SQL from Linux command line

Hello

Hoping for some help on this one....

I need to query postgres, run a count of *specific *records, and write to a
different table based on the results all from the linux command line.

This feels like it should be simple, but I'm new to postgres and could use
some help.

I'm good with the SQL part - for the SQL, I would write:

create table2 as select *, case when _cnt_ < 50 then 'low' when _cnt_ >= 50
'high' end as cnt from (select id, count(*) as _cnt_ from table1 where id =
1234 group by id) a;

My questions are:

1. Would I use psql for this?
2. If so, how do I structure the script to run psql from Linux?
3. how do I pass the value for the where clause from the command line
into the code?

Thanks!

Scott