Working with Polybar in EXWM: Part 1

2022-07-15 by Bryan Paronto

I've been daily driving the Emacs X Window Manager as my main window manager for the past 6 months at this point, and for me, it's been a great tool. It's not without some quirks, but on the whole it's enabled me from move from using a disparate set of tools to now having an Integrated Computing Environment, from within which I can manage my GTD workflow, blog, read Emails & RSS Feeds, browse the web and more. It's true: Emacs really does make a great Operating System.

Starting and Stopping Polybar

The Problem

Like many recent converts, I adopted a lot of the configuration used by David Wilson of System Crafters. Part of that configuration as his efs/start-panel & efs/kill-panel functions. These functions start a polybar shell command from within emacs, being sure to kill any existing processes before spawn a new instance of the bar. It does this by capturing a reference to the process to that later it can be passed to the built-in kill-process function.

Unfortunately, I run a multi-monitor setup and David's script I borrowed, only launches polybar on the main screen. As a temporary workaround, I continued to use the bash script I call from within my old bspwm configuration to launch polybar. This didn't feel very Emacs Zen-like, so I set out to devise a better way.

My Solution

I came up with the following:

First, I set up an empty variable which will later fold references to the running polybar instances.

(defvar bp/polybar-processes nil
  "A list of running polybar processes. So that we can kill them later. 👿")

In the next section, I query for a list of attached monitors, this type via polybar itself. I could use xrandr for this, but this output is easier to parse, and it's one less dependency to rely upon from within a single script. Using cut I split the input by the delimiter ":", and take the first fragment, remove extraneous new-lines, and finally break the monitor names onto their own entries

(defun bp/get-monitors-list ()
  "Get a list of the currently connected monitors.

Requires polybar, instead of relying on xrandr,
 though you probably want it installed too."
   (substring (shell-command-to-string "polybar -m | cut -d: -f 1") 0 -1) "\n"))

As defined, the bp/kill-panel function will iterate over the list of running polybar processes and terminate them in succession, and finally, resetting the process list to nil.

(defun bp/kill-panel ()
  "Stop any running polybar processes"
  (let ((process-list bp/polybar-processes))
    (dolist (p process-list)
     (kill-process p)))
  (setq bp/polybar-processes nil))

As it's first order of business, the bp/start-panel function calls the bp/kill-panel function to clear out any existing running processes. It then calls bp/get-monitors-list, mapping over our list monitors and interpolating their names into the shell command to start polybar.

(defvar bp/polybar-config-location "~/.doom.d/exwm/polybar.config.ini"
  "The customized location of your polybar config.ini.
 You'll most certainly want to customize this value. ")

(defun bp/start-panel ()
  "Start polybar on each connected monitor"
  (setq bp/polybar-processes
        (mapcar (lambda (monitor)
                  (start-process-shell-command "polybar" nil
                                               (format "MONITOR=%s polybar -c %s --reload main" monitor bp/polybar-config-location)))

With these in place, I can now interactively show and hide the polybar as needed from within Emacs.

Bryan Paronto is a software engineer and all around technology nerd living in Chicago with his girlfriend and their 3 cats. He can be found here blogging or over on Twitch talking to himself while he codes.