einfo
Provides the number of records indexed in each field of a given database, the date of the last update of the database, and the available links from the database to other Entrez databases.
TLDR
Print all database names
$ einfo -dbs
Print all information of the protein database in XML format
$ einfo -db [protein]
Print all fields of the nuccore database
$ einfo -db [nuccore] -fields
Print all links of the protein database
$ einfo -db [protein] -links
