opposite of split php code example

Example 1: php split string

<?php
// It doesnt get any better than this Example
$pizza  = "piece1 piece2 piece3 piece4 piece5 piece6";
$pieces = explode(" ", $pizza);
echo $pieces[0]; // piece1
echo $pieces[1]; // piece2

Example 2: split php

// split() function was DEPRECATED in PHP 5.3.0, and REMOVED in PHP 7.0.0.
// ALTERNATIVES: explode(), preg_split()

// explode()
// DESCRIPTION: Breaks a string into an array.
// explode ( string $separator , string $string , int $limit = PHP_INT_MAX ) : array
$pizza  = "piece1 piece2 piece3 piece4 piece5 piece6";
$pieces = explode(" ", $pizza);
echo $pieces[0]; // piece1
echo $pieces[1]; // piece2

// preg_split()
// DESCRIPTION: Split the given string by a regular expression.
// preg_split ( string $pattern , string $subject , int $limit = -1 , int $flags = 0 ) : array|false
$keywords = preg_split("/[\s,]+/", "hypertext language, programming");
print_r($keywords);
// output:
Array
(
    [0] => hypertext
    [1] => language
    [2] => programming
)