Check if an apt-get package is installed and then install it if it's not on Linux

Question

I\'m working on a Ubuntu system and currently this is what I\'m doing:

if ! which command > /dev/null; then
   echo -e \"Command not found! Install? (y/n)         


        

Answer 1

This command is the most memorable:

dpkg --get-selections <package-name>

If it's installed it prints:

<package-name> install

Otherwise it prints

No packages found matching <package-name>.

This was tested on Ubuntu 12.04.1 (Precise Pangolin).

Answer 2

It seems that nowadays apt-get has an option --no-upgrade that just does what the OP wants:

--no-upgrade Do not upgrade packages. When used in conjunction with install, no-upgrade will prevent packages listed from being upgraded if they are already installed.

Manpage from https://linux.die.net/man/8/apt-get

Therefore you can use

apt-get install --no-upgrade package

and package will be installed only if it's not.

Answer 3

Many things has been told but for me simplest way is:

dpkg -l | grep packagename

Answer 4

This will do it. apt-get install is idempotent.

sudo apt-get install command