build_all.sh: improve usage and error handling

Usage:
 - add more information about what the script does
 - support for -h / --help flags
 - tagging of error messages with `ERROR: ` prefix

Fixes: #244

Signed-off-by: Marco Vedovati <mvedovati@suse.com>

obs-packaging/build_all.sh

@@ -18,7 +18,6 @@ source "${script_dir}/scripts/obs-pkgs.sh"
 
 PUSH=${PUSH:-""}
 LOCAL=${LOCAL:-""}
-PUSH_TO_OBS=""
 
 export BUILD_DISTROS=${BUILD_DISTROS:-xUbuntu_16.04}
 # Packaging use this variable instead of use git user value
@@ -29,17 +28,46 @@ export AUTHOR_EMAIL="${AUTHOR_EMAIL:-user@example.com}"
 usage() {
 	msg="${1:-}"
 	exit_code=$"${2:-0}"
+	if [ -n "${msg}" ]; then
+		local logPrefix=""
+		[ ${exit_code} != "0" ] && logPrefix="ERROR: "
+		echo -e "${logPrefix}${msg}\n"
+	fi
+
 	cat <<EOT
-${msg}
 Usage:
-${script_name} <kata-branch>
+${script_name} [-h | --help] <kata-branch> [PROJ1 PROJ2 ... ]
+
+Generate OBS packages sources for the kata projects, based on branch
+kata-branch.
+${script_name} processes all the kata projects by default; alternatively you can
+specify a subset of the projects as additional arguments.
+
+Environment variables:
+PUSH        When set, push the packages sources to the openSUSE build
+            service.
+
+LOCAL       When set, build the packages locally.
+
 EOT
 	exit "${exit_code}"
 }
 
 main() {
-	local branch="${1:-}"
-	[ -n "${branch}" ] || usage "missing branch" "1"
+	case "${1:-}" in
+		"-h"|"--help")
+			usage "" "0"
+			;;
+		-*)
+			usage "Invalid option: ${1:-}" "1"
+			;;
+		"")
+			usage "missing branch" "1"
+			;;
+		*)
+			branch="${1:-}"
+			;;
+	esac
 
 	shift
 	local projectsList=("$@")