Let the (terminal) bells ring out

2023Q4. Last update Dec 2023. History↓

I just wanted to take a few minutes to argue that the venerable terminal bell is a helpful and perhaps overlooked tool for anyone who does a lot of their work out of a terminal window. First, an important clarification. Bells ringing, chiming, or (as is appropriate for the season) jingling all sounds very noisy - but although you can configure your terminal emulator to emit a sound for the terminal bell, I'm actually advocating for configuring a non-intrusive but persistent visual notification.

BEL

Our goal is to generate a visual indicator on demand (e.g. when a long-running task has finished) and to do so with minimal fuss. This should work over ssh and without worrying about forwarding connections to some notification daemon. The ASCII BEL control character (alternatively written as BELL by those willing to spend characters extravagantly) meets these requirements. You'll just need co-operation from your terminal emulator and window manager to convert the bell to an appropriate notification.

BEL is 7 in ASCII, but can be printed using \a in printf (including the /usr/bin/printf you likely use from your shell, defined in POSIX). There's even a Rosetta Code page on ringing the terminal bell from various languages. Personally, I like to define a shell alias such as:

alias bell="printf '\aBELL!\n'"

Printing some text alongside the bell is helpful for confirming the bell was triggered as expected even after it was dismissed. Then, if kicking off a long operation like an LLVM compile and test use something like:

cmake --build . && ./bin/llvm-lit -s test; bell

The ; ensures the bell is produced regardless of the exit code of the previous commands. All being well, this sets the urgent hint on the X11 window used by your terminal, and your window manager produces a subtle but persistent visual indicator that is dismissed after you next give focus to the source of the bell. Here's how it looks for me in DWM:

Screenshot of DWM showing a notification from abell

The above example shows 9 workspaces (some of them named), where the llvm workspace has been highlighted because a bell was produced there. You'll also spot that I have a timers workspace, which I tend to use for miscellaneous timers. e.g. a reminder before a meeting is due to start, or when I'm planning to switch a task. I have a small tool for this I might share in a future post.

A limitation versus triggering freedesktop.org Desktop Notifications is that there's no payload / associated message. For me this isn't a big deal, such messages are distracting, and it's easy enough to see the full context when switching workspaces. It's possible it's a problem for your preferred workflow of course.

You could put \a in your terminal prompt ($PS1), meaning a bell is triggered after every command finishes. For me this would lead to too many notifications for commands I didn't want to carefully monitor the output for, but your mileage may vary. After publishing this article, my Igalia colleague Adrian Perez pointed me to a slight variant on this that he uses: in Zsh $TTYIDLE makes it easy to configure behaviour based on the duration of a command and he configures zsh so a bell is produced for commands that take longer than 30 seconds to complete.

Terminal emulator support

Unfortunately, setting the urgent hint upon a bell is not supported by gnome-terminal, with a 15 year-old issue left unresolved. It is however supported by the otherwise very similar xfce4-terminal (just enable the visual bell in preferences), and I switched solely due to this issue.

From what I can tell, this is the status of visual bell support via setting the X11 urgent hint:

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