- array_splice: documentation ( source)
- array_merge: documentation ( source)
- var_export: documentation ( source)
- max: documentation ( source)
<?php
$array = [1, 2, 3, 4];
$index = 2;
$value = 9;
$remains = array_splice($array, max(0, $index - 1));
var_export(
array_merge(
$array,
[$value],
$remains
)
);