pi@raspberrypi:~ $ rar
bash: rar: command not found
pi@raspberrypi:~ $ sudo apt install unrar
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package unrar is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'unrar' has no installation candidate
pi@raspberrypi:~ $ sudo apt install rar
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package rar is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'rar' has no installation candidate
pi@raspberrypi:~ $