APT Ubuntu

* apt-get is a powerful command line tool used with ubuntu advanced packaging tool(APT) for performing functions like


                                            + Installation of new software packages
                                            +  Upgrading of existing software packages
                                            + removal of software packages
                                            + updating software packages list/index
                                            + even upgrading whole system


* Examples :
                       + installation of new software package
                           sudo apt-get install <software-package>
                       + removing a package
                           sudo apt-get remove <software-package>
         NOTE: For removing or adding multiple packages
                      sudo apt-get install/remove <sp1> <sp2> ... <spn>
                    package name should be seprated by space.
what is APT package index?
APT package index is database of available packages in repositories listed in /etc/apt/source.list file. So time to time we have to update our repositories so that new software packages can also be listed in it.
                       + Updating repository
                           sudo apt-get update
                       + Upgrading software package : If we want to upgrade our software to newest version we do it as follows:
                           sudo apt-get upgrade (will upgrade all software packages)
                           sudo apt-get install <sp> : will upgrade latest version of sp if already installed otherwise  it will install the latest version of <sp>.
                      + Purge: removal of package with package configuration files also , whereas remove only removes package without any configuration files.
                          sudo apt-get purge <sp>
where sp : denotes name of software package like vlc, skype etc
 

* Aptitude:
is a menu driven text based front end for APT. Like apt-get it also perform package management functions like installation, removal, up gradation etc.
sudo aptitude : on terminal give u a menu based representation of packages under different categories. like packages installed, packages not installed, packages upgraded etc.
Suppose u want to install a package, then goto not installed package option, select specified package and then enter +, the package entry turns green means it is marked for installation. Similarly for removal , up gradation options.
So in short we can say:
       Aptitude = textual version of synaptic package

Note : To exit from aptitude enter 'q' it will ask for confirmation.