update README doc with some usage + exit prog when no file found

README.md

@@ -15,3 +15,25 @@ git clone https://gitea.thegux.fr/rmanach/packer
 ```bash
 make build
 ```
+
+## Usage
+
+### Arguments
+* **-r** (**required**) : filename regex
+* **-o** (**required**) : full path of the zip archive output
+* **-d** (**optional**) : full path of the directory to check
+* **-x** (**optional**) : remove original files after successful zip
+
+```bash
+# template usage
+./packer -r <regex> -o <output_path>
+
+# zip '.log' files located in '/root/logs' directory
+# 'root_log.zip' will be created in the current directory
+./packer -r ^.*\.log$ -d /root/logs -o root_logs.zip
+
+# zip '.doc' files located in the current directory
+# the zip archive will be create in '/home/tutu/doc/'
+# all '.doc' files will be removed after successful zip
+./packer -r ^.*\.doc$ -o /home/tutu/doc/root_log.zip -x
+```

main.go

@@ -190,8 +190,13 @@ func main() {
 	log.Printf("looking for file '%s' in '%s' ...", rd.String(), directory)
 	files, err := getFilesFromDirectoryPath(directory, rd)
 
-	// generating zip archive
 	log.Printf("files found : %d", len(files))
+	if len(files) == 0 {
+		message := fmt.Sprintf("no file found in the directory : %s with the regex : %s", directory, regex)
+		log.Fatal(message)
+	}
+
+	// generating zip archive
 	err = generateZip(outputPath, files)
 
 	// check if errors occured during zip