Script checking to see what database it's connected to

Postgresql 12.5

I've got scripts which can run on multiple database (dev, test, QA,
Integration, Training, etc, etc), so of course I've got to run them like
"psql my_db_name -f script.sql".

Of course, I sometimes forget to specify the database name, and so it fails.

Thus, I want to add a bit to the top of the script, something like this:

\if :DBNAME = postgres
    echo "must not run in postgres"
    exit
\endif

However, I can't seem to find the magic sauce.

This is what I've tried so far:

postgres=# \if :DBNAME == postgres
unrecognized value "postgres == postgres" for "\if expression": Boolean expected
postgres(at)#

postgres=# \if ':DBNAME' == postgres
unrecognized value ":DBNAME == postgres" for "\if expression": Boolean expected
postgres(at)#

postgres=# \if :DBNAME == 'postgres'
unrecognized value "postgres == postgres" for "\if expression": Boolean expected
postgres(at)#

postgres=# \if ':DBNAME' == 'postgres'
unrecognized value ":DBNAME == postgres" for "\if expression": Boolean expected
postgres(at)#

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