自定义函数-获取文件的前几行数据

/**
     * Method to tail (a few last rows) of a file.
     *
     * @param     $filename
     * @param int $lines
     * @param int $buffer
     *
     * @return string
     */
    public function tail($filename, $lines = 10, $buffer = 4096)
    {
        $f      = fopen($filename, 'rb');
        $output = '';

        fseek($f, -1, SEEK_END);

        if ("\n" != fread($f, 1)) {
            --$lines;
        }

        while (ftell($f) > 0 && $lines >= 0) {
            $seek = min(ftell($f), $buffer);
            fseek($f, -$seek, SEEK_CUR);
            $output = ($chunk = fread($f, $seek)).$output;
            fseek($f, -mb_strlen($chunk, '8bit'), SEEK_CUR);
            $lines -= substr_count($chunk, "\n");
        }

        while ($lines++ < 0) {
            $output = substr($output, strpos($output, "\n") + 1);
        }

        fclose($f);

        return $output;
    }`