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comp.windows.x Frequently Asked Questions (FAQ) 2/7
Section - 39) How does Xt use environment variables in loading resources?

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	You can use several environment variables to control how resources are
loaded for your Xt-based programs -- XFILESEARCHPATH, XUSERFILESEARCHPATH, and
XAPPLRESDIR.  These environment variables control where Xt looks for
application-defaults files as an application is initializing.  Xt loads at
most one app-defaults file from the path defined in XFILESEARCHPATH and
another from the path defined in XUSERFILESEARCHPATH.

	XAPPLRESDIR existed in R3 and before.  As of R4, the Xt developers
added the more sophisticated *SEARCHPATH mechanism, but left XAPPLRESDIR in
place to avoid breaking existing software.

	Set XFILESEARCHPATH if software is installed on your system in such a
way that app-defaults files appear in several different directory
hierarchies.  Suppose, for example, that you are running Sun's Open Windows,
and you also have some R4 X applications installed in
/usr/lib/X11/app-defaults. You could set a value like this for
XFILESEARCHPATH, and it would cause Xt to look up app-defaults files in both
/usr/lib/X11 and /usr/openwin/lib (or wherever your OPENWINHOME is located):
	setenv XFILESEARCHPATH /usr/lib/X11/%T/%N:$OPENWINHOME/lib/%T/%N

The value of this environment variable is a colon-separated list of
pathnames.  The pathnames contain replacement characters as follows (see
XtResolvePathname()):

	%N      The value of the filename parameter, or the
		application's class name.  
	%T      The value of the file "type".  In this case, the
		literal string "app-defaults" 
	%C      customization resource (R5/R6 only) 
	%D	site default value for XFILESEARCHPATH (R6 only)
	%S      Suffix.  None for app-defaults.  
	%L      Language, locale, and codeset (e.g. "ja_JP.EUC") 
	%l      Language part of %L (e.g. "ja") 
	%t      The territory part of the display's language string 
	%c      The codeset part of the display's language string

	Let's take apart the example.  Suppose the application's class name is
"Myterm". Also, suppose Open Windows is installed in /usr/openwin.
(Notice the example omits locale-specific lookup.)
	/usr/lib/X11/%T/%N        means /usr/lib/X11/app-defaults/Myterm
	$OPENWINHOME/lib/%T/%N    means /usr/openwin/lib/app-defaults/Myterm

	As the application initializes, Xt tries to open both of the above
app-defaults files, in the order shown.  As soon as it finds one, it reads it
and uses it, and stops looking for others.  The effect of this path is to
search first in /usr/lib/X11, then in /usr/openwin.

	Let's consider another example. This time, let's set
XUSERFILESEARCHPATH so it looks for the file Myterm.ad in the current working
directory, then for Myterm in the directory ~/app-defaults.
	setenv XUSERFILESEARCHPATH ./%N.ad:$HOME/app-defaults/%N

	The first path in the list expands to ./Myterm.ad.  The second expands
to $HOME/app-defaults/Myterm.  This is a convenient setting for debugging
because it follows the Imake convention of naming the app-defaults file
Myterm.ad in the application's source directory, so you can run the
application from the directory in which you are working and still have the
resources loaded properly.  NOTE: when looking for app-default files with
XUSERFILESEARCHPATH, for some bizarre reason, neither the type nor file suffix
is defined so %T and %S are useless.

	With R5 and R6, there's another twist.  You may specify a customization
resource value.  For example, you might run the "myterm" application like
this:
	myterm -xrm "*customization: -color"

	If one of your pathname specifications had the value
"/usr/lib/X11/%T/%N%C" then the expanded pathname would be
"/usr/lib/X11/app-defaults/Myterm-color" because the %C substitution character
takes on the value of the customization resource.

	The default XFILESEARCHPATH, compiled into Xt, is:
		/usr/lib/X11/%L/%T/%N%C:\  (R5) 
		/usr/lib/X11/%l/%T/%N%C:\  (R5)
		/usr/lib/X11/%T/%N%C:\     (R5) 
		/usr/lib/X11/%L/%T/%N:\
		/usr/lib/X11/%l/%T/%N:\ /usr/lib/X11/%T/%N

	(Note: some sites replace /usr/lib/X11 with a ProjectRoot in this
batch of default settings.)

	The default XUSERFILESEARCHPATH, also compiled into Xt, is
		<root>/%L/%N%C:\  (R5) 
		<root>/%l/%N%C:\  (R5)
		<root>/%N%C:\     (R5) 
		<root>/%L/%N:\ 
		<root>/%l/%N:\
		<root>/%N:

	<root> is either the value of XAPPLRESDIR or the user's home directory
if XAPPLRESDIR is not set.  If you set XUSERFILESEARCHPATH to some value other 
than the default, Xt ignores XAPPLRESDIR altogether.

	Notice that the quick and dirty way of making your application find
your app-defaults file in your current working directory is to set XAPPLRESDIR
to ".", a single dot.  In R3, all this machinery worked differently; for R3
compatibilty, many people set their XAPPLRESDIR value to "./", a dot followed
by a slash.

[Thanks to Oliver Jones (oj@world.std.com); 2/93.]

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Top Document: comp.windows.x Frequently Asked Questions (FAQ) 2/7
Previous Document: 38) Where are the resources loaded from?
Next Document: 40) How to I have xdm put a picture behind the log-in window?

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Last Update March 27 2014 @ 02:12 PM