gencmdline

#!/bin/bash
#
# Generate a kernel cmdline string from /etc/cmdline and /etc/cmdline.d/

set -euo pipefail

readonly SELF="${0##*/}"

usage() {
	cat <<-EOF
		Usage: ${SELF} [OPTIONS]... [ROOT]

		Generate a kernel cmdline string from /etc/cmdline and /etc/cmdline.d/
		Optionally reads from an alternate root directory at ROOT.

		OPTIONS:
		  -h, --help        Print this help message

	EOF
	exit 0
}

error() {
	if [[ $# -gt 0 ]]; then
		>&2 echo "${SELF}: $@"
	fi
	exit 1
}

error_usage() {
	if [[ $# -gt 0 ]]; then
		>&2 echo "${SELF}: $@"
	fi
	>&2 echo "Try '${SELF} --help' for more information"
	exit 1
}

main() {
	# Read arguments
	local opts
	if ! opts="$(getopt -n "${SELF}" -o h -l help -- "$@")"; then
		error_usage
	fi
	eval set -- "${opts}"
	unset opts

	while [[ $# -gt 0 ]]; do
		case "$1" in
			-h|--help)  usage;;
			--)         shift 1; break;;
			*)          error "internal error [1]";;
		esac
	done

	if [[ $# -gt 1 ]]; then
		error_usage "invalid operands"
	fi

	# Normalize ROOT path
	local ROOT
	if ! ROOT="$(realpath -eq "${1:-/}")" || [[ ! -d "${ROOT}" ]]; then
		error "$1: No such file or directory"
	else
		readonly ROOT
	fi

	# Generate cmdline string
	# Use unquoted echo and subshell to normalize whitespace and concatenate to
	# a space delimited single line
	echo -E $(cat $ROOT/etc/cmdline $ROOT/etc/cmdline.d/* 2>/dev/null | sed 's/#.*//')
}

main "$@"

# vim: ft=sh sw=0 sts=0 noet