Honestly, file processing in CL is limited. It can be done but why would
you? To do this requires you call another program. Before anyone differs
with me, remember that ALL commands call a program. Don't believe me? Try
DSPCMD IF. Whether or not IBM supplies the program is a different matter.
Now as to your solution...
You could use the RUNSQL command that came out with TR4 in 7.1 to create a
new file sorted in that order.
RUNSQL SQL('create table qtemp/crap as (
select * from erplxf/rco order by rrn(rco) desc)
then you could process that table.
CL doesn't yet support imbedded sql, (like rpg does). Otherwise you could
drop the create table and process that directly.