For my own documentation I repost this stackoverflow. I’m using ubuntu 14.04 in this case.
Suddenly after I wrongly downgraded my libapt version, everytime we do the apt or apt-get it replied with symbol lookup error: apt-get: undefined symbol.
symbol lookup error: apt-get: undefined symbol: _ZN11CommandLine10GetCommandEPKNS_8DispatchEjPKPKc
Then how to resolved it :
Try this first :
sudo apt-get install --reinstall apt
I tried it myself, no risk to your system.
If it doesn’t work, you’ll have to get the package from http://packages.ubuntu.com/.
Choose the good one for your distribution. And install it with dpkg :
sudo dpkg -i apt_#version#.deb
Everything should work fine but I didn’t have tested this.