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List:       kde-devel
Subject:    Desktop Entry Standard - Take 2
From:       <pbrown () redhat ! com>
Date:       1999-05-04 20:30:12
[Download RAW message or body]

Here's the next iteration of the Desktop Entry Standard:

-------
Desktop Entry Standard
Version 0.8.5
May 03, 1999

Preston Brown <pbrown@kde.org>
Jonathan Blandford <jrb@redhat.com>
Owen Taylor <otaylor@gtk.org>

Abstract
--------

Both the KDE and GNOME desktop environments have adopted a similar
format for "desktop entries," or configuration files describing how a
particular program is to be launched, how it appears in menus, etc.
It is to the larger community's benefit that a unified standard be
agreed upon by all parties such that interoperation between the two
environments, and indeed any additional environments that implement
the specification, becomes simpler.

1. Basic format of the file
---------------------------

Thes desktop entry files should have an extension of ".desktop" or
".kdelnk".  ".kdelnk" is deprecated, and is only maintained for
backwards compatibility.  Determining file type on basis fo extension
makes determining the file type very easy and quick.  When no file
extension is present, the desktop system should fall back to
recognition via "magic detection."  Desktop entries which describe how
a directory is to be formatted/displayed should be simply called
".directory".

The basic format of the desktop entry file requires that there be a
"group" header named "[Desktop Entry]".  For backwards compatibility,
implementations may also support the header "[KDE Desktop Entry]".
This "group" entry denotes that all {key,value} pairs following it
belong in the Desktop Entry group.  There may be other groups present
in the file (see MIME types discussion below), but this is the most
important group which explicitly needs to be supported.  This group
should also be used as the "magic key" for automatic mime type
detection.  There should be nothing proceeding this group in the
desktop entry file but possibly one or more comments (see below).

Lines beginning with a "#" are considered comments and will be
ignored, however they should be preserved across reads / writes of the 
desktop entry file.

Compliant implementations MUST not remove any fields from the file,
even if they don't support them.  Such fields must be maintained in a
list somewhere, and if the file is "rewritten," they will be included.
This ensures that any desktop-specific extensions will be preserved
even if another system accesses and changes the file.

Entries in the file are {key,value} pairs in the format:

Name=Value

Space before and after the equals sign should be supported; the "="
sign is the actual delimiter.

2. Possible value types
-----------------------

The value types recognized are string, unicode string, boolean
(encoded as the string true/false), and numeric.  Strings may have
locale-specific characters included, which should be identified as
part of the key, as described below.

Some keys can have multiple values; these should be separated by a
semicolon.  Those keys which have several values should have a
semicolon as the trailing character.

3. Recognized desktop entry keys
--------------------------------

Keys may be postfixed by [val], where val is the LOCALE type of the
string or numeric entry.  The locale entries should match those of the
standard C library.  Locales which specify a specify a specific
country should fall back to just the language name if no entry is
available, i.e if the locale is set to pt_BR, and a key with [pt] is
available, it should be used.  When no [language] postfix is present,
the C locale [C] is assumed.

Case is significant.  The keys "Name" and "NAME" are not equivalent.
The same holds for group names.  Key values are case sensitive as
well.

Keys are either OPTIONAL or REQUIRED.  If a key is optional it may or
may not be present in the file.  However, if it isn't, the
implementation of the standard should not blow up, it must provide
some sane defaults.  Additionally, keys either MUST or MAY be
supported by a particular implementation.

Some keys only make sense in the context when another particular key
is also present.

Some example keys: Name[C], Comment[it].

The following table is 100 columns wide.

Key		Description					Value Type	REQ?	MUST?
-------------------------------------------------------------------------------------------------
Version		version of Desktop Entry Specification		numeric (4)	NO	YES
Name		name of the entry, need not match binary name	string		YES	YES
Type		the type of desktop entry			string (1)	YES	YES
TryExec		name of physical binary on disk.  Can be used	string		NO	NO
		to a) determine if the binary is actually
		present, and not display in menus if it isn't,
		and b) associate the desktop entry's icon with
		a physical binary.  Replaces BinaryPattern.
NoDisplay	whether not to display in menus, etc.		boolean		NO	NO
Comment		descriptive comment				string		NO	YES
Exec		program to execute, possibly with arguments	string		NO	YES
Actions		additional actions possible, see MIME type	string(s)	NO	YES
		discussion in section 5
Icon		icon to display in file manager, menus, etc.	string		NO	YES
		the icon MAY specify a specific path to
		override common search directories
MiniIcon	small icon for window manager, menus, etc.	string		NO	NO
Path		if entry is type Application, the working	string		NO	YES
		directory to run the program in	
Terminal	whether the program runs in a terminal window	boolean (2)	NO	YES
TerminalOptions	if the program runs in a terminal, any options	string		NO	NO
		that should be passed to the terminal emulator
		before actually executing the program
SwallowTitle	if entry is swallowed onto the panel, this	string		NO	NO
		should be the title of window
SwallowExec	program to exec if swallowed app is clicked	string		NO	NO


MimeType	the MIME type(s) supported by this entry	string(s)
Patterns	if entry is type MimeType, various file name
		extensions associated with the MIME type.	string(s)	NO	NO
DefaultApp	if entry is type MimeType, the default
		application associated with this mime type	string		NO	NO


Dev		if FSDevice type of entry, the device to mount	string		NO	NO
FSType		The type of filesystem to try to mount		string		NO	NO
MountPoint	if FSDevice type of entry, the mount point	string		NO	NO
		of the device in question
ReadOnly	if FSDevice type of entry, specifies whether	boolean (2)	NO	NO
		or not the device is read-only
UnmountIcon	icon to display when device is not mounted	string		NO	NO
		Mounted devices display icon from Icon key


SortOrder	if entry of type Directory, this may specify	strings (3)	NO	NO
		the order in which to display files


URL		if entry is Link type, the URL to access	string		NO	YES

-------------------------------------------------------------------------------------------------

Notes:

(1) possible values are Application, Link, FSDevice, MimeType, Directory 

(2) historically these have been represented by the numeric entries 0
    or 1.  With this version of the standard they are now to be
    represented as a boolean string.  However, if an implementation is
    reading a pre-1.0 desktop entry, it should interpret 0 and 1 as false
    and true, respectively.  

(3) historically this has been a comma separated list.  This is inconsistent
    with other lists which are separated by a semicolon.  When reading
    a pre-1.0 desktop entry, comma separated lists should continue to
    be supported.

(4) while the version field is not required to be present, it should
    be in all newer implementations of the Desktop Entry specification.
    If the version number is not present, a "pre-standard" desktop entry
    file is to be assumed.


4. List of valid Exec parameter variables
-----------------------------------------

Each "Exec" field may take a number of arguments which will be
expanded by the file manager or program launcher and passed to the
program if necessary.  Recognized fields are as follows:

%f - a list of files.  If files are not on the local file system
     (i.e. HTTP or FTP locations), the files will be copied to the local
     file system and %f will be expanded to point at the temporary
     file.  Used for programs that do not understand URL syntax.

%F - a single file name, even if multiple files are selected.
     Implementations should probably spawn and execute multiple copies 
     of a program for each selected file if the program is not able to
     handle multiple file arguments.

%u - a list of URLs.

%d - the working directory.

%i - the icon associated with the desktop entry

%m - the mini-icon associated with the desktop entry

%c - the comment associated with the desktop entry

%s - this is currently supported by KDE, but we are not sure what it
     does.  Please fill this in.


5. Detailed discussion of supporting MIME types

It is in every desktop's best interest to have thorough support for
mime types.  The old /etc/mailcap and /etc/mime.types files are rather
limited in scope and frankly, are outdated.  Various desktop systems
have come up with different ways of extending this original system,
but none are compatible with each other.  The Desktop Entry Standard
hopes to be able to provide the beginnings of a solution to this
problem.

At a very basic level, the "Exec" key provides the default action to
take when the program described by a desktop entry is used to open a
document or data file.  Usually this consists of some action along the
lines of "kedit %f" or "ee %f".  This is a good
start, but it isn't as flexible as it can be.

Let us first establish that a program which supports a MIME type or
multiple mime types may be able to support multiple actions on those
MIME types as well.  The desktop entry may want to define additional
actions in addition to the default.  The toplevel "Exec" key describes
the default action; Let us define this action to also be known as the
"Open" action.  Additional actions which might be possible include
View, Edit, Play, etc.  A further revision of this document will
probably specify several "standard" actions in addition to the default
"Open" action, but in all cases, the number of actions is arbitrary.

Let us use a sound player as a simple example.  Call it sp.  The
default Exec (Open) action for this program would likely look
something like:

Exec=sp %u

However, imaging the sound player also supports editing of sound files
in a graphical manner.  We might wish to define an additional action
which could accomodate this.  Adding the action would be performed
like this:

Actions=Edit;

[Desktop Action Edit]
Exec=sp -edit %u

As you can see, defining the action "edit" will enable an additional
group of the name [Desktop Action <actionname>] to be read.  This
group can contain an additional Exec line, as well as possibly other
information like a new Name, Comment, Icon, and Path.  Thus
right-clicking on a .wav file will show both the default "Open" action
and this "Edit" action to both be displayed as choices in the
context-menu.  A left click (double or single, whichever the file
manager implements) would cause the default action to take place.
These are implementation-specific details which are up to the
implementer, and are not enforced by this standard.

If no DefaultApp is specified for a particular MIME type, any one of
the programs registered which claim to be able to handle the MIME type
may become the default handler.  This behaviour is undefined and
implementation-specific.


5. Extending the format
-----------------------

If the standard is to be amended with a new {key,value} pair which
should be applicable to all supporting parties, a group discussion
will take place.  This is the preferred method for introducing
changes.  If one particular party wishes to add a field for personal
use, they should prefix the key with the string "X-PRODUCT",
i.e. "X-NewDesktop-Foo", following the precedent set by other IETF and RFC
standards.

Alternatively, fields can be placed in their own group, where they may
then have arbitrary key names.  If this is the case, the group should
follow the scheme outlined above, i.e. [X-PRODUCT GROUPNAME] or
something similar.  These steps will avoid namespace clashes between
different yet similar environments.


6. Example Desktop Entry File
-----------------------------

[Desktop Entry]
Version=1.0
Type=Application
Name=Foo Viewer
Comment=The best viewer for Foo objects available!
TryExec=fooview
Exec=fooview %F
Actions=Edit;Inverse
Icon=fooview.png
MimeType=image/x-foo

[Desktop Action Inverse]
Exec=fooview --inverse %f
Name=Foo Viewer (inverse image)

[Desktop Action Edit]
Exec=fooview --edit %f
Name=Foo Viewer (edit image)
Icon=fooview-edit.png

------

---
  Preston Brown                                    Systems Engineer
  pbrown@redhat.com                                Red Hat Software, Inc. 

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