plpgsql and escape

hi all!
i'm trying to do this ( converting unix time to human readable time in another table )

create function align_vs() returns opaque as
'
        declare
                line_vs vs%ROWTYPE;
                itime vs.step_time%TYPE;
        begin

        itime := to_char( timestamp ''epoch'' + interval ''NEW.step_time seconds'', ''YYYY-MM-DD HH24:MI:SS'' );
        update vs set w_id = NEW.w_id, step_id = %NEW.step_id, step_time = itime where w_id = NEW.w_id;

        return null;
end;
' language plpgsql;

the double ' around NEW.step_time blocks its interpolation. which is the correct escaping sintax here?

TIA
Ivan

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