The command add-apt-repository is used for adding PPA reference to our Ubuntu or Debian systems. For newer installations this command may not available in your system. Use following commands to add this command utility in your system as per your operating systems.
Ubuntu and Debian 7 (Wheezy) or Earlier Versions:
For Ubuntu Systems and Debian 7 (Wheezy) or its earlier versions add-apt-repository command is available under python-software-properties package. Use the following command to install it.
$ sudo apt-get install python-software-properties
Debian 8 (Jessie) or Later Versions:
In Debian 8 (Jessie) add-apt-repository command utility is available under software-properties-common package. So use following command to install it.
$ sudo apt-get install software-properties-common