add logger

script

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -eu
+
 usage() {
 	printf "Usage: %s [-h]\n" "$0"
 }
@@ -30,15 +32,40 @@ main() {
 		case "${option}" in
 			h) help; exit 0;;
 			f) FOO="$OPTARG";;
-			*) usage; exit 1;;
+			?) log -l error "$(usage)"; exit 1;;
 		esac
 	done
 
 	FOO="${FOO:-defaultValue}"
 
+	# log [-t] [-l debug|error|info] message
+
 	exit 0
 }
 
+log() {
+	LEVEL=info
+	TIME=
+
+	while getopts "tl:" option; do
+		case "${option}" in
+			l) LEVEL="$OPTARG"; shift $((OPTIND-1));;
+			t) TIME="$(printf "[%s] " "$(date +'%Y-%m-%dT%H:%m:%S.%s')")"; shift $((OPTIND-1));;
+			*) exit 1;;
+		esac
+	done
+
+	if [ -t 2 ] && [ -z "${NO_COLOR-}" ]; then
+		case "${LEVEL}" in
+			debug) COLOR="$(tput setaf 3)";;
+			error) COLOR="$(tput setaf 1)";;
+			*) COLOR="$(tput sgr0)"
+		esac
+	fi
+
+	printf "%s%s%s\n" "${COLOR:-}" "${TIME:-}" "$*" >&2
+}
+
 trap on_interrupt INT
 
 main "$@"