(xemacs.info)Startup Paths


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3.3 How XEmacs finds Directories and Files
==========================================

XEmacs deals with a multitude of files during operation.  These files
are spread over many directories, and XEmacs determines the location of
most of these directories at startup and organizes them into various
paths.  (A "path", for the purposes of this section, is simply a list
of directories which XEmacs searches successively in order to locate a
file.)

3.3.1 XEmacs Directory Hierarchies
----------------------------------

Many of the files XEmacs looks for are located within the XEmacs
installation itself.  However, there are several views of what actually
constitutes the "XEmacs installation": XEmacs may be run from the
compilation directory, it may be installed into arbitrary directories,
spread over several directories unrelated to each other.  Moreover, it
may subsequently be moved to a different place.  (This last case is not
as uncommon as it sounds.  Binary kits work this way.)  Consequently,
XEmacs has quite complex procedures in place to find directories, no
matter where they may be hidden.

   XEmacs will always respect directory options passed to `configure'.
However, if it cannot locate a directory at the configured place, it
will initiate a search for the directory in any of a number of
"hierarchies" rooted under a directory which XEmacs assumes contain
parts of the XEmacs installation; it may locate several such hierarchies
and search across them.  (Typically, there are just one or two
hierarchies: the hierarchy where XEmacs was or will be installed, and
the one where it is being built.)  Such a directory containing a
hierarchy is called a "root".  Whenever this section refers to a
directory using the shorthand `<root>', it means that XEmacs searches
for it under all hierarchies XEmacs was able to scrounge up.  In a
running XEmacs, the hierarchy roots are stored in the variable
`emacs-roots'.  

3.3.2 Package Hierarchies
-------------------------

Many relevant directories and files XEmacs uses are actually not part of
the core installation.  They are part of any of the many packages
usually installed on top of an XEmacs installation.  (Note: Packages.)
Hence, they play a prominent role in the various paths XEmacs sets up.

   XEmacs locates packages in any of a number of package hierarchies.
Package hierarchies fall into three groups: "early", "late", and "last", according
to the relative location at which they show up in the various XEmacs
paths.  Early package hierarchies are at the very front, late ones
somewhere in the middle, and last hierarchies are (you guessed it) last.

   By default, XEmacs expects an early package hierarchy in the
subdirectory `.xemacs/xemacs-packages' of the user's home directory.

   Moreover, XEmacs expects late hierarchies in the subdirectories
`site-packages', `mule-packages', and `xemacs-packages' (in that order)
of the `<root>/lib/xemacs' subdirectory of one of the installation
hierarchies.  (If you run in-place, these are direct subdirectories of
the build directory.)  Furthermore, XEmacs will also search these
subdirectories in the `<root>/lib/xemacs-<VERSION>' subdirectory and
prefer directories found there.

   By default, XEmacs does not have a pre-configured last package
hierarchy.  Last hierarchies are primarily for using package hierarchies
of outdated versions of XEmacs as a fallback option.  For example, it is
possible to run XEmacs 21 with the 20.4 package hierarchy as a last
hierarchy.

   It is possible to specify at configure-time the location of the
various package hierarchies with the `--package-path' option to
configure.  The early, late, and last components of the package path
are separated by double instead of single colons.  If all three
components are present, they locate the early, late, and last package
hierarchies respectively.  If two components are present, they locate
the early and late hierarchies.  If only one component is present, it
locates the late hierarchy.  At run time, the package path may also be
specified via the `EMACSPACKAGEPATH' environment variable.

   An XEmacs package is laid out just like a normal installed XEmacs
lisp directory.  It may have `lisp', `etc', `info', and `lib-src'
subdirectories.  XEmacs adds these at appropriate places within the
various system-wide paths.

   There may be any number of package hierarchy directories.

3.3.3 Directories and Paths
---------------------------

Here is a list of the various directories and paths XEmacs tries to
locate during startup.  XEmacs distinguishes between directories and
paths specific to "version", "site", and "architecture" when looking
for them.

`version-specific'
     directories are specific to the version of XEmacs they belong to
     and typically reside under `<root>/lib/xemacs-<VERSION>'.

`site-specific'
     directories are independent of the version of XEmacs they belong
     to and typically reside under `<root>/lib/xemacs'

`architecture-specific'
     directories are specific both to the version of XEmacs and the
     architecture it runs on and typically reside under
     `<root>/lib/xemacs-<VERSION>/<ARCHITECTURE>'.

   During installation, all of these directories may also reside
directly under `<root>', because that is where they are in the XEmacs
tarball.

   If XEmacs runs with the `-debug-paths' option (Note: Command
Switches), it will print the values of these variables, hopefully
aiding in debugging any problems which come up.

`lisp-directory'
     Contains the version-specific location of the Lisp files that come
     with the core distribution of XEmacs.  XEmacs will search it
     recursively to a depth of 1 when setting up `load-path'.

`load-path'
     Is where XEmacs searches for XEmacs Lisp files with commands like
     `load-library'.  It contains the package lisp directories (see
     further down) and the version-specific core Lisp directories.  If
     the environment variable `EMACSLOADPATH' is set at startup, its
     directories are prepended to `load-path'.  

`Info-directory-list'
     Contains the location of info files.  (See Note: (info).)  It
     contains the package info directories and the version-specific core
     documentation.  Moreover, XEmacs will add `/usr/info',
     `/usr/local/info' as well as the directories of the environment
     variable `INFOPATH' to `Info-directory-list'.

`exec-directory'
     Is the directory of architecture-dependent files that come with
     XEmacs, especially executable programs intended for XEmacs to
     invoke.

`exec-path'
     Is the path for executables which XEmacs may want to start.  It
     contains the package executable paths as well as `exec-directory',
     and the directories of the environment variables `PATH' and
     `EMACSPATH'.  

`doc-directory'
     Is the directory containing the architecture-specific `DOC' file
     that contains documentation for XEmacs' commands.

`data-directory'
     Is the version-specific directory that contains core data files
     XEmacs uses.  It may be initialized from the `EMACSDATA' environment
     variable.

`data-directory-list'
     Is the path where XEmacs looks for data files.  It contains
     package data directories as well as `data-directory'.



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