Quoted strings on CLI

Hi,

I just migrated from mysql and am running into an issue I found no solution for when researching. Using the web interface I can insert values that contain single-quotes. But using the CLI I found no way to select or insert single quotes:

PetWork=# select * from persons where firstname='\'Peter\'';
Invalid command \'';. Try \? for help.
PetWork-# select * from persons where firstname='\\'Peter\\'';
Invalid command \. Try \? for help.
PetWork-# select * from persons where firstname='\\\'Peter\\\'';
Invalid command \. Try \? for help.
PetWork-# select * from persons where firstname='\\\\'Peter\\\\'';
Invalid command \. Try \? for help.
PetWork-# select * from persons where firstname='\\\\'Peter\\\\'';

On different forums the solution suggested is to prepend backslashes. But it doesn't matter how many backslashes I prepend, it always fails. What does one have to do to achieve that?

Thanks for any help