osi-tools/Documentation/module-examples/testuser.sh

#!/hint/bash -euE
# Copyright (C) 2018  Luke Shumaker
# SPDX-License-Identifier: AGPL-3.0-or-later

post_install+=(01:testuser:early)
testuser:early() {
	local arg_mountpoint=$1

	if ! grep -q ^testuser: -- "$arg_mountpoint/etc/passwd"; then
		arch-chroot -- "$arg_mountpoint" useradd \
		       --gid=users \
		       --comment='Test User' \
		       --create-home \
		       testuser
	fi
}

post_install+=(90:testuser:late)
testuser:late() {
	local arg_mountpoint=$1

	local uidgid
	uidgid=$(awk -v FS=: -v OFS=: '$1 == "testuser" { print $3, $4 }' < "${arg_mountpoint}/etc/passwd")
	chown -R -- "$uidgid" "${arg_mountpoint}/home/testuser"
}