where.php

<?php

$index = isset($argv[1]) ? $argv[1] : die("No input given\n");
$value = isset($argv[2]) ? $argv[2] : die("No input given\n");
$books = require_once __DIR__ . '/books.php';

/**
 * Exercise 4 - Write a script that will search the books array and find all entries where the field specified by $index
 * has the value of $value. Echo the id and title of each book that matches the given criteria.
 */

$list = [];

foreach ($books as $book) {
    foreach ($book as $k => $v) {
        $pos = strpos(strtolower($v), strtolower($value));
        if ($k == $index && $pos !== false) {
            $list[] = $book['id']; 
        }
    }
}

echo "You searched for {$index} and {$value}. We found:" . PHP_EOL;

foreach($list as $hit) {
    echo "Book id: " . $books[$hit]['id'] . ", by author " . $books[$hit]['author'] . PHP_EOL;
}