Pacman option to assume "yes" to every question?

From man pacman:

--noconfirm
Bypass any and all “Are you sure?” messages. It’s not a good idea to do this unless you want to run pacman from a script.

Note the qualification about using this with care...

Arch is a rolling release, which means pacman has to, from time to time, manage some quite complex upgrades. At these times pacman will prompt you to confirm your choices—disregarding these prompts will generally not be a significant issue, but in some cases, as with the recent move from /lib to /usr/lib , a lack of attention will cause major breakage. This is a not a habit you want to cultivate.

While the manpage on the matter is not very clear, the --noconfirm flag will not assume "yes" on every answer. It assumes the default answer which can be "no" sometimes.

--noconfirm
      Bypass any and all “Are you sure?” messages. It’s not a good idea
      to do this unless you want to run pacman from a script

To assume "yes", you could pipe the output of the yes command to pacman.

yes | sudo pacman -S firefox