Pattern Matching using PHP

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