Install zsh if it isn't available then clone/setup prezto and change the shell. Just curl && exec it

.install_prezto

#!/bin/bash

N_ZSH="\n zsh not found. Installing it\n" # Not found
Y_ZSH="\n zsh found. Cloning prezto\n"    # Yes found :P

install_zsh (){
    sudo apt-get update && sudo apt-get -y install zsh
}

clone_prezto (){
    /bin/zsh - <<'EOF'
    echo -e "\033[1;34m\n Cloning prezto\n\033[0m"
    git clone --recursive https://github.com/sorin-ionescu/prezto.git \
    "${ZDOTDIR:-$HOME}/.zprezto"
EOF
}

set_prezto (){
    /bin/zsh - <<'EOF'
    echo -e "\033[1;34m\n Setting up prezto\n\033[0m"
    setopt EXTENDED_GLOB
    for rcfile in "${ZDOTDIR:-$HOME}"/.zprezto/runcoms/^README.md(.N); do
        ln -s "$rcfile" "${ZDOTDIR:-$HOME}/.${rcfile:t}"
    done
EOF
}

cd "$HOME" || echo $'Can\'t cd into $HOME' && exit 1

# Is zsh installed?
if [ "$(which zsh)" != 0 ]
then
    echo -e "\033[1;31m${N_ZSH}\033[0m"
    install_zsh && clone_prezto && set_prezto
else
    echo -e "\033[1;34m${Y_ZSH}\033[0m"
    clone_prezto && set_prezto
fi

exit 0