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

I offer this update since Ubuntu added its "Personal Package Archive" (PPA) just as this question was answered, and PPA packages have a different result.

1. Native Debian repository package not installed:

   ~$ dpkg-query -l apache-perl
   ~$ echo $?
   1
   

2. PPA package registered on host and installed:

   ~$ dpkg-query -l libreoffice
   ~$ echo $?
   0
   

3. PPA package registered on host but not installed:

   ~$ dpkg-query -l domy-ce
   ~$ echo $?
   0
   ~$ sudo apt-get remove domy-ce
   [sudo] password for user: 
   Reading package lists... Done
   Building dependency tree       
   Reading state information... Done
   Package domy-ce is not installed, so not removed
   0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
   

Also posted on: https://superuser.com/questions/427318/test-if-a-package-is-installed-in-apt/427898