatible regular expressions.

You can watch this series to fully understand Perl compatible regular expressions: https://www.youtube.com/watch?v=GVZOJ1rEnUg&list=PLfdtiltiRHWGRPyPMGuLPWuiWgEI9Kp1w

preg_match($pattern, $subject, &$matches, $flags, $offset)

The preg_match function is used to search for a particular $pattern in a $subject string and when the pattern is found the first time, it stops searching for it. It outputs matches in the $matches, where $matches[0] will contain the text that matched the full pattern, $matches[1] will have the text that matched the first captured parenthesized sub-pattern, and so on.

Example of preg_match()

]+>(.*)]+>|U",
    "example: 
this is a test
",
    $matches
);

var_dump($matches);

Output:

array(2) {
  [0]=>
  string(16) "example: "
  [1]=>
  string(9) "example: "
}

preg_match_all($pattern, $subject, &$matches, $flags)

The preg_match_all function searches for all the matches in a string and outputs them in a multi-dimensional array ($matches) ordered according to $flags. When no $flags value is passed, it orders results so that $matches[0] is an array of full pattern matches, $matches[1] is an array of strings matched by the first parenthesized sub-pattern, and so on.

Example of preg_match_all()

]+>(.*)]+>|U",
    "example: 
this is a test
",
    $matches
);

var_dump($matches);

Output:

array(2) {
  [0]=>
  array(2) {
    [0]=>
    string(16) "example: "
    [1]=>
    string(36) "
this is a test
"
  }
  [1]=>
  array(2) {
    [0]=>
    string(9) "example: "
    [1]=>
    string(14) "this is a test"
  }
}