#The sudo apt-get update command is used to download package 
#information from all configured sources 
#So when you run update command, it downloads the package 
#information from the Internet. It is useful to get info on 
#an updated version of packages or their dependencies.

sudo apt-get update
sudo apt-get install zsh

#Now that ZSH shell is installed, you can check whether ZSH 
#is working with the following command:
zsh --version

$ sudo apt-get install zsh
$ sh -c "$(wget https://raw.github.com/robbyrussell/oh-my-zsh/master/tools/install.sh -O -)"