Tracks the previosly focused window in sway and marks it with '_prev'

track_prev_focus

#!/bin/sh

prev_focus=$(swaymsg -r -t get_seats | jq '.[0].focus')

swaymsg -m -t subscribe '["window"]' | \
  jq --unbuffered 'select(.change == "focus").container.id' | \
  while read new_focus; do
    swaymsg "[con_id=${prev_focus}] mark --add _prev" &>/dev/null
    prev_focus=$new_focus
  done

Referenced in this reddit: https://www.reddit.com/r/swaywm/comments/etpjix/i_created_a_script_to_implement_window_back_and/?utm_source=share&utm_medium=web2x&context=3

You can find a somewhat expanded version (incl. i3 support) here