pkgfile

pkgfile is a tool that tells you which package owns a specified file or which files a given package provides.

You can install it with pkgfile from the official repositories or with pkgfile-git^AUR from the Arch User Repository.

After installing the package, you should update the file list database as root:

# pkgfile --update

Example:

$ pkgfile makepkg     # Search for a package that contains a file named 'makepkg'.
core/pacman           # Your searched file is in the 'pacman' package in the [core] repository.

Example 2:

$ pkgfile --list core/pacman      # List all files provided by the 'pacman' package in the [core] repository.