Can Opener is a programmable URL handler for Mac OS X. If you often find yourself switching back and forth between Safari and Chrome, for example, you can program Can Opener to open the URL in whichever browser is currently running at the moment. Or, if use Safari most of the time, but have a few websites you want to always open in Chrome, you can program Can Opener to do that, too.
I say "program" because at the heart of Can Opener is a script that you write. Every time Can Opener is asked to open a URL, it runs your script, and does what the script tells it to do.
Can Opener is free software. It is licensed under the GNU General Public License, which protects your freedoms as a user of the software.
For example, you can inspect the source code to verify that it doesn't track which websites you visit and transmit that information without your consent.
You can write your URL opening script in whatever language you choose: Ruby, Python, Bash, C, C++, PHP, etc. As long as the script can read environment variables and write to standard output, it is supported.
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The URL to be opened is passed in as the first command line argument, and also in the environment with the name
URL. -
If any applications are installed which claim to handle URLs of that scheme, their bundle identifiers are provided as a colon-separated list in the environment variable
AVAILABLE_APPS. -
The subset of those apps that are running are provided in the environment variable
RUNNING_APPS, in the same format.
The script communicates back to Can Opener by printing to standard output.
If the script prints Use:, followed by a space, followed by a bundle
identifier, then the corresponding app will be used to open the URL.
For example, for Safari:
Use: com.apple.Safari
If the script prints multiple Use: lines, then the user will be prompted to
choose from the options. For example, to give the option of Safari or Chrome:
Use: com.apple.Safari
Use: com.google.Chrome
The script must print at least one Use: line.
Optionally, the script can choose a different URL to open by printing URL:,
followed by a space, followed by the new URL. This is useful, for example, if
you want to redirect feed: URLs to a web app like NewsBlur.
Can Opener has built in support for Ruby. If you require 'can_opener' at the
top of your script, you can write code like Safari.running?.
Make an icon.
Keyboard control of the browser chooser window: right-left arrows to choose a button, return to open, escape to close window.
Store the contents of the script file, and not just the path, in NSUserDefaults. Or make the script file a fixed location (for example, in the user's Library folder). Either way, it doesn't make a lot of sense to have the script location be configurable; it just makes getting started more difficult.
Can Opener's preferences window should include a script editor.
It should use a default script that chooses from running browsers. This would make Can Opener more useful "out of the box".
The Chooser Window could be a whole lot more slick looking.
This should probably be one of those little no-icon, menu-bar-only apps.
Protect against infinite loops, if a script is dumb enough to invoke CanOpener
to open the same URL it is opening. (Could easily happen if CanOpener is the
default handler and the script simply calls open $URL.)
URL schemes must be declared in the Info.plist file; that is, they can't be changed without hacking the app.
See the source code for more TODO comments.
Choosy: a smarter default browser. Choosy is very similar to Can Opener, but it is proprietary and non-free. At the time I began working on Can Opener (October 2015) it also hadn't been updated in several years.
Since then, version 1.1 was released in January 2016, so if you are looking for something similar to Can Opener but easier-to-use, check it out.
Bwana: A man page reader for your browser. The source code was a useful reference for handling GetURL Apple Events.
Make Your Own URL Protocol and Handler. A similar idea, in AppleScript.