databases list to file

Hello all,

I need to print to a file a simple list of all the databases on my
postgresql.

I need to do this from a shell script to be executed without human
intervention

I guess something like:

su postgres -c 'psql ...whatever.... > /tmp/my_databases.txt'

but I don't know exactly to what extent I can format the output of this
in order to simplify the parser that will read that file.

any suggestions ?

thank you

joao