Use PostgreSQL psql client from within Atom
currently run only in Linux and Mac.
In order to start use: F9 or menu: "Packages -> atom-psql -> new Connection"
for demosntration of \gset you can try:
SELECT 1 as v1, now() \gset r_ SELECT :r_v1 + 1 as sum1 \gset SELECT :sum1 + 1 as sum2;
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.