db.php

<?php
class db
{
    private $_dsn = '';
    private $_username = null;
    private $_password = null;
    private $_pdo = null;

    public function __construct($cli)
    {
        if (preg_match('/^mysql /', $cli)) {
            $args = explode(' ', $cli);
            $shortopts = ['D', 'h', 'p', 'P', 'u'];
            $longopts = ['database', 'host', 'password', 'port', 'user',
                         'default-character-set'];
            $params = $this->_parseOpts($args, $shortopts, $longopts);
            if (!isset($params['database']) && isset($args[0])) {
                $params['database'] = $args[0];
            }
            if (!isset($params['database'])) {
                throw new Exception('MySQL: required database');
            }
            $this->_dsn = 'mysql:dbname=' . $params['database'];
            if (isset($params['host'])) {
                $this->_dsn .= ';host=' . $params['host'];
            }
            if (isset($params['port'])) {
                $this->_dsn .= ';port=' . $params['port'];
            }
            if (isset($params['default-character-set'])) {
                $this->_dsn .= ';charset=' . $params['default-character-set'];
            }
            if (isset($params['user'])) {
                $this->_username = $params['user'];
            }
            if (isset($params['password'])) {
                $this->_password = $params['password'];
            }
        } else if (preg_match('/^psql /', $cli)) {
            $args = explode(' ', $cli);
            $shortopts = ['d', 'h', 'p', 'U', 'W'];
            $longopts = ['dbname', 'host', 'port', 'username', 'password'];
            $params = $this->_parseOpts($args, $shortopts, $longopts);
            if (!isset($params['dbname']) && isset($args[0])) {
                $params['dbname'] = $args[0];
            }
            if (!isset($params['username']) && isset($args[1])) {
                $params['username'] = $args[1];
            }
            if (!isset($params['dbname'])) {
                throw new Exception('PostgreSQL: required dbname');
            }
            $this->_dsn = 'pgsql:dbname=' . $params['dbname'];
            if (isset($params['host'])) {
                $this->_dsn .= ';host=' . $params['host'];
            }
            if (isset($params['port'])) {
                $this->_dsn .= ';port=' . $params['port'];
            }
            if (isset($params['username'])) {
                $this->_username = $params['username'];
            }
            if (isset($params['password'])) {
                $this->_password = $params['password'];
            }
        } else {
            throw new Exception('invalid command');
        }
    }

    private function _parseOpts(&$args, $shortopts, $longopts)
    {
        $params = [];
        $count = count($args);

        for ($i = 0; $i < $count; $i++) {
            if (strncmp($args[$i], '--', 2) == 0) {
                $key = substr($args[$i], 2);
                if (($n = array_search($key, $longopts)) === false) {
                    throw new Exception("invalid parameter: ${key}");
                }
            } else if (strncmp($args[$i], '-', 1) == 0) {
                $key = substr($args[$i], 1);
                if (($n = array_search($key, $shortopts)) === false ||
                    !isset($longopts[$n])) {
                    throw new Exception("invalid short parameter: $key");
                }
            } else {
                continue;
            }
            $val = $args[++$i];
            $params[$longopts[$n]] = $val;
            unset($args[$i]);
            unset($args[$i-1]);
        }

        array_shift($args);

        return $params;
    }

    private function _connect()
    {
        if ($this->_pdo === null) {
            $this->_pdo = new PDO($this->_dsn,
                                  $this->_username, $this->_password);
        }
        return $this->_pdo;
    }

    public function execute($sql)
    {
        if (empty($sql) || !is_string($sql)) {
            throw new Exception('invalid SQL string');
        }

        $stmt = $this->_connect()->prepare($sql);

        $args = func_get_args();
        array_shift($args);

        $stmt->execute($args);

        return $stmt->fetchAll(PDO::FETCH_ASSOC);
    }
}