psql's default database on connect (our internal ref. SRP-30861)

Hello,

testpos@srap53dxr1:~> psql --help
  ...
  -d, --dbname=DBNAME      database name to connect to (default: "testpos")

testpos@srap53dxr1:~> whoami
testpos

testpos@srap53dxr1:~> env | grep PG
PGPASSWORD=xxxxxxxx
PGHOST=localhost
PGPORT=5432

testpos@srap53dxr1:~> LANG=C psql -Usisis
psql (13.3)
Type "help" for help.

sisis=# \l
                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   
-----------+----------+----------+-------------+-------------+-----------------------
 postgres  | postgres | UTF8     | de_DE.UTF-8 | de_DE.UTF-8 | 
 sisis     | sisis    | UTF8     | de_DE.UTF-8 | de_DE.UTF-8 | 
 ...

Why psql connects to the database 'sisis'? I was expecting that it
will try to connect to a database 'testpos' as this is the UNIX login
and as '-d....' was not specified. I was expecting in this case an
error like this:

testpos@srap53dxr1:~> export PGDATABASE=testpos
testpos@srap53dxr1:~> psql -Usisis
psql: error: FATAL:  database »testpos« does not exist

What do I uderstand wrong?

    matthias
-- 
Matthias Apitz, ✉ guru@unixarea.de, http://www.unixarea.de/ +49-176-38902045
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