notify-send

Uses the current desktop environment's notification system to create a notification.

Show a notification with the title "Test" and the content "This is a test":

notify-send "{{Test}}" "{{This is a test}}"

Show a notification with a custom icon:

notify-send -i {{icon.png}} "{{Test}}" "{{This is a test}}"

Show a notification for 5 seconds:

notify-send -t 5000 "{{Test}}" "{{This is a test}}"

Show a notification with an app's icon:

notify-send "{{Test}}" --icon={{google-chrome}}