デフォルトアプリケーション

Programs implement default application associations in different ways. While command-line programs traditionally use environment variables, graphical applications tend to use XDG MIME Applications through either the GIO API, the Qt API, or by executing /usr/bin/xdg-open, which is part of xdg-utils. Because xdg-open and XDG MIME Applications are quite complex, various alternative resource openers were developed. The following table lists example applications for each method.

Method	Uses XDG	Application examples
GIO's GAppInfo	Yes	Firefox, GNOME Files, PCManFM, Thunar, Thunderbird, Telegram
/usr/bin/xdg-open	By default	Chromium (Open downloaded file)
custom	Usually not	mc, ranger
environment variables	No	man, sudoedit, systemctl
D-Bus's FileManager1	org.freedesktop.FileManager1	Firefox (Open containing folder), Zotero (Show file), Telegram (Show in folder)

Many desktop environments and graphical file managers provide a GUI for configuring default applications.

Background information

Programs sometimes need to open a file or a URI in the user's preferred application. To open a file in the user's preferred application the filetype needs to be detected (usually using filename extensions or magic numbers mapped to MIME types) and there needs to be an application associated with the filetype.

Heirloom UNIX programs used mime.types for MIME type detection and mailcap for application association.

Resource openers

• XDG MIME Apps: implements the XDG MIME Applications specification
• RegEx rules: allows MIME types to be associated with applications using regular expressions
• URI support: allows arbitrary URI schemes to be associated with applications

Name	Package	XDG MIME Apps	RegEx rules	URI support
xdg-open	xdg-utils	Yes	No	Yes
mimeopen(1p)	perl-file-mimeinfo	Yes	No	No
mimeo	mimeoAUR	Yes	Yes	Yes
whippet	whippetAUR	Yes	No	Yes
linopen	linopenAUR	No	Yes	Yes
mimi	mimi-gitAUR	No	No	partly
busking	busking-gitAUR	No	Yes	Yes
sx-open	sx-openAUR	No	Yes	Yes
rifle(1)	ranger	No	Yes	No
handlr	handlr-binAUR	Yes	No	Yes

xdg-open

xdg-open (part of xdg-utils) implements XDG MIME Applications and is used by many programs.

Because of the complexity of the xdg-utils version of xdg-open, it can be difficult to debug when the wrong default application is being opened. Because of this, there are many alternatives that attempt to improve upon it. Several of these alternatives replace the /usr/bin/xdg-open executable, thus changing the default application behavior of most applications. Others simply provide an alternative method of choosing default applications.

perl-file-mimeinfo

perl-file-mimeinfo provides the tools mimeopen(1p) and mimetype(1p). These have a slightly nicer interface than their xdg-utils equivalents:

# determine a file's MIME type
$ mimetype photo.jpeg
photo.jpeg: image/jpeg

# choose the default application for this file
$ mimeopen -d photo.jpeg
Please choose an application

    1) Feh (feh)
    2) GNU Image Manipulation Program (gimp)
    3) Pinta (pinta)

use application #

# open a file with its default application
$ mimeopen -n photo.jpeg

Most importantly, xdg-utils programs will actually call file instead of mimetype for MIME type detection if it does not detect your desktop environment. This is important because file does not follow the XDG standard.

ノート: perl-file-mimeinfo before 0.28-1 did not entirely follow the XDG standard. For example it did not not read distribution-wide defaults and it saved its config in deprecated locations.

mimeo

mimeo^AUR provides the tool mimeo, which unifies the functionality of xdg-open and xdg-mime.

# determine a file's MIME type
$ mimeo -m photo.jpeg
photo.jpeg
  image/jpeg

# choose the default application for this MIME type
$ mimeo --add image/jpeg feh.desktop

# open a file with its default application
$ mimeo photo.jpeg

However a big difference with xdg-utils is that mimeo also supports custom "association files" that allow for more complex associations. For example, passing specific command line arguments based on a regular expression match:

# open youtube links in VLC without opening a new instance
vlc --one-instance --playlist-enqueue %U
  ^https?://(www.)?youtube.com/watch\?.*v=

xdg-utils-mimeo^AUR patches xdg-utils so that xdg-open falls back to mimeo if no desktop environment is detected.

whippet

whippet^AUR provides the tool whippet, which is similar to xdg-open. It has X11 integration by using libnotify to display errors and dmenu to display choices between applications to open.

# open a file with its default application
$ whippet -M photo.jpeg

# choose from all possible applications for opening a file (without setting a default)
$ whippet -m photo.jpeg

In addition to implementing XDG MIME Applications, whippet can also use a SQlite database of weighted application/MIME type/regex associations to determine which app to use.

handlr

handlr-bin^AUR, written in Rust, provides the functionality of xdg-open and xdg-mime with a streamlined interface.

Compared to xdg-utils, it includes:

• setting associations by extension, removing the need to look up or remember mime types
• validation for mime types and extensions
• removal of invalid entries from mimeapps.list
• intelligent detection of mime types from file content in case filename is ambiguous
• autocompletion of mimes, extensions, and desktop entries

# The following two are identical
handlr set .png feh.desktop
handlr set image/png feh.desktop

# List default apps
handlr list

# Get the handler for a mime/extension
$ handlr get .png --json
{"handler":"pqiv.desktop","name":"pqiv","cmd":"/usr/bin/pqiv"}

# Launch a handler with optional path/URL
handlr launch x-scheme-handler/https
handlr launch x-scheme-handler/https -- https://google.ca

xdg-utils-handlr^AUR provides an xdg-open that uses handlr under the hood to replace xdg-utils.

Minimalist replacements

The following packages conflict with and provide xdg-utils because they provide their own /usr/bin/xdg-open script.

If you want to use one of these resource openers while still being able to use xdg-utils, install them manually in a PATH directory before /usr/bin.

• linopen^AUR - 170-line Bash script, supports regex rules
• mimi-git^AUR - 130-line Bash script, can change command arguments for each MIME type
• busking-git^AUR - 80-line Perl script similar to mimi but also supports regex rules
• sx-open^AUR - 60-line Bash script, uses a simple shell-based config file

run-mailcap

警告: If you use run-mailcap^AUR, it is possible for xdg-open to delegate to it. This will cause an infinite loop if you are using the /etc/mailcap from mailcap, because it also delegates to xdg-open.