Desktop Entry Specification （桌面入口规范）
Version 1.5
Table of Contents
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.
Desktop entry files should have the .desktop extension, except for files of Type Directory which should have the .directory extension. Determining file type on basis of 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".
For applications, the part of the name of the desktop file before the .desktop extension should be a valid D-Bus well-known name. This means that it is a sequence of non-empty elements separated by dots (U+002E FULL STOP), none of which starts with a digit, and each of which contains only characters from the set [A-Za-z0-9-_]: ASCII letters, digits, dash (U+002D HYPHEN-MINUS) and underscore (U+005F LOW LINE).
The name of the desktop entry should follow the "reverse DNS" convention: it should start with a reversed DNS domain name controlled by the author of the application, in lower case. The domain name should be followed by the name of the application, which is conventionally written with words run together and initial capital letters (CamelCase). For example, if the owner of example.org writes "Foo Viewer", they might choose the name org.example.FooViewer, resulting in a file named org.example.FooViewer.desktop.
Well-known names containing the dash are allowed but not recommended, because the dash is not allowed in some related uses of reversed DNS names, such as D-Bus object paths and interface names, and Flatpak app IDs. If the author's domain name contains a dash, replacing it with an underscore is recommended: this cannot cause ambiguity, because underscores are not allowed in DNS domain names.
If the author's domain name contains a label starting with a digit, (which is not allowed in D-Bus well-known names), prepending an underscore to that element of the desktop entry name is recommended. For example, 7-zip.org might release an application named org._7_zip.Archiver.
Each desktop entry representing an application is identified by its desktop file ID, which is based on its filename.
To determine the ID of a desktop file, make its full path relative to the $XDG_DATA_DIRS component in which the desktop file is installed, remove the "applications/" prefix, and turn '/' into '-'.
For example /usr/share/applications/foo/bar.desktop has the desktop file ID foo-bar.desktop.
If multiple files have the same desktop file ID, the first one in the $XDG_DATA_DIRS precedence order is used.
For example, if $XDG_DATA_DIRS contains the default paths /usr/local/share:/usr/share, then /usr/local/share/applications/org.foo.bar.desktop and /usr/share/applications/org.foo.bar.desktop both have the same desktop file ID org.foo.bar.desktop, but only the first one will be used.
If both foo-bar.desktop and foo/bar.desktop exist, it is undefined which is selected.
If the desktop file is not installed in an applications subdirectory of one of the $XDG_DATA_DIRS components, it does not have an ID.
Desktop entry files are encoded in UTF-8. A file is interpreted as a series of lines that are separated by linefeed characters. Case is significant everywhere in the 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.
A group header with name groupname is a line in the format:
Group names may contain all ASCII characters except for [ and ] and control characters.
Multiple groups may not have the same name.
All {key,value} pairs following a group header until a new group header belong to the group.
The basic format of the desktop entry file requires that there be a group header named Desktop Entry. There may be other groups present in the file, 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 preceding this group in the desktop entry file but possibly one or more comments.
Entries in the file are {key,value} pairs in the format:
Space before and after the equals sign should be ignored; the = sign is the actual delimiter.
Only the characters A-Za-z0-9- may be used in key names.
As the case is significant, the keys Name and NAME are not equivalent.
Multiple keys in the same group may not have the same name. Keys in different groups may have the same name.
The value types recognized are string, localestring, iconstring, boolean, and numeric.
The escape sequences \s, \n, \t, \r, and \\ are supported for values of type string, localestring and iconstring, meaning ASCII space, newline, tab, carriage return, and backslash, respectively.
Some keys can have multiple values. In such a case, the value of the key is specified as a plural: for example, string(s). The multiple values should be separated by a semicolon and the value of the key may be optionally terminated by a semicolon. Trailing empty strings must always be terminated with a semicolon. Semicolons in these values need to be escaped using \;.
Keys with type localestring and iconstring may be postfixed by [*LOCALE*], where *LOCALE* is the locale type of the entry. *LOCALE* must be of the form *lang*_*COUNTRY*.*ENCODING*@*MODIFIER*, where _*COUNTRY*, .*ENCODING*, and @*MODIFIER* may be omitted. If a postfixed key occurs, the same key must be also present without the postfix.
When reading in the desktop entry file, the value of the key is selected by matching the current POSIX locale for the LC_MESSAGES category against the *LOCALE* postfixes of all occurrences of the key, with the .*ENCODING* part stripped.
The matching is done as follows. If LC_MESSAGES is of the form *lang*_*COUNTRY*.*ENCODING*@*MODIFIER*, then it will match a key of the form *lang*_*COUNTRY*@*MODIFIER*. If such a key does not exist, it will attempt to match *lang*_*COUNTRY* followed by *lang*@*MODIFIER*. Then, a match against *lang* by itself will be attempted. Finally, if no matching key is found the required key without a locale specified is used. The encoding from the LC_MESSAGES value is ignored when matching.
If LC_MESSAGES does not have a *MODIFIER* field, then no key with a modifier will be matched. Similarly, if LC_MESSAGES does not have a *COUNTRY* field, then no key with a country specified will be matched. If LC_MESSAGES just has a *lang* field, then it will do a straight match to a key with a similar value. The following table lists possible matches of various LC_MESSAGES values in the order in which they are matched. Note that the *ENCODING* field isn't shown.
Table 1. Locale Matching
For example, if the current value of the LC_MESSAGES category is sr_YU@Latn and the desktop file includes:
Name=Foo
Name[sr_YU]=...
Name[sr@Latn]=...
Name[sr]=...
then the value of the Name keyed by sr_YU is used.
Although icon names of type iconstring are localizable, they are not human-readable strings, so should typically not be handled by translation tools. Most applications are not expected to localize their icons; exceptions might include icons containing text or culture-specific symbology.
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.
Some keys only make sense in the context when another particular key is also present and set to a specific value. Those keys should not be used if the particular key is not present or not set to the specific value. For example, the Terminal key can only be used when the value of the Type key is Application.
If a REQUIRED key is only valid in the context of another key set to a specific value, then it has to be present only if the other key is set to the specific value. For example, the URL key has to be present when and only when when the value of the Type key is Link.
Some example keys: Name[C], Comment[it].
Table 2. Standard Keys
The Exec key must contain a command line. A command line consists of an executable program optionally followed by one or more arguments. The executable program can either be specified with its full path or with the name of the executable only. If no full path is provided the executable is looked up in the $PATH environment variable used by the desktop environment. The name or path of the executable program may not contain the equal sign ("="). Arguments are separated by a space.
Arguments may be quoted in whole. If an argument contains a reserved character the argument must be quoted. The rules for quoting of arguments is also applicable to the executable name or path of the executable program as provided.
Quoting must be done by enclosing the argument between double quotes and escaping the double quote character, backtick character (""), dollar sign ("$") and backslash character ("\") by preceding it with an additional backslash character. Implementations must undo quoting before expanding field codes and before passing the argument to the executable program. Reserved characters are space (" "), tab, newline, double quote, single quote ("'"), backslash character ("\"), greater-than sign (">"), less-than sign ("<"), tilde ("~"), vertical bar ("|"), ampersand ("&"), semicolon (";"), dollar sign ("$"), asterisk ("*"), question mark ("?"), hash mark ("#"), parenthesis ("(") and (")") and backtick character ("").
Note that the general escape rule for values of type string states that the backslash character can be escaped as ("\") as well and that this escape rule is applied before the quoting rule. As such, to unambiguously represent a literal backslash character in a quoted argument in a desktop entry file requires the use of four successive backslash characters ("\\"). Likewise, a literal dollar sign in a quoted argument in a desktop entry file is unambiguously represented with ("\$").
A number of special field codes have been defined which will be expanded by the file manager or program launcher when encountered in the command line. Field codes consist of the percentage character ("%") followed by an alpha character. Literal percentage characters must be escaped as %%. Deprecated field codes should be removed from the command line and ignored. Field codes are expanded only once, the string that is used to replace the field code should not be checked for field codes itself.
Command lines that contain a field code that is not listed in this specification are invalid and must not be processed, in particular implementations may not introduce support for field codes not listed in this specification. Extensions, if any, should be introduced by means of a new key.
Implementations must take care not to expand field codes into multiple arguments unless explicitly instructed by this specification. This means that name fields, filenames and other replacements that can contain spaces must be passed as a single argument to the executable program after expansion.
Although the Exec key is defined to have a value of the type string, which is limited to ASCII characters, field code expansion may introduce non-ASCII characters in arguments. Implementations must take care that all characters in arguments passed to the executable program are properly encoded according to the applicable locale setting.
Recognized field codes are as follows:
A command line may contain at most one %f, %u, %F or %U field code. If the application should not open any file the %f, %u, %F and %U field codes must be removed from the command line and ignored.
Field codes must not be used inside a quoted argument, the result of field code expansion inside a quoted argument is undefined. The %F and %U field codes may only be used as an argument on their own.
Applications that support being launched by D-Bus must implement the following interface (given in D-Bus introspection XML format):
<interface name='org.freedesktop.Application'>
<method name='Activate'>
<arg type='a{sv}' name='platform_data' direction='in'/>
</method>
<method name='Open'>
<arg type='as' name='uris' direction='in'/>
<arg type='a{sv}' name='platform_data' direction='in'/>
</method>
<method name='ActivateAction'>
<arg type='s' name='action_name' direction='in'/>
<arg type='av' name='parameter' direction='in'/>
<arg type='a{sv}' name='platform_data' direction='in'/>
</method>
</interface>
The application must name its desktop file in accordance with the naming recommendations in the introduction section (e.g. the filename must be like org.example.FooViewer.desktop). The application must have a D-Bus service activatable at the well-known name that is equal to the desktop file name with the .desktop portion removed (for our example, org.example.FooViewer). The above interface must be implemented at an object path determined as follows: starting with the well-known D-Bus name of the application, change all dots to slashes and prefix a slash. If a dash ('-') is found, convert it to an underscore ('_'). For our example, this is /org/example/FooViewer.
The Activate method is called when the application is started without files to open.
The Open method is called when the application is started with files. The array of strings is an array of URIs, in UTF-8.
The ActivateAction method is called when Desktop Actions are activated. The action-name parameter is the name of the action.
All methods take a platform-data argument that is used in a similar way to how environment variables might be used. Current fields described by the specification are:
The Implements key can be used to declare one or more interfaces that a desktop file implements.
Each interface name must follow the rules used for D-Bus interface names, but other than that, they have no particular meaning. For instance, listing an interface here does not necessarily mean that this application implements that D-Bus interface or even that such a D-Bus interface exists. It is entirely up to the entity who defined a particular interface to define what it means to implement it.
Although it is entirely up to the designer of the interface to decide what a given interface name means, here are some recommended "best practices":
- interfaces should require that application is DBusActivatable, including the requirement that the application's desktop file is named using the D-Bus "reverse DNS" convention
- the interface name should correspond to a D-Bus interface that the application exports on the same object path as it exports the org.freedesktop.Application interface
- if the interface wishes to allow for details about the implementation, it should do so by specifying that implementers add a group in their desktop file with the same name as the interface (eg: "[org.freedesktop.ImageAcquire]")
Recommendations notwithstanding, interfaces could specify almost any imaginable requirement including such (ridiculous) things as "when launched via the Exec line, the application is expected to present a window with the _FOO_IDENTIFIER property set, at which point an X client message will be sent to that window". Another example is "all implementations of this interface are expected to be marked NoDisplay and, on launch, will present no windows and will delete all of the user's files without confirmation".
Interface definers should take care to keep issues of backward and forward compatibility in mind when designing their interfaces.
Desktop entries of type Application can include one or more actions. An action represents an additional way to invoke the application. Application launchers should expose them to the user (for example, as a submenu) within the context of the application. This is used to build so called "Quicklists" or "Jumplists".
The following keys are supported within each action group. If a REQUIRED key is not present in an action group, then the implementor should ignore this action.
Table 3. Action Specific Keys
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*, e.g. 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-*PRODUCTGROUPNAME*] or something similar. These steps will avoid namespace clashes between different yet similar environments.
A. 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
Icon=fooview
MimeType=image/x-foo;
Actions=Gallery;Create;
[Desktop Action Gallery]
Exec=fooview --gallery
Name=Browse Gallery
[Desktop Action Create]
Exec=fooview --create-new
Name=Create a new Foo!
Icon=fooview-new
B. Currently reserved for use within KDE
For historical reasons KDE is using some KDE-specific extensions that are currently not prefixed by a X-KDE- prefix.
KDE also used the Keywords key before it was standardized, using commas instead of semi-colons as separators. At the time of standardization, the field had been prefixed with a X-KDE prefix, but the Trinity fork still used the non-prefixed variant.
KDE uses the following additional keys for desktop entries of the FSDevice type.
C. Deprecated Items
As this standard is quite old there are some deprecated items that may or may not be used by several implementations.
Type=MimeType is deprecated as there is a new standard for this now, see the Shared MIME-info Database specification for more information. In consequence the Keys Patterns (various file name extensions associated with the MIME type) and DefaultApp (the default application associated with this MIME type) are also deprecated.- Using
.kdelnk instead of .desktop as the file extension is deprecated.
- Using
[KDE Desktop Entry] instead of [Desktop Entry] as header is deprecated.
- The
Encoding key is deprecated. It was used to specify whether keys of type localestring were encoded in UTF-8 or in the specified locale. Possible values are UTF-8 and Legacy-Mixed. See Appendix D, The Legacy-Mixed Encoding (Deprecated) for more details.
- Deprecated
Exec field codes: %m (the mini-icon associated with the desktop entry, this should be expanded as two arguments, -miniicon and the content of the MiniIcon key, it can also be ignored by expanding it to no arguments), %v (the device as listed in the Dev key in the desktop file), %d (the directory of a file), %D (the directories of files), %n (the base name of a file) and %N (the base names of files).
- Deprecated keys:
MiniIcon (small icon for menus, etc.), TerminalOptions (if the program runs in a terminal, any options that should be passed to the terminal emulator before actually executing the program), Protocols, Extensions, BinaryPattern, MapNotify.
- The
SwallowTitle and SwallowExec keys are deprecated. The SwallowTitle key is of type localestring and specifies the title of the window if is swallowed onto the panel. The SwallowExec key is of type string and specifies the program to exec if swallowed app is clicked.
- The
SortOrder key is deprecated. It is of type string(s) and may be used to specify the order in which to display files. The Desktop Menu Specification defines another mechanism for defining the order of menu items.
- The
FilePattern key is deprecated. The value is a list of regular expressions to match against for a file manager to determine if this entry's icon should be displayed. Usually simply the name of the main executable and friends.
- Historically some booleans 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.
- Historically lists have been comma separated. 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.
D. The Legacy-Mixed Encoding (Deprecated)
The Legacy-Mixed encoding corresponds to the traditional encoding of desktop files in older versions of the GNOME and KDE desktop files. In this encoding, the encoding of each localestring key is determined by the locale tag for that key, if any, instead of being UTF-8. For keys without a locale tag, the value must contain only ASCII characters.
If the file specifies an unsupported encoding, the implementation should either ignore the file, or, if the user has requested a direct operation on the file (such as opening it for editing), display an appropriate error indication to the user.
In the absence of an Encoding key, the implementation may choose to autodetect the encoding of the file by using such factors as:
If the implementation does not perform such auto-detection, it should treat a file without an Encoding key in the same way as a file with an unsupported Encoding key.
If the locale tag includes an .*ENCODING* part, then that determines the encoding for the line. Otherwise, the encoding is determined by the language, or *lang*_*COUNTRY* pair from the locale tag, according to the following table.
The name given here is listed here is typically the canonical name for the encoding in the GNU C Library's iconv facility. Encodings marked with (*) are not currently supported by the GNU C Library; for this reason, implementations may choose to ignore lines in desktop files that resolve to this encoding. Desktop files with these encodings are currently rare or non-existent. Other names for the encoding found in existing desktop files. Language tags for which this is the default encoding.
This table above covers all tags and encodings that are known to be currently in use. Implementors may choose to support encodings not in the above set. For tags without defaults listed in the above table, desktop file creators must specify the .*ENCODING* part of the locale tag.
Matching the .*ENCODING* part of the locale tag against a locale name or alias should be done by stripping all punctuation characters from both the tag and the name or alias, converting both name and alias to lowercase, and comparing the result. This is necessary because, for example, Big5 is frequently found instead of BIG5 and georgianacademy instead of GEORGIAN-ACADEMY. Desktop files creators should, however, use the name as it appears in the "Encoding" column above.
E. Changes to this Specification
Add DBusActivatable key.
Add support for Actions.
Add Keyword key.
Make Exec key mandatory.
Make Version key a string.
Make UnmountIcon key a localestring.
转载自：https://specifications.freedesktop.org/desktop-entry-spec/latest/