In order to satisfy the requirement of easy examination by tools, there will be exactly one file located at a fixed spot. Under Unix, this fixed spot is naturally the /etc/ directory, where most configuration data resides. A subdirectory is used because we'll put more over here later in this document. The contents of the file should be minimal and easily parsed by scripts.
The format of the file is straightforward:
Lines are either empty lines, comment lines (starting with a hash mark (#)), or assignments;
Assignments take the form of "variable=right_hand_side", where whitespace is not allowed around the assignment operator. This makes the format Bourne-shell includable.
The SGML_BASE_DIR variable contains the directory name of the root of the location of sgml components. The suggested value for this variable is /usr/share/sgml.
The SGML_EXTRA_BASE_DIRS variable contains the directory name(s) of the root of the location(s) of optional sgml components, that the maintainer of the system doesn't want to install in the SGML_BASE_DIR directory. The suggested values for this variable are /usr/local/share/sgml or /opt/sgml/share. If multiple directory names are mentioned, they are separated by colons.
The SGML_BIN_DIR variable contains the directory where executables should be placed. This directory should occur in the default PATH of users of SGML components. The suggested value for this variable is /usr/bin although administrators may opt to use something like /usr/bin/sgml.
The SGML_EXTRA_BIN_DIRS variable contains the directory(s) where optional executables should be located. The suggested value for this varialble is /usr/local/bin or /opt/sgml/bin. If multiple directory names are mentioned, they are separated by colons.
A hint to components where to put temporary files. The suggested and default value for this variable is /tmp.
A command that is to be executed after new components have been installed. See also the section on catalog files, below.