20060922.2044

Git Configuration Hierarchy
===========================
Copyright (C) 2006 by Raymond S Brand

Note: This applies to more than Git, but it was written with Git in
mind.

The settings for the runtime configuration of a tool may be found in
several locations and each of those locations may be part of a different
administrative domain. The tool user desires that the tool behaves in a
predictable and consistent fashion which implies that the relative
priority and/or search order of configuration sources should be well
specified.


Configuration Sources
---------------------
The following is a list of generic locations where a tool may find
runtime configuration. Not all tools will search in all the listed
locations and tools may search in locations not listed. The list is
ordered from the least amount of information available about a specific
tool use to the most amount of information available about a specific
tool use.

A tool may search for runtime configuration in any order.  However, a
tool user expects that each of the individual runtime configuration
settings used by the tool to be from the configuration source that
specifies the individual runtime configuration setting with the most
amount of information available about the specific tool use.

Tools may also alter the configuration search strategy or locations due
to command line options, environment variables, or other configuration
locations.


Default Settings in the Source Code:
	Behavior of the tool in the absence of other configuration
	information. Behavior should default to something safe and
	likely to work.

	Unix Example:
		Not using a pager process for command output.

	Git Example:
		Committer identification is taken from the GCOS field of
		the system passwd file and the hostname.

Build Time Settings:
	Default tool behaviors that are dependent on how the tool was
	built.

	Unix Example:
		System directory path separator.

	Git Example:
		NO_SYMLINK_HEAD.

Installation Time Settings:
	Default tool behaviors that are dependent on where the tool is
	installed.

	Unix Example:
		Paths to supporting utilities.

	Git Example:
		None.

System General Settings:
	Configuration defaults for all users on the system.

	Unix Example:
		Setting $PATH in /etc/profile.

	Git Example:
		Default hook scripts in the Git (system) templates
		directory.

User General Settings:
	Configuration information for a particular user to apply to all
	uses of the tool by that user.

	Unix Example:
		Many of the "dot" files in a user's home directory.

	Git Example:
		$HOME/.gitconfig.

Project General Settings:
	Configurable behavior that all project participants should
	conform to.

	Unix Example:
		The, sometimes complex, machinery implemented in
		Makefiles of some projects.

	Git Example:
		Scripts in $GIT_DIR"/hooks/ can be used for this but
		there is no native support for maintaining consistency
		across all participants.	

User Project Settings:
	Configuration information for a particular user that is specific
	to a particular project.

	Unix Example:

	Git Example:
		$GIT_DIR/config

Environment Variables:
	Configuration information that only applies to commands executed
	by a particular process or process' inheriting the environment
	of that process.

	Unix Example:
		$PAGER

	Git Example:
		$GIT_COMMITTER_NAME

Command Line Options:
	Configuration information that only applies to a particular
	command invocation.

	Unix Example:
		The "-e" option to sh or bash.

	Git Example:
		The "--author" option to git-commit.