Rule 30

r30.php

<?php
/**
 * Run it: php r30.php
 * Run it with a custom number of rows: php r30.php <number>
 * Have fun :)
 */

function createRows($numRows, $rule) {
    $getNextRow = function ($currRow) use ($rule) {
        $nextRow = [0, 0];
        for ($i = 1, $iMax = count($currRow) - 1; $i < $iMax; $i++) {
            $nextRow[] = $rule[$currRow[$i - 1] . $currRow[$i] . $currRow[$i + 1]];
        }
        array_push($nextRow, 0, 0);
        return $nextRow;
    };

    $rows[0] = [0, 0, 1, 0, 0];
    for ($i = 1; $i <= $numRows; $i++) {
        $rows[$i] = $getNextRow($rows[$i - 1]);
    }

    return $rows;
}

function displayRows($rows, $isDownwards, $micSleep) {
    $rowCount = count($rows);

    $getRow = function ($rows, $isDownwards) use ($rowCount) {
        if ($isDownwards === true) {
            for ($i = 0; $i < $rowCount; $i++) {
                yield [$i, $rows[$i]];
            }
        } else {
            for ($i = $rowCount - 1; $i >= 0; $i--) {
                yield [$i, $rows[$i]];
            }
        }
    };

    foreach ($getRow($rows, $isDownwards) as [$pad, $row]) {
        echo str_repeat(' ', $rowCount - $pad);
        foreach ($row as $cell) {
            echo $cell === 1 ? '█' : ' ';
        }
        echo PHP_EOL;
        usleep($micSleep);
    }
}

// https://en.wikipedia.org/wiki/Rule_30
const RULE_30 = [
    '111' => 0,
    '110' => 0,
    '101' => 0,
    '100' => 1,
    '011' => 1,
    '010' => 1,
    '001' => 1,
    '000' => 0,
];

$numRows = isset($argv[1]) && (int)$argv[1] > 0 && (int)$argv[1] <= 1000  ? (int)$argv[1] : 80;

$rows = createRows($numRows, RULE_30);
while (true) {
    displayRows($rows, true, 5000);
    displayRows($rows, false, 5000);
}

https://3v4l.org/bO716 if you're curious and lazy