array_push() / array_pop() / array_shift() / array_unshift() Since: PHP 4（2000）

// Adds one or more elements to the end of an array.
array_push(array, value1, value2, ...);

// Removes and returns the last element of an array.
array_pop(array);

// Removes and returns the first element of an array.
array_shift(array);

// Adds one or more elements to the beginning of an array.
array_unshift(array, value1, value2, ...);

<?php
$fruits = ['apple', 'orange', 'grape'];

// Add elements to the end.
array_push($fruits, 'peach', 'strawberry');
print_r($fruits); // Results in ['apple', 'orange', 'grape', 'peach', 'strawberry'].

// Remove the last element.
$last = array_pop($fruits);
echo $last; // Outputs 'strawberry'.

// Remove the first element.
$first = array_shift($fruits);
echo $first; // Outputs 'apple'.

// Add elements to the beginning.
array_unshift($fruits, 'melon', 'watermelon');
print_r($fruits); // Results in ['melon', 'watermelon', 'orange', 'grape', 'peach'].

// You can also use $fruits[] to append to the end.
$fruits[] = 'banana';
print_r($fruits); // 'banana' is added to the end.

array_push() and array_pop() operate on the end of an array, while array_unshift() and array_shift() operate on the beginning. By combining these, you can implement stack and queue behavior.

When you only need to append a single element, the $array[] = $value syntax is simpler and faster. Use array_push() when you want to add multiple values at once.

When array_shift() is called, the remaining numeric keys are re-indexed starting from zero. String keys are preserved, so be aware of key changes when using it with associative arrays. To manipulate elements at an arbitrary position, use array_splice().