Backend Interface (BKI) files are scripts that are input to the Postgres backend running in the special "bootstrap" mode that allows it to perform database functions without a database system already existing. BKI files can therefore be used to create the database system in the first place. initdb uses BKI files to do just that: to create a database system. However, initdb's BKI files are generated internally. It generates them using the files global1.bki.source and local1.template1.bki.source, which it finds in the Postgres "library" directory. They get installed there as part of installing Postgres. These .source files get build as part of the Postgres build process, by a build program called genbki. genbki takes as input Postgres source files that double as genbki input that builds tables and C header files that describe those tables.
Related information may be found in documentation for initdb, createdb, and the SQL command CREATE DATABASE.
The Postgres backend interprets BKI files as described below. This description will be easier to understand if the global1.bki.source file is at hand as an example. (As explained above, this .source file isn't quite a BKI file, but you'll be able to guess what the resulting BKI file would be anyway).
Commands are composed of a command name followed by space separated arguments. Arguments to a command which begin with a “$” are treated specially. If “$$” are the first two characters, then the first “$” is ignored and the argument is then processed normally. If the “$” is followed by space, then it is treated as a NULL value. Otherwise, the characters following the “$” are interpreted as the name of a macro causing the argument to be replaced with the macro's value. It is an error for this macro to be undefined.
Macros are defined using
define macro macro_name = macro_valueand are undefined using
undefine macro macro_nameand redefined using the same syntax as define.
Lists of general commands and macro commands follow.