Nick Sdk

<?php
$fileName = 'fileName.txt';
$doubles = [
    'withRegister' => [],
    'withoutRegister' => [],
];

$fileHandle = fopen($fileName, "r");
if ($fileHandle) {
    while (($line = fgets($fileHandle)) !== false) {
        $lineWithoutRegister = mb_strtolower($line);
        if (!isset($doubles['withRegister'][$line])) {
            $doubles['withRegister'][$line] = 0;
        }
        if (!isset($doubles['withoutRegister'][$lineWithoutRegister])) {
            $doubles['withoutRegister'][$lineWithoutRegister] = 0;
        }
        $doubles['withRegister'][$line]++;
        $doubles['withoutRegister'][$lineWithoutRegister]++;

    }
    fclose($fileHandle);
} else {
    throw new Exception('Error read file.');
}
echo "\nДубли с учетом регистра:\n";
foreach ($doubles['withRegister'] as $line => $count) {
    if ($count > 1) {
        echo "{$count} дублей:\n{$line}\n";
    }
}
echo "\nДубли без учета регистра:\n";
foreach ($doubles['withoutRegister'] as $line => $count) {
    if ($count > 1) {
        echo "{$count} дублей:\n{$line}\n";
    }
}