How to make Ansible execute a shell script if a package is not installed

Question

How can I make Ansible execute a shell script if a (rpm) package is not installed? Is it somehow possible to leverage the yum module?

Answer 1

You shouldn't be using dpkg -l package because it has no idea if your package has been removed or is still installed.
Instead it's probably better to use dpkg -s package.

To check if the package is installed :
- shell: dpkg -s package | grep 'install ok installed'
or if you don't mind the package on hold or other states :
- shell: dpkg -s package | grep 'installed'
This return 0 when installed and 1 if not.

(It's important to use the shell as we are using a pipe |)