It sounds like the file command is not installed on your system. To install it, you will need to use a package manager. If you are using a Debian-based Linux distribution (such as Ubuntu), you can use the apt command to install file like this:
sudo apt update sudo apt install file
This will download and install the file package from the default package repository. Once it is installed, you should be able to use the file command.
If you are using a different Linux distribution, the exact steps to install file will depend on your distribution and the package manager it uses. Consult the documentation for your distribution for more information.