1. Go to https://sslvpn.demo.sonicwall.com/cgi-bin/welcome
2. Login using demo:password
3. To download tar.gz with client click on NetExtender icon
4. Create symbolic links, on 32 bit linux:

sudo ln -s /lib/i386-linux-gnu/libssl.so.1.0.0 /usr/lib/libssl.so.6
sudo ln -s /lib/i386-linux-gnu/libcrypto.so.1.0.0 /usr/lib/libcrypto.so.6

on 64 bit linux:

sudo ln -s /lib/x86_64-linux-gnu/libssl.so.1.0.0 /usr/lib/libssl.so.6
sudo ln -s /lib/x86_64-linux-gnu/libcrypto.so.1.0.0 /usr/lib/libcrypto.so.6

5. Extract the client, make install script executable and run it as root
Now you can use one of these commands:

sudo netExtenderGui
sudo netExtender

In a bash script you could use:

sudo netExtender -u user -p password -d domain server

But it should be evident that this is not a very secure method as it needs to be run as root (or pppd run as root – see prompt during installation), and the password as well as the user are stored in plain text in the shell history and who knows where else.
Maybe using the GUI or the interactive CLI tool is better?