The document discusses PHP regular expression functions including preg_filter(), preg_grep(), preg_last_error(), preg_match(), preg_match_all(), preg_replace(), preg_replace_callback(), preg_replace_callback_array(), preg_split(), and preg_quote(). It provides examples of how to use each function, describing what each returns or does. It also covers regular expression modifiers, patterns, and metacharacters.

1. Pattern Matching
Jigar Makhija

2. PHP Regular Expression Introduction
• Regular expressions allow you to search for and replace
patterns in strings.

3. PHP Regular Expression Functions
PHP preg_filter() Function
• Returns a string or an array with pattern matches
replaced, but only if matches were found
<?php
$input = [
"It is 5 o'clock",
"40 days",
"No numbers here",
"In the year 2000"
];
$result = preg_filter('/[0-9]+/', '($0)',
$input);
print_r($result);
?>
O/P:
Array
(
[0] => It is (5) o'clock
[1] => (40) days
[3] => In the year
(2000)
)

4. PHP Regular Expression Functions
PHP preg_grep() Function
• Returns an array consisting only of elements from the
input array which matched the pattern.
<?php
$input = [
"Red",
"Pink",
"Green",
"Blue",
"Purple"
];
$result = preg_grep("/^p/i", $input);
print_r($result);
?>
O/P:
Array
(
[1] => Pink
[4] => Purple
)

5. PHP Regular Expression Functions
PHP preg_last_error()
Function
• Returns an error code
indicating the reason that
the most recent regular
expression call failed.
<?php
$str = 'The regular expression is invalid.';
$pattern = '/invalid//';
$match = @preg_match($pattern, $str, $matches);
if($match === false) {
// An error occurred
$err = preg_last_error();
if($err == PREG_INTERNAL_ERROR) {
echo 'Invalid regular expression.';
}
} else if($match) {
// A match was found
echo $matches[0];
} else {
// No matches were found
echo 'No matches found';
}
?>

6. PHP Regular Expression Functions
PHP preg_match() Function & PHP preg_match_all()
Function
• Finds the first match of a pattern in a string
<?php
$str = "Visit W3Schools";
$pattern = "/w3schools/i";
echo preg_match($pattern, $str);
?>
Finds all matches of a pattern in a string
<?php
$str = "The rain in SPAIN falls mainly on the plains.";
$pattern = "/ain/i";
if(preg_match_all($pattern, $str, $matches)) {
print_r($matches);
}
?>
Array
(
[0] => Array
(
[0] => ain
[1] => AIN
[2] => ain
[3] => ain
)
)

7. PHP Regular Expression Functions
PHP preg_replace() Function
• Returns a string where matches of a pattern (or an array
of patterns) are replaced with a substring (or an array of
substrings) in a given string
<?php
$str = 'Visit Microsoft!';
$pattern = '/microsoft/i';
echo preg_replace($pattern, 'W3Schools', $str);
?>
O/P:
Visit W3Schools!

8. PHP Regular Expression Functions
PHP preg_replace_callback() Function
• Given an expression and a callback, returns a string
where all matches of the expression are replaced with the
substring returned by the callback
<?php
function countLetters($matches) {
return $matches[0] . '(' . strlen($matches[0]) . ')';
}
$input = "Welcome to W3Schools.com!";
$pattern = '/[a-z0-9.]+/i';
$result = preg_replace_callback($pattern, 'countLetters',
$input);
echo $result;
?>
O/P:
Welcome(7) to(2) W3Schools.com(13)!

9. PHP Regular Expression Functions
PHP
preg_replace_callback_array()
Function
• Given an array associating
expressions with callbacks,
returns a string where all
matches of each expression are
replaced with the substring
returned by the callback
<?php
function countLetters($matches) {
return $matches[0] . '[' . strlen($matches[0]) . 'letter]';
}
function countDigits($matches) {
return $matches[0] . '[' . strlen($matches[0]) . 'digit]';
}
$input = "There are 365 days in a year.";
$patterns = [
'/b[a-z]+b/i' => 'countLetters',
'/b[0-9]+b/' => 'countDigits'
];
$result = preg_replace_callback_array($patterns, $inp
echo $result;
?>
O/P:
There[5letter] are[3letter] 365[3digit] days[4letter] in[2letter] a[1letter] year[4letter].

10. PHP Regular Expression Functions
PHP preg_split() Function
• Breaks a string into an array using matches of a regular
expression as separators
<?php
$date = "1970-01-01 00:00:00";
$pattern = "/[-s:]/";
$components = preg_split($pattern, $date);
print_r($components);
?>
Array
(
[0] => 1970
[1] => 01
[2] => 01
[3] => 00
[4] => 00
[5] => 00
)

11. PHP Regular Expression Functions
PHP preg_quote() Function
• Escapes characters that have a special meaning in
regular expressions by putting a backslash in front of
them
<?php
$search = preg_quote("://", "/");
$input = 'https://www.w3schools.com/';
$pattern = "/$search/";
if(preg_match($pattern, $input)) {
echo "The input is a URL.";
} else {
echo "The input is not a URL.";
}
?>
O/P:
The input is a URL.

12. Regular Expression Modifiers
Modifier Description
i Performs a case-insensitive search
m Performs a multiline search (patterns that search for the beginning or end of a string will
match the beginning or end of each line)
u Enables correct matching of UTF-8 encoded patterns
Regular Expression Patterns
Expression Description
[abc] Find one character from the options between the brackets
[^abc] Find any character NOT between the brackets
[0-9] Find one character from the range 0 to 9

13. Metacharacters
• Metacharacters are characters with a special meaning:
Metacharacter Description
| Find a match for any one of the patterns separated by | as in: cat|dog|fish
. Find just one instance of any character
^ Finds a match as the beginning of a string as in: ^Hello
$ Finds a match at the end of the string as in: World$
d Find a digit
s Find a whitespace character
b Find a match at the beginning of a word like this: bWORD, or at the end of a word like this:
WORDb
uxxxx Find the Unicode character specified by the hexadecimal number xxxx