I am not sure I fully understand your question. There are no updates to files
in Linux, only to packages. If you wish to check which update might change a specific file you have in mind, you can do it like this.
First, this command
sudo apt-get upgrade --dry-run
will provide you with a list of packages to be upgraded, without performing any
operation. The following command will then only download the packages in question
sudo apt-get upgrade --download-only
Now that you have you packages safely in your vault (which, BTW, is located at /var/cache/apt/archives) you may check the files any package will have to update by
means of the command
dpkg-deb -c package_name.deb
The -c
option means this:
-c, --contents archive
Lists the contents of the filesystem tree archive portion of the package archive. It is
currently produced in the format generated by tar's verbose listing.
When you are satisfied all is well, you may install the package with
sudo dpkg -i package_name.deb
All of this can be easily scripted, of course. I hope this is what you were after.