Ensure script can run a command as root

script.sh

#!/bin/sh
# Source: https://get.docker.com/

command_exists() {
	command -v "$@" > /dev/null 2>&1
}

sh_c='sh -c'
	if [ "$user" != 'root' ]; then
		if command_exists sudo; then
			sh_c='sudo -E sh -c'
		elif command_exists su; then
			sh_c='su -c'
		else
			cat >&2 <<-'EOF'
			Error: this installer needs the ability to run commands as root.
			We are unable to find either "sudo" or "su" available to make this happen.
			EOF
			exit 1
		fi
	fi

# now run some command as root
$sh_c 'some command...'