The psql --list command can be used to display the Postgres databases. Something like this should be returned.

~]# psql --username johndoe --dbname db001 --list
                                 List of databases
   Name    |  Owner   | Encoding |  Collate   |   Ctype    |   Access privileges   
-----------+----------+----------+------------+------------+-----------------------
 db001     | postgres | UTF8     | en_US.utf8 | en_US.utf8 | 
 db002     | john.doe | UTF8     | en_US.utf8 | en_US.utf8 |

The psql command with the \dt (describe table) command can be used to list the tables in a database. If using the default posgres user account, I typically go with the following command.

sudo -u postgres psql --command "\dt"

If you have created a user account, the -u or --username option and --password flag can be used.

psql --username johndoe --password --command "\dt"

Better yet, you can setup passwordless authentication using the hidden .pgpass file and then connect without the --password flag.

psql --username johndoe --dbname mydb --command "\dt"

If did not find any relations is returned, this means the database contains no tables.

~]# psql --username johndoe --dbname mydb --command "\dt"
Did not find any relations.

Something like this should be returned.

                   List of relations
 Schema |             Name              | Type  | Owner 
--------+-------------------------------+-------+-------
 public | table001                      | table | johndoe
 public | table002                      | table | johndoe
 public | table003                      | table | johndoe

Or, the -x or --expanded flag can be used for a different format output.

~]$ psql --username johndoe --dbname mydb --expanded --command "\dt"
List of relations
-[ RECORD 1 ]---
Schema | public
Name   | mytable
Type   | table
Owner  | johndoe