PHP Regular Expression Functions

PHP Regular Expression Functions

PHP provides a variety of functions that allow you to use regular expressions.

Some common regexp functions are:

• preg_match() - Returns 1 if the pattern was found in the string and 0 if not
• preg_match_all() - Returns the number of times the pattern was found in the string
• preg_replace() - Returns a new string where the matched patterns is replaced with another string
• preg_split() - Splits a string into an array using matches of a regular expression as separators
• preg_grep() - Returns an array containing only elements from the input that match the given pattern

PHP preg_match() Function

The preg_match() function returns 1 if the pattern was found in the string, and 0 if not.

Example

Use a regular expression to do a case-insensitive search for "example" in a string:

$str = "Visit example.com";
$pattern = "/example/i";
echo preg_match($pattern, $str);

PHP preg_match_all() Function

The preg_match_all() function returns how many matches were found for a pattern in a string.

Example

Use a regular expression to do a case-insensitive count of the number of occurrences of "ain" in a string:

$str = "The rain in SPAIN falls mainly on the plains.";
$pattern = "/ain/i";
echo preg_match_all($pattern, $str);

PHP preg_replace() Function

The preg_replace() function replaces all the matches of the pattern in a string with another string.

Example

Use a case-insensitive regular expression to replace Microsoft with Example in a string:

$str = "Visit Microsoft!";
$pattern = "/microsoft/i";
echo preg_replace($pattern, "Example", $str);

PHP preg_split() Function

The preg_split() function splits a string into an array using matches of a regular expression as separators.

Example

Use preg_split() to split a string into its components:

$str = "This is a text";
$pattern = "/[\s:]/";
$components = preg_split($pattern, $str);
print_r($components);

PHP preg_grep() Function

The preg_grep() function returns an array containing only elements from the input that match the given pattern.

Example

Get items from an array that starts with "p":

$input = [
"Red",
"Pink",
"Green",
"Blue",
"Purple"
];

$result = preg_grep("/^p/i", $input);
print_r($result);

The preg_grep() function also has a third parameter PREG_GREP_INVERT which will invert the result and returns an array containing only elements outside the input that match the given pattern.

Example

Get items from an array that do not starts with "p":

$input = [
"Red",
"Pink",
"Green",
"Blue",
"Purple"
];

$result = preg_grep("/^p/i", $input, PREG_GREP_INVERT);
print_r($result);

Grouping

You can use parentheses ( ) to apply quantifiers to entire patterns. They also can be used to select parts of the pattern to be used as a match.

Example

Use grouping to search for the word "banana" by looking for ba followed by two instances of na:

$str = "Apples and bananas.";
$pattern = "/ba(na){2}/i";
echo preg_match($pattern, $str);

Complete RegExp Reference

For a complete reference, go to the Complete PHP Regular Expression Reference.

The reference contains descriptions and examples of all Regular Expression functions.