#!/bin/sh
set -eu

usage() {
	cat <<-'EOF'
		Usage:
		  ifnew [-v] FILE
	EOF
}

MV_ARGS=''
while getopts 'v' flag; do
	case "$flag" in
		(v)
			MV_ARGS='-v'
			;;
		(*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))

FILE="${1:-}"
eval "$(assert-arg -- "$FILE" 'FILE')"


STDIN="$FILE.$(uuidx).tmp"
trap 'rm -f "$STDIN"' EXIT

cat - > "$STDIN"
cmp -s "$STDIN" "$FILE" || mv $MV_ARGS "$STDIN" "$FILE"