Adapted from arch-by-hand, more bare bones.

install_efi_arch.sh

#!/bin/bash

# This script is designed to be run in conjunction with a UEFI boot using Archboot intall media.

# prereqs:
# --------------------
# EFI "BIOS" set to boot *only* from EFI
# successful EFI boot of Archboot USB
# mount -t vfat /dev/sdb1 /src

set -o nounset
HOSTNAME=egg
USERNAME=mig

DISK=/dev/sda
AURHELPER=packer
INSTALL_TARGET="/install"
HR="--------------------------------------------------------------------------------"
PACMAN="pacman --noconfirm --config /tmp/pacman.conf"
TARGET_PACMAN="pacman --noconfirm --config /tmp/pacman.conf --root "${INSTALL_TARGET}""
CHROOT_PACMAN="pacman --noconfirm --cachedir /var/cache/pacman/pkg --config /tmp/pacman.conf"
FILE_URL="file:///packages/core-$(uname -m)/pkg"
FTP_URL='ftp://mirrors.kernel.org/archlinux/$repo/os/$arch'
HTTP_URL='http://mirrors.kernel.org/archlinux/$repo/os/$arch'

SetValue () { 
  # EXAMPLE: SetValue VARIABLENAME '\"Quoted Value\"' /file/path

  VALUENAME="$1" NEWVALUE="$2" FILEPATH="$3"
  sed -i "s+^#\?\(${VALUENAME}\)=.*$+\1=${NEWVALUE}+" "${FILEPATH}"
}

CommentOutValue () {
  VALUENAME="$1" FILEPATH="$2"
  sed -i "s/^\(${VALUENAME}.*\)$/#\1/" "${FILEPATH}"
}

UncommentValue () {
  VALUENAME="$1" FILEPATH="$2"
  sed -i "s/^#\(${VALUENAME}.*\)$/\1/" "${FILEPATH}"
}

echo "STARTING"

echo -n "Waiting for network address.."
dhcpcd -p eth0

# Mount packages squashfs images
# ------------------------------------------------------------------------
umount "/packages/core-$(uname -m)"
umount "/packages/core-any"
rm -rf "/packages/core-$(uname -m)"
rm -rf "/packages/core-any"

mkdir -p "/packages/core-$(uname -m)"
mkdir -p "/packages/core-any"

modprobe -q loop
modprobe -q squashfs
mount -o ro,loop -t squashfs "/src/packages/archboot_packages_$(uname -m).squashfs" "/packages/core-$(uname -m)"
mount -o ro,loop -t squashfs "/src/packages/archboot_packages_any.squashfs" "/packages/core-any"

# Create temporary pacman.conf file
# ------------------------------------------------------------------------
cat << PACMANEOF > /tmp/pacman.conf
[options]
Architecture = auto
CacheDir = ${INSTALL_TARGET}/var/cache/pacman/pkg
CacheDir = /var/cache/pacman/pkg
CacheDir = /packages/core-$(uname -m)/pkg
CacheDir = /packages/core-any/pkg

[core]
Server = ${FILE_URL}
Server = ${FTP_URL}
Server = ${HTTP_URL}

[extra]
Server = ${FILE_URL}
Server = ${FTP_URL}
Server = ${HTTP_URL}

PACMANEOF

${PACMAN} -Sy

echo -e "\nInstalling prereqs...\n$HR"
echo "Server = http://mirror.ece.vt.edu/archlinux/$repo/os/$arch" >> /etc/pacman.d/mirrorlist
${PACMAN} -Sy gptfdisk btrfs-progs

echo -e "\nFormatting disk...\n$HR"

# disk prep
sgdisk -Z ${DISK} # zap all on disk
sgdisk -a 2048 -o ${DISK} # new gpt disk 2048 alignment

# create partitions
sgdisk -n 1:0:+512M ${DISK} # partition 1 (UEFI SYS), default start block, 512MB
sgdisk -n 2:0:+400M ${DISK} # partition 2 (BOOT), default start block, 400MB
sgdisk -n 3:0:+16G  ${DISK} # partition 3 (SWAP), default start block, 16GB
sgdisk -n 4:0:+20G  ${DISK} # partition 4 (ROOT), default start, 20G
sgdisk -n 5:0:+20G  ${DISK} # partition 4 (VAR),  default start, 20G
sgdisk -n 6:0:+50G  ${DISK} # partition 5 (USR),  default start, 50G
sgdisk -n 7:0:0     ${DISK} # partition 6 (LUKS), default start, remaining

# set partition types
sgdisk -t 1:ef00 ${DISK}
sgdisk -t 2:8300 ${DISK}
sgdisk -t 3:8200 ${DISK}
sgdisk -t 4:8300 ${DISK}
sgdisk -t 5:8300 ${DISK}
sgdisk -t 6:8300 ${DISK}
sgdisk -t 7:8300 ${DISK}

# label partitions
sgdisk -c 1:"UEFISYS" ${DISK}
sgdisk -c 2:"BOOT" ${DISK}
sgdisk -c 3:"SWAP" ${DISK}
sgdisk -c 4:"ROOT" ${DISK}
sgdisk -c 5:"VAR"  ${DISK}
sgdisk -c 6:"USR"  ${DISK}
sgdisk -c 7:"LUKS" ${DISK}

# format LUKS on root
cryptsetup --cipher=aes-xts-plain --verify-passphrase --key-size=512 luksFormat "${DISK}7"
cryptsetup luksOpen "${DISK}7" root

# NOTE: make sure to add dm_crypt and aes_x86_64 to MODULES in rc.conf

# make filesystems
echo -e "\nCreating Filesystems...\n$HR"

mkfs.vfat -F32 -n "UEFISYS" "${DISK}1"
mkfs.ext3 -L "BOOT" "${DISK}2"
mkswap -L "SWAP" "${DISK}3"
swapon "${DISK}3"
mkfs.ext4 -L "ROOT" "${DISK}4"
mkfs.ext4 -L "VAR" "${DISK}5"
mkfs.ext4 -L "USR" "${DISK}6"
mkfs.ext4 -L "HOME" /dev/mapper/home

# mount target
mkdir "${INSTALL_TARGET}"
mount -t ext4 "${DISK}4" "${INSTALL_TARGET}"
mount -t ext4 "${DISK}5" "${INSTALL_TARGET}"/var
mount -t ext4 "${DISK}6" "${INSTALL_TARGET}"/usr
mount -t ext4 /dev/mapper/home "${INSTALL_TARGET}"/home
mkdir "${INSTALL_TARGET}"/boot
mount -t ext3 "${DISK}2" "${INSTALL_TARGET}"/boot
mkdir "${INSTALL_TARGET}"/boot/efi
mount -t vfat "${DISK}1" "${INSTALL_TARGET}"/boot/efi

# kernel modules for EFI install
# ------------------------------------------------------------------------

if [[ "$(cat "/sys/class/dmi/id/sys_vendor")" == 'Apple Inc.' ]] || [[ "$(cat "/sys/class/dmi/id/sys_vendor")" == 'Apple Computer, Inc.' ]]; then
    modprobe -r -q efivars || true
else
    modprobe -q efivars
fi

modprobe -q dm-mod

# ------------------------------------------------------------------------
# mount proc, sys, dev in install root
# ------------------------------------------------------------------------
mkdir -p "${INSTALL_TARGET}"/proc
mkdir -p "${INSTALL_TARGET}"/sys
mkdir -p "${INSTALL_TARGET}"/dev

mount -o bind /proc "${INSTALL_TARGET}"/proc
mount -o bind /sys "${INSTALL_TARGET}"/sys
mount -o bind /dev "${INSTALL_TARGET}"/dev

mkdir -m 755 -p "${INSTALL_TARGET}"/tmp
cp /tmp/pacman.conf "${INSTALL_TARGET}"/tmp/pacman.conf

# ------------------------------------------------------------------------
# Install base, necessary utilities
# ------------------------------------------------------------------------
[[ ! -d "${INSTALL_TARGET}/var/cache/pacman/pkg" ]] && mkdir -m 755 -p "${INSTALL_TARGET}/var/cache/pacman/pkg"
[[ ! -d "${INSTALL_TARGET}/var/lib/pacman" ]] && mkdir -m 755 -p "${INSTALL_TARGET}/var/lib/pacman"

${TARGET_PACMAN} -Sy

${TARGET_PACMAN} -Su base curl

${TARGET_PACMAN} -R grub
cp -r "${INSTALL_TARGET}"/boot/grub "${INSTALL_TARGET}"/boot/grub.bak
rm -rf "${INSTALL_TARGET}"/boot/grub
${TARGET_PACMAN} -S grub2-efi-x86_64

# ------------------------------------------------------------------------
# Configure new system
# ------------------------------------------------------------------------
SetValue HOSTNAME "${HOSTNAME}" "${INSTALL_TARGET}"/etc/rc.conf
sed -i "s/^\(127\.0\.0\.1.*\)$/\1 ${HOSTNAME}/" "${INSTALL_TARGET}"/etc/hosts
SetValue CONSOLEFONT Lat2-Terminus16 "${INSTALL_TARGET}"/etc/rc.conf

# ------------------------------------------------------------------------
# write fstab
# ------------------------------------------------------------------------
# You can use UUID's or whatever you want here, of course. This is just
# the simplest approach and as long as your drives aren't changing values
# randomly it should work fine.
cat > "${INSTALL_TARGET}"/etc/fstab <<FSTAB_EOF
/dev/sda1 /boot/efi vfat defaults 0 0
/dev/sda2 /boot ext3 defaults 0 1
/dev/sda3 none swap defaults 0 0
/dev/sda4 / ext4 defaults 0 1
/dev/sda5 /usr ext4 defaults 0 1
/dev/sda6 /var ext4 defaults 0 1
/dev/mapper/home /home ext4 defaults,noatime 0 1 
tmpfs /tmp tmpfs nodev,nosuid 0	0
FSTAB_EOF

# ------------------------------------------------------------------------
# copy configs we want to carry over to target from install environment
# ------------------------------------------------------------------------

mv "${INSTALL_TARGET}"/etc/resolv.conf "${INSTALL_TARGET}"/etc/resolv.conf.orig
cp /etc/resolv.conf "${INSTALL_TARGET}"/etc/resolv.conf

# we have to remount /boot from inside the chroot
umount "${INSTALL_TARGET}"/boot/efi
umount "${INSTALL_TARGET}"/boot

# ------------------------------------------------------------------------
# Create install_efi script (to be run *after* chroot /install)
# ------------------------------------------------------------------------

touch "${INSTALL_TARGET}"/install_efi
chmod a+x "${INSTALL_TARGET}"/install_efi
cat > "${INSTALL_TARGET}"/install_efi <<EFI_EOF

SetValue () { VALUENAME="\$1" NEWVALUE="\$2" FILEPATH="\$3"; sed -i "s+^#\?\(\${VALUENAME}\)=.*\$+\1=\${NEWVALUE}+" "\${FILEPATH}"; }
CommentOutValue () { VALUENAME="\$1" FILEPATH="\$2"; sed -i "s/^\(\${VALUENAME}.*\)\$/#\1/" "\${FILEPATH}"; }
UncommentValue () { VALUENAME="\$1" FILEPATH="\$2"; sed -i "s/^#\(\${VALUENAME}.*\)\$/\1/" "\${FILEPATH}"; }

mkdir -p /boot
mount -t ext3 /dev/sda2 /boot

mkdir -p /boot/efi
mount -t vfat /dev/sda1 /boot/efi

SetValue MODULES '\\"dm_mod dm_crypt aes_x86_64 ext2 ext4 vfat intel_agp drm i915\\"' /etc/mkinitcpio.conf
SetValue HOOKS '\\"base udev pata scsi sata usb usbinput keymap consolefont encrypt filesystems usr\\"' /etc/mkinitcpio.conf
mkinitcpio -p linux

UncommentValue en_US /etc/locale.gen
locale-gen

SetValue GRUB_CMDLINE_LINUX '\\"root=/dev/sda4 add_efi_memmap i915.modeset=1 i915.i915_enable_rc6=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1 pcie_aspm=force quiet\\"' /etc/default/grub
SetValue GRUB_TERMINAL_OUTPUT gfxterm /etc/default/grub
SetValue GRUB_GFXMODE 960x600x32,auto /etc/default/grub
SetValue GRUB_GFXPAYLOAD_LINUX keep /etc/default/grub

mkdir -p /boot/efi/EFI

grub-install --directory=/usr/lib/grub/x86_64-efi --target=x86_64-efi  --efi-directory=/boot/efi --bootloader-id=arch_grub --boot-directory=/boot --recheck --debug &>/boot/grub_uefi.log

if [[ "\$(cat "/sys/class/dmi/id/sys_vendor")" != 'Apple Inc.' ]] && [[ "\$(cat "/sys/class/dmi/id/sys_vendor")" != 'Apple Computer, Inc.' ]]; then
    for _bootnum in \$(efibootmgr | grep '^Boot[0-9]' | fgrep -i 'ARCH LINUX (GRUB2)' | cut -b5-8) ; do
        efibootmgr --bootnum "\${_bootnum}" --delete-bootnum
    done
    
    efibootmgr --verbose --create --gpt --disk /dev/sda --part 1 --write-signature --label 'ARCH LINUX (GRUB2)' --loader '\\EFI\\arch_grub\\grubx64.efi'
fi

grub-mkconfig -o /boot/grub/grub.cfg

exit
EFI_EOF

chroot "${INSTALL_TARGET}" /install_efi

touch "${INSTALL_TARGET}"/post_install
chmod a+x "${INSTALL_TARGET}"/post_install
cat > "${INSTALL_TARGET}"/post_install <<POST_EOF
set -o errexit
set -o nounset

SetValue () { VALUENAME="\$1" NEWVALUE="\$2" FILEPATH="\$3"; sed -i "s+^#\?\(\${VALUENAME}\)=.*\$+\1=\${NEWVALUE}+" "\${FILEPATH}"; }
CommentOutValue () { VALUENAME="\$1" FILEPATH="\$2"; sed -i "s/^\(\${VALUENAME}.*\)\$/#\1/" "\${FILEPATH}"; }
UncommentValue () { VALUENAME="\$1" FILEPATH="\$2"; sed -i "s/^#\(\${VALUENAME}.*\)\$/\1/" "\${FILEPATH}"; }

echo -e "${HR}\\nNew root user password\\n${HR}"
passwd

echo -e "${HR}\\nNew non-root user password (username:${USERNAME})\\n${HR}"
groupadd sudo
useradd -m -g users -G audio,lp,optical,storage,video,games,power,scanner,network,sudo,wheel -s /bin/bash ${USERNAME}
passwd ${USERNAME}

mv /etc/profile.d/locale.sh /etc/profile.d/locale.sh.preupdate || true

pacman --noconfirm -Syu
pacman --noconfirm -S base-devel

mkdir -p /tmp/build
cd /tmp/build
wget https://aur.archlinux.org/packages/${AURHELPER}/${AURHELPER}.tar.gz
tar -xzvf ${AURHELPER}.tar.gz
cd ${AURHELPER}
makepkg --asroot -si
cd /tmp

pacman --noconfirm -S sudo
cp /etc/sudoers /tmp/sudoers.edit
sed -i "s/#\s*\(%wheel\s*ALL=(ALL)\s*ALL.*$\)/\1/" /tmp/sudoers.edit
sed -i "s/#\s*\(%sudo\s*ALL=(ALL)\s*ALL.*$\)/\1/" /tmp/sudoers.edit
visudo -qcsf /tmp/sudoers.edit && cat /tmp/sudoers.edit > /etc/sudoers 

pacman --noconfirm -S acpi acpid cpufrequtils
${AURHELPER} --noconfirm -S acpitool powertop2
sed -i "/^DAEMONS/ s/)/ @acpid)/" /etc/rc.conf
sed -i "/^MODULES/ s/)/ acpi-cpufreq cpufreq_ondemand cpufreq_powersave coretemp)/" /etc/rc.conf
echo "/etc/acpi/handler.sh boot" > /etc/rc.local

pacman --noconfirm -S ntp
sed -i "/^DAEMONS/ s/hwclock /!hwclock @ntpd /" /etc/rc.conf

pacman --noconfirm -S iw wpa_supplicant rfkill
pacman --noconfirm -S netcfg wpa_actiond ifplugd
mv /etc/wpa_supplicant.conf /etc/wpa_supplicant.conf.orig
echo -e "ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=network\nupdate_config=1" > /etc/wpa_supplicant.conf
sed -i "/^DAEMONS/ s/)/ @net-auto-wireless @net-auto-wired)/" /etc/rc.conf
sed -i "/^DAEMONS/ s/ network / /" /etc/rc.conf
echo "options iwlagn led_mode=2" > /etc/modprobe.d/iwlagn.conf

pacman --noconfirm -S alsa-utils alsa-plugins
sed -i "/^DAEMONS/ s/)/ @alsa)/" /etc/rc.conf
mv /etc/asound.conf /etc/asound.conf.orig || true

pacman --noconfirm -S base-devel mesa mesa-demos
pacman --noconfirm -S xorg xorg-server xorg-xinit xorg-utils xorg-server-utils xdotool xorg-xlsfonts

pacman --noconfirm -S xcompmgr xscreensaver hsetroot
pacman --noconfirm -S rxvt-unicode urxvt-url-select
pacman --noconfirm -S dbus upower
sed -i "/^DAEMONS/ s/)/ @dbus)/" /etc/rc.conf

pacman --noconfirm -S wireless_tools netcfg-vpnc

pacman --noconfirm -S terminus-font
${AURHELPER} --noconfirm -S webcore-fonts
${AURHELPER} --noconfirm -S libspiro
${AURHELPER} --noconfirm -S fontforge
${AURHELPER} -S freetype2-infinality fontconfig-infinality

pacman --noconfirm -S htop openssh keychain bash-completion git vim
pacman --noconfirm -S chromium flashplugin
${AURHELPER} -S --noconfirm terminus-font-ttf

POST_EOF

chroot "${INSTALL_TARGET}" /post_install
mv "${INSTALL_TARGET}"/post_install /.