Programming Tutorials

preg_split() and explode() in PHP

By: Andi, Stig and Derick in PHP Tutorials on 2008-11-23  

preg_split() can be used to split a string into substrings by using a regular expression match for the delimiters. PHP provides an explode() function that also splits strings, but explode() can only use a simple string as the delimiter. explode() is much faster than using a regular expression, so you might be better off using explode() when possible. A simple example of preg_splits()'s usage might be to split a string into the words it contains. See the following example:

<?php

$str = 'This is an example for preg_split().';
$words = preg_split('@[\W]+@', $str)
print_r($words);

?>

The script outputs

Array
(
[0] => This
[1] => is
[2] => an
[3] => example
[4] => for
[5] => preg_split
[6] =>
)

As you can see, the last element is empty. By default, the function returns empty elements, too. The character(s) before the end of the string are non-word characters so they act as a delimiter, resulting in an empty element. You can pass two more parameters to the preg_split() function: a limit and a flag. The "limit" parameter controls how many elements are returned before the splitting stops. In the preg_split() example, two elements are returned:

<?php
$str = 'This is an example for preg_split().';
$words = preg_split('@[\W]+@', $str, 2);
print_r($words);
?>

The output is

Array
(
[0] => This
[1] => is an example for preg_split().
)

In the next example, we use -1 as the limit. -1 means that there is no limit at all, and allows us to pass flags without shortening our output array. Three flags specify what is returned: PREG_SPLIT_NO_EMPTY. Prevents empty elements from ending up in the returned array:

<?php
$str = 'This is an example.';
$words = preg_split('@[\W]+@', $str, -1,
PREG_SPLIT_NO_EMPTY);
print_r($words);
?>

The script outputs

Array
(
[0] => This
[1] => is
[2] => an
[3] => example
)

PREG_SPLIT_DELIM_CAPTURE. Returns the delimiters itself, but only if the delimiters are surrounded by parentheses. We combine the flag with PREG_SPLIT_NO_EMPTY:

<?php
$str = 'This is an example.';
$words = preg_split('@([\W]+)@', $str, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
print_r($words);
?>

The script outputs

Array
([0] => This
[1] =>
[2] => is
[3] =>
[4] => an
[5] =>
[6] => example
[7] => .
)

PREG_SPLIT_OFFSET_CAPTURE. Specifies that the function return a two dimensional array containing both the text and the offset in the string where the element started. In this example, we combine all three flags:

<?php
$str = 'This is an example.';
$words = preg_split( '@([\W]+)@', $str, -1, PREG_SPLIT_OFFSET_CAPTURE |PREG_SPLIT_DELIM_CAPTURE |PREG_SPLIT_NO_EMPTY);
var_export($words);
?>

The script outputs (reformatted):

array (
0 => array ( 0 => 'This', 1 => 0 ),
1 => array ( 0 => ' ', 1 => 4 ),
2 => array ( 0 => 'is', 1 => 5 ),
3 => array ( 0 => ' ', 1 => 7 ),
4 => array ( 0 => 'an', 1 => 8 ),
5 => array ( 0 => ' ', 1 => 10 ),
6 => array ( 0 => 'example', 1 => 11 ),
7 => array ( 0 => '.', 1 => 18 ),
)