motd

#!/usr/bin/env bash
# motd -- display /etc/motd only when it is updated

. lib.bash || exit

usage() {
	echo "Usage: $progname [-dq] [-o <cache-path>] [<motd-path>]"
	echo ""
	echo_opt "-d"		"show diff if cached motd exists"
	echo_opt "-o PATH"	"use a different local cache path"
	echo_opt "-q"		"do not display modification time"
	echo_opt "PATH"		"use a different motd path"
	echo ""
	echo "'motd -dq' is suitable for login scripts."
}

mtime() { perl -e 'print ((stat $ARGV[0])[9])' "$1"; }
strftime() { perl -MPOSIX -e 'print strftime $ARGV[0], localtime $ARGV[1]' "$@"; }
when() { strftime "%F %H:%M" "$(mtime "$file")"; }
copy() { mkdir -p "${2%/*}" && cp "$1" "$2" && touch -r "$1" "$2"; }

file=/etc/motd
cached=${XDG_CACHE_HOME:-$HOME/.cache}/motd-$HOSTNAME
diff=false
quiet=false

while getopts :do:q OPT; do
	case $OPT in
	d) diff=true;;
	o) cached=$OPTARG;;
	q) quiet=true;;
	*) lib:die_getopts;;
	esac
done; shift $((OPTIND-1))

file=${1:-$file}

if [ ! -f "$cached" ]; then
	# motd added (first run on this host)
	if [ -s "$file" ]; then
		cat "$file"
		$quiet || vmsg "$file added (last update $(when))"
		copy "$file" "$cached"
	elif [ -f "$file" ]; then
		$quiet || vmsg "$file is empty (last update $(when))"
		copy "$file" "$cached"
	else
		$quiet || vmsg "$file is missing"
	fi

elif [ ! -f "$file" ]; then
	# motd removed
	if $diff; then
		diff -uN "$cached" "$file"
	else
		vmsg "$file is gone"
	fi
	rm "$cached"

elif ! cmp -s "$cached" "$file"; then
	# motd updated
	if $diff; then
		diff -uN "$cached" "$file"
	else
		cat "$file"
	fi
	vmsg "$file updated (last update $(when))"
	copy "$file" "$cached"

else
	# no change
	if ! $diff; then
		$quiet || cat "$file"
	fi
	$quiet || vmsg "$file unchanged (last update $(when))"
	copy "$file" "$cached" # in case local copy is newer
fi