get_rect.bash

#!/bin/bash -

get_rect() {
    local target
    target=$(bspc query -N -n "$1.floating") || return
    bspc subscribe node_geometry | while IFS=' ' read -r _ _ _ wid rect; do
        if (( wid == target )); then
            printf '%s\n' "$rect"
            break
        fi
    done &
    bspc node "$target" -z top 0 0
    wait %- 2> /dev/null
}

get_rect focused

posix_compliant_version.sh

#!/bin/sh -

get_rect() {
    target=$(bspc query -N -n "$1.floating") || return
    bspc subscribe node_geometry | while IFS=' ' read -r a b c wid rect; do
        if [ "$wid" = "$target" ]; then
            printf '%s\n' "$rect"
            break
        fi
    done &
    bspc node "$target" -z top 0 0
    wait %- 2> /dev/null
}

get_rect focused