Concatenating String Literals in pgsql

How does one concat string literals in pgsql ?

The compiler complains about the concat operator in the following code
fragment:

RAISE EXCEPTION
    ''SELECT DISTINCT "t1"."usesysid" '' ||
        ''INTO userID '' ||
        ''FROM "pg_user" AS "t1" '' ||
        ''WHERE "t1"."usename" = current_user '' ||
        ''NOT FOUND'';

Thanks in advance.

Raymond