notify-send

A program to send desktop notifications, inform the user about an event or display some form of information without getting in the user’s way.

Syntax 
      notify-send [OPTIONS] summary [body]
 
Key
   -u, --urgency=LEVEL
               The urgency level (low,  normal,  critical).
 
   -t, --expire-time=TIME
               The  timeout in milliseconds at which to expire the
               notification.
 
   -i, --icon=ICON[,ICON...]
               An icon filename or stock icon to display.
 
   -c, --category=TYPE[,TYPE...]
               Specifies the notification category.
 
   -?, --help
               Show a help message
 
   -h, --hint=TYPE:NAME:VALUE
               Pass extra data. Valid TYPEs are int, double, string and byte.

To use notify-send, you might need to install the following package:
$ sudo apt-get install libnotify-bin

Examples

$ notify-send "Hello World"

$ notify-send -t 5000 -u low "Hello World"

The return status is zero if all information was written successfully.

“Those who know, do not speak. Those who speak, do not know” ~ The Tao

Related Linux commands

echo - Display message on screen.
Equivalent Windows command: IF - Conditionally perform a command.