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've found all solutions above can produce a false positive if a package is installed and then removed yet the installation package remains on the system.

To replicate: Install package apt-get install curl
Remove package apt-get remove curl

Now test above answers.

The following command seems to solve this condition:
dpkg-query -W -f='${Status}\n' curl | head -n1 | awk '{print $3;}' | grep -q '^installed$'

This will result in a definitive installed or not-installed