Discover DBus Session and Display for a User

dbus-session-discovery.md

Discover a DBUS Session Deterministically

A set of Bash functions and a main method:

#!/usr/bin/env bash

function .dbus-session-pid() {
  # get all procs by this user which are running dbus-daemon that have --session in the flags
  ps aux | awk -v u=$USER -v b=/usr/bin/dbus-daemon '$1 == u && $11 == b {print $0;}' | \
    grep -P '\s+--session\b' | awk '{print $2;}'
}

function .dbus-pid-to-display() {
  local dbus_session_pid=$1
  grep -z DISPLAY /proc/$dbus_session_pid/environ | awk -F = '{print $2;}'
}

function main() {
  local args=("$@")
  
  local dbus_pid="$(.dbus-session-pid)"
  local display="$(.dbus-pid-to-display $dbus_pid)"
  
  echo "$USER: DBus Session Process Id $dbus_pid, DISPLAY=$display"
}

if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
  set -e
  main "$@"
fi

An example invocation yields the following for me:

naftuli: DBus Session Process Id 2230, DISPLAY=:0

Any reason for dot-naming the functions?

Any reason for dot-naming the functions?

When you normally source a script file in shell, all functions declared in global scope get declared and become available to call in that shell session (as commands). In some shells (can't remember how bash acts by default) prefixing function with a dot prevents that behavior (I heard people calling those "hidden functions").