What happens when you run PSQL slash commands?

Running \? within a psql database gives a whole list of commands that come in handy when performing various kinds of tasks.

$ psql psql (13.0) Type "help" for help. wangonya=# \? General \copyright show PostgreSQL usage and distribution terms \crosstabview [COLUMNS] execute query and display results in crosstab \errverbose show most recent error message at maximum verbosity ..... 

But what are the queries executed when these commands run?

I was recently tasked to write a bash script that loops through every schema on a database and does a pg_dump on it for backup then uploads the backups to an external server.

Running \dn gives a list of schemas but it also gives the owners, which I didn't need in my case.

wangonya=# \dn  List of schemas Name | Owner --------+---------- public | wangonya x | wangonya y | wangonya (3 rows) 

I only needed the schema names so I had to look for a way to edit the query run by \dn to only return names.

From the psql docs:

-E
--echo-hidden

Echo the actual queries generated by \d and other backslash commands. You can use this to study psql's internal operations. This is equivalent to setting the variable ECHO_HIDDEN to on.

Running psql with the -E flag then running the /dn command gives this result:

$ psql -E wangonya-# \dn ********* QUERY ********** SELECT n.nspname AS "Name", pg_catalog.pg_get_userbyid(n.nspowner) AS "Owner" FROM pg_catalog.pg_namespace n WHERE n.nspname !~ '^pg_' AND n.nspname <> 'information_schema' ORDER BY 1; ************************** List of schemas Name | Owner --------+---------- public | wangonya x | wangonya y | wangonya (3 rows) 

With the underlying query executed on running the slash command, I was able to edit it get the desired result.