Find all combinations of pairs of elements

<?php
$line = trim(fgets(STDIN));
$nums = explode(' ', $line);

foreach ($nums as $i => $num1) {
    foreach ($nums as $j => $num2) {
        if ($i === $j) {
            continue;
        }

        echo $num1 . ' ' . $num2 . PHP_EOL;
    }
}