pkgfile is a tool that tells you which package owns a specified file or which files a given package provides.
After installing the package, you should update the file list database as root:
# pkgfile --update
$ 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.
$ pkgfile --list core/archlinux-keyring # List all files provided by the 'archlinux-keyring' package in the [core] repository.
core/archlinux-keyring usr/ core/archlinux-keyring usr/share/ core/archlinux-keyring usr/share/pacman/ core/archlinux-keyring usr/share/pacman/keyrings/ core/archlinux-keyring usr/share/pacman/keyrings/archlinux-revoked core/archlinux-keyring usr/share/pacman/keyrings/archlinux-trusted core/archlinux-keyring usr/share/pacman/keyrings/archlinux.gpg
"Command not found" hook
pkgfile includes a "command not found" hook that will automatically search the official repositories, if you enter an unrecognized command.
To enable it in all children shells, you need to source the hook from one of your shell initialization files. E.g. for Bash:
And for Zsh: