Terminal: sudo: apt-get: command not found

The short answer:

Re-install Ubuntu from a Live CD or USB.

The long version:

The long version would be a waste of your time: your system will never be clean, but if you insist you could try:

• copying everything (missing) except for the /home folder from the Live CD/USB to your HDD.

OR

• do a re-install/repair over the broken system again with the Live CD / USB stick.

OR

• download the deb file for apt-get and install as explained on above posts.

I would definitely go for a fresh new install as there are so many things to do and so little time.

I faced the same issue regarding apt-get: command not found here are the steps how I resolved it on Ubuntu Xenial

• Search the appropriate version of apt from here (apt_1.4_amd64.deb for ubuntu xenial)

• Download the apt.deb

  wget http://security.ubuntu.com/ubuntu/pool/main/a/apt/apt_1.4_amd64.deb
  

• Install the apt.deb package

  sudo dpkg -i apt_1.4_amd64.deb
  

Now we can easily run

sudo apt-get install <Package_Name>