This is a demo script used at Alpine Linux booth at LinuxDays 2017 to demonstrate how is apk-tools and Alpine Linux awesome. Recorded output: https://asciinema.org/a/141360

apk-chroot-installation-demo.sh

#!/bin/sh
# vim: set ts=4:
#
# Any copyright is dedicated to the Public Domain.
# http://creativecommons.org/publicdomain/zero/1.0/
#
set -eu

APK_KEY_URI='https://alpinelinux.org/keys/alpine-devel@lists.alpinelinux.org-4a6a0840.rsa.pub'
APK_KEY_SHA1='3af08548ef78cfdedcf349880c2c6a1a48763a0e'
APK_TOOLS_URI='https://github.com/alpinelinux/apk-tools/releases/download/v2.7.2/apk-tools-2.7.2-x86_64-linux.tar.gz'
APK_TOOLS_SHA1='f77512787d94e223414c46749b0aaefc15e2914f'
ALPINE_REPOS='https://cz.alpinelinux.org/alpine/v3.6/main
https://cz.alpinelinux.org/alpine/v3.6/community'

ESC_RESET='\033[0m'
ESC_BOLD='\033[1m'
ESC_DIM='\033[2m'
ESC_RED='\033[31m'
ESC_GREEN='\033[32m'
ESC_YELLOW='\033[33m'
ESC_BLUE='\033[34m'
ESC_MANGENTA='\033[35m'
ESC_CYAN='\033[36m'
ESC_WHITE='\033[37m'

TYPING_SPEED=30
PROMPT="$ESC_RED$(hostname) #$ESC_RESET"

# Unmounts all filesystem under the specified directory tree.
umount_recursively() {
	local mount_point="$1"
	test -n "$mount_point" || return 1

	cat /proc/mounts \
		| cut -d ' ' -f 2 \
		| grep "^$mount_point" \
		| sort -r \
		| xargs -r umount -rn
}

typing() {
	if [ $# -eq 0 ]; then
		cat | pv -qL $TYPING_SPEED
	else
		printf '%s\n' "$@" | pv -qL $TYPING_SPEED
	fi
}

hr() {
	printf '~%.0s' $(seq 1 80)
	printf '\n'
}

blank() {
	local count=${1:-1}
	printf '\n%.0s' $(seq 1 $count)
}

say() {
	printf "$ESC_BOLD$ESC_YELLOW"
	hr
	typing "$@"
	hr
	printf "$ESC_RESET\n"
}

run() {
	printf "$PROMPT ${ESC_BOLD}"
	typing "$*"
	printf "$ESC_RESET"

	if [ $# -eq 1 ]; then
		eval "$@"
	else
		"$@"
	fi
}


#------------------------------  M a i n  ------------------------------

temp_dir=$(mktemp -d)

cleanup() {
	set +e

	echo 'Cleaning up...' >&2
	umount_recursively "$temp_dir"
	rm -Rf "$temp_dir"
}
trap cleanup EXIT HUP INT TERM


cd "$temp_dir"

say <<-EOF
	It's extremely easy to create a rootfs with Alpine Linux, i.e. install
	Alpine inside chroot, container or create a custom VM image.
	All you need is just apk-tools (Alpine's package manager) which you can
	download also as a statically linked binary.

	I will show you how...

	>> Please note that this is NOT a video, it's a script running in a loop. <<
EOF
blank

sleep 2

say <<-EOF
	Okay, first we download statically linked apk-tools...
EOF

run wget -T 3 -q "$APK_TOOLS_URI"
run "echo '$APK_TOOLS_SHA1  ${APK_TOOLS_URI##*/}' | sha1sum -c || exit 1"
run tar --strip-components 1 -xzf "${APK_TOOLS_URI##*/}"
blank

say 'And GPG key to verify packages...'

run wget -q "$APK_KEY_URI"
run 'echo "$APK_KEY_SHA1  ${APK_KEY_URI##*/}" | sha1sum -c || exit 1'
blank

run mkdir -p rootfs/etc/apk/keys
run cp "${APK_KEY_URI##*/}" rootfs/etc/apk/keys/
run 'echo "$ALPINE_REPOS" > rootfs/etc/apk/repositories'
blank

sleep 1

say 'Now we install base system into the specified directory'
run time ./apk --root rootfs --update-cache --initdb add alpine-base
blank

say <<-EOF
	And that's it!  We have installed a fully working base Alpine system from
	packages (no prepared image) just with apk-tools.  This was very fast,
	wasn't? ;)  Even when it fetches packages from Internet through WiFi...

	And it's really very small...
EOF

sleep 2

run cd rootfs
run du -d 1 -hx .
run 'find . -xdev -type f | wc -l'
blank

say <<-EOF
	Let's try to actually chroot into it...
EOF

run cp /etc/resolv.conf etc/
run mount -v -t proc none proc
run mount -v --rbind /sys sys
run mount -v --rbind /dev dev
blank

run chroot . ps aux
blank

say <<-EOF
	And install some packages...
EOF

run chroot . apk add nginx neovim 
blank

say <<-EOF
	You may ask how is this useful.  Well, for example, you can trivially
	install Alpine on Travis CI, even with emulation of different architectures
	and build or test software.

	There's a script made specially for that:
	    https://github.com/alpinelinux/alpine-chroot-install/
EOF