geth attach only lets you use webjs methods at the moment. By using nodejs console with @parity/api package you can access parity methods.
Install package globally and launch concole :
$ npm install @parity/api
$ node
On node console use parity package :
>// import the actual Api class
>const Api = require("@parity/api");
>// do the setup
>const provider = new Api.Provider.Http('http://localhost:8545');
>const api = new Api(provider);
// eg. use api.parity.addReservedPeer method
>api.parity.addReservedPeer("enode://d64d5f74b1715c525dc88e87a52eca1574c09593ed29401d205ecfef9fbfe52fa308f966bab3a5966da1bb74212fecdb328cddceb572c38b536c597166784347@203080240034.static.ctinets.com:35423").then((data)=> {console.log(data)})
parity --geth. You can attach console to a vanilla parity without geth compatibility mode, at least in 1.6.5. – Mikko Ohtamaa Apr 11 '17 at 20:35Fatal: Unable to attach to remote geth: dial unix /Users/jikkujose/Library/Ethereum/geth.ipc: connect: no such file or directory. Do I need to specify custom path? – Jikku Jose Jun 19 '17 at 04:09geth attach. – q9f Jun 19 '17 at 08:01