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Final solution not requiring to be root, and accessible from a non-interactive shell in an automated way and more advanced and usable than possible duplicate link provided earlier :

-XAUTHORITY :

ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^XAUTHORITY=' 

• DISPLAY :

  ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^DISPLAY='

The snippet list all user's pids, iterate over them, then break on the first match

Based on this

Final solution not requiring to be root, and accessible from a non-interactive shell in an automated way and more advanced and usable than possible duplicate link provided earlier :

-XAUTHORITY :

ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^XAUTHORITY=' 

• DISPLAY :

  ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^DISPLAY='

The snippet list all user's pids, iterate over them, then break on the first match

Based on this

Final solution not requiring to be root, and accessible from a non-interactive shell in an automated way and more advanced and usable than possible duplicate link provided earlier :

-XAUTHORITY :

ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^XAUTHORITY=' 

• DISPLAY :

  ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^DISPLAY=:.*$'

The snippet list all user's pids, iterate over them, then break on the first match

Based on this

Final solution not requiring to be root, and accessible from a non-interactive shell in an automated way and more advanced and usable than possible duplicate link provided earlier :

-XAUTHORITY :

ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^XAUTHORITY=' 

• DISPLAY :

  ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^DISPLAY='

The snippet list all user's pids, iterate over them, then break on the first match

Based on this

Final solution not requiring to be root, and accessible from a non-interactive shell in a automated way :

-XAUTHORITY :

ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^XAUTHORITY=' 

• DISPLAY :

  ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^DISPLAY=:.*$'

Based on this

Final solution not requiring to be root, and accessible from a non-interactive shell in an automated way and more advanced and usable than possible duplicate link provided earlier :

-XAUTHORITY :

ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^XAUTHORITY=' 

• DISPLAY :

  ps -u $(id -u) -o pid= | xargs -I{} cat /proc/{}/environ 2>/dev/null | tr '\0' '\n' | grep -m1 '^DISPLAY=:.*$'

The snippet list all user's pids, iterate over them, then break on the first match

Based on this