In the
X Window System
The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems.
X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wit ...
, the X resources are
parameter
A parameter (), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when ...
s of
computer program
A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components.
A computer program ...
s such as the name of the
font
In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design.
In mod ...
used in the
button
A button is a fastener that joins two pieces of fabric together by slipping through a loop or by sliding through a buttonhole.
In modern clothing and fashion design, buttons are commonly made of plastic but also may be made of metal, wood, ...
s, the
background color of
menu
In a restaurant, the menu is a list of food and beverages offered to customers and the prices. A menu may be à la carte – which presents a list of options from which customers choose – or table d'hôte, in which case a pre-established seque ...
s, etc. They are used in conjunction with or as an alternative to
command line
A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
parameters and
configuration file
In computing, configuration files (commonly known simply as config files) are computer file, files used to configure the Parameter (computer programming), parameters and Initialization (programming), initial settings for some computer programs. T ...
s.
Format
At the X protocol level, resources are strings that are stored in the server and have no special meaning. The syntax and meaning of these strings is given by client libraries and applications.
Every X resource specifies a parameter for a program or one of its components. A fully specified resource has the following format:
:
application.component.subcomponent.subcomponent.attribute: value
This resource specifies the value of
attribute
for the component named
component.subcomponent.subcomponent
of the program
application
. Resources are often used for specifying the parameters of
widgets created by the application. Since these widgets are arranged in a
tree
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
, the sequence of component/subcomponent names is used to identify a widget by giving its path within the tree. The value of the resource is the value of an attribute for this widget, such as its background color, etc.
X resources are also used to specify parameters for the program that are not directly related to its widgets, using the same syntax.
X resources are designed to allow the same parameter to be specified for more than one program or component. This is realized by allowing
wildcard character
In software, a wildcard character is a kind of placeholder represented by a single character, such as an asterisk (), which can be interpreted as a number of literal characters or an empty string. It is often used in file searches so the full na ...
s in a resource specification. In particular, the
? character is used to match the application name or a single component. The
* character is used to match any number of components. These two characters can be used anywhere but at the end of the resource name. In other words, an attribute cannot be replaced by a wildcard character.
While the resources can be loosely specified via the wildcard characters, queries for the value of a resource must specify that resource exactly. For example, a resource can specify that the background of every component of the
xmail
program must be red:
:
xmail*background: red
However, when a program (e.g., the
xmail program itself, when it wants to find out which background color to use) accesses the resource database via
Xlib
Xlib (also known as libX11) is an X Window System protocol client library written in the C programming language. It contains functions for interacting with an X server. These functions allow programmers to write programs without knowing the ...
functions, it can only request the value of a specific resource. Contrary to most
database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...
s, the stored data can be specified loosely (via wildcard characters), but the interrogation cannot. For example, a program can query for the value of
xmail.main.background
or of
xmail.toc.buttons.background
, but cannot use
?
or
*
to check the background color of several components at once.
Resources can also be specified for ''classes'' of elements: for example,
application.widget.widget.attribute: value
can be generalized by replacing the application name with its class (e.g.,
Mail
instead of
xmh
), each widget with its type (
Pane
,
Button
, etc.), and the attribute with its type.
Location and use
During X
display server
In computing, a windowing system (or window system) is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the WIMP (windows, icons, menus, pointer) paradigm for ...
execution, the X resources are stored in two standard locations, depending on whether they apply to all screens or to a particular one:
# the
RESOURCE_MANAGER
property of the root window of screen 0
# the
SCREEN_RESOURCES
property of the root window of an arbitrary screen
X resources are stored in the server rather than in a configuration file to allow programs started from other computers to use them. Indeed, a program connecting to an X display server from another computer can access the resources via the
X protocol. Using the old system of storing program parameters in the
.Xdefaults
file creates the need of copying this file to all other computers where a program can be started.
Resources are manipulated by the
xrdb program. In particular, many X display server configurations run xrdb at start up, instructing it to read the resources from the
.Xresources
file in the user's
home directory
A home directory is a file system directory on a multi-user operating system containing files for a given user of the system. The specifics of the home directory (such as its name and location) are defined by the operating system involved; for ...
. From this point on, every other program finds the resources in the two standard locations.
You can view the current resources from a console with
xrdb -query
.
Client libraries
Xlib
Xlib (also known as libX11) is an X Window System protocol client library written in the C programming language. It contains functions for interacting with an X server. These functions allow programmers to write programs without knowing the ...
contains a number of
convenience functions for accessing the resources on the server and manipulating them locally. These functions are used both by xrdb and by every other program that needs these resources. Most of these functions manipulate a ''resource database'', which is a local data structure representing a set of resource specifications. The Xlib functions for resource management are:
* functions for reading the resources on the server into a local string (
XResourceManagerString
and
XScreenResourceString
)
* functions for creating, manipulating, and destroying a local resource database (
XrmInitialize
,
XrmDestroyDatabase
,
XrmGetFileDatabase
,
XrmPutFileDatabase
,
XrmGetStringDatabase
,
XrmLocaleOfDatabase
,
XrmSetDatabase
,
XrmGetDatabase
,
XrmCombineFileDatabase
,
XrmCombineDatabase
,
XrmMergeDatabases
,
XrmParseCommand
)
* functions for looking up resources and storing new ones (
XrmGetResource
,
XrmQGetResource
,
XrmQGetSearchList
,
XrmQGetSearchResource
,
XrmPutResource
,
XrmQPutResource
,
XrmPutStringResource
,
XrmQPutStringResource
,
XrmPutLineResource
,
XrmEnumerateDatabase
)
In particular, the function
XrmParseCommand
allow parsing the
command line
A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
arguments, reading resources that are then added to a local resource database. This way, the resources can be read from the server and used as defaults that are overridden by command line arguments.
For the sake of efficiency, integers called ''quarks'' are defined to represent local strings. Quarks are similar to
atoms
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, an ...
, but they represent strings stored locally rather than on the server. A number of Xlib functions create an association between strings and quarks. Quarks can be used in place of component names when using one of the above functions; resource names therefore correspond to quark lists.
See also
*
X Window System protocols and architecture
In computing, the X Window System (commonly: X11, or X) is a network-transparent windowing system for bitmap displays. This article details the protocols and technical structure of X11.
Client–server model and network transparency
X uses a ...
References
{{Reflist
External links
Inessential X Resources for Techno-DweebsResource Manager Functionsof the
Xlib
Xlib (also known as libX11) is an X Window System protocol client library written in the C programming language. It contains functions for interacting with an X server. These functions allow programmers to write programs without knowing the ...
client library
X Window System