logind-session-xorg-displays.sh

#!/usr/bin/env bash
set -euo pipefail
hash loginctl awk

log() { echo "[$(date --iso-8601=s)]  $*" >&2; }

if ! loginctl show-session &>/dev/null; then
    log "ERROR: no logind session found"
    exit 1
fi

{
    HEADER=("SESSION" "USERNAME" "XORG-DISPLAY")
    (IFS=$'\t'; echo "${HEADER[*]}")
    
    loginctl list-sessions |
        awk -v OFS=$'\t' \
            '$4 ~ /seat[0-9]+/ {
                display_cmd = "loginctl show-session --value -p Display "$1;
                display_cmd | getline xorg_display;
                print $1, $3, xorg_display;
                close(display_cmd);
             }'
} |
    column -t |
    {
        # print header to stderr
        sed -u '1q' >/dev/stderr
        # rest to stdout
        cat
    }