print usage info when no any argument provided

Signed-off-by: Benjamin Wang <[email protected]>

tools/rw-benchmark/plot_data.go

@@ -46,6 +46,17 @@ Additional options:
 
 // parseParams parses all the options and arguments
 func parseParams(args ...string) (legends []string, csvFiles []string, outFile string, err error) {
+	// Require at least one argument.
+	//
+	// Usually when users use a tool in the first time, they don't know how
+	// to use it, so usually they just execute the command without any
+	// arguments. So it would be better to display the usage instead of an
+	// error message in this case.
+	if len(args) == 0 {
+		fmt.Fprintln(os.Stderr, usage())
+		os.Exit(2)
+	}
+
 	var (
 		help   bool
 		legend string
@@ -395,19 +406,25 @@ func main() {
 	legends, csvFiles, outFile, err := parseParams(os.Args[1:]...)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Failed to parse the parameters: %v\n", err)
-		os.Exit(1)
+		exit()
 	}
 
 	// load data of CSV files (1 or 2 files are expected)
 	dataMap, err := loadData(csvFiles...)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Failed to load data file(s): %v\n", err)
-		os.Exit(1)
+		exit()
 	}
 
 	// render all data in one HTML page
 	if err = renderPage(legends, dataMap, outFile); err != nil {
 		fmt.Fprintf(os.Stderr, "Failed to render data to HTML page: %v\n", err)
-		os.Exit(1)
+		exit()
 	}
 }
+
+func exit() {
+	fmt.Fprintf(os.Stderr, "\n")
+	fmt.Fprintf(os.Stderr, "Run `rw-benchmark -h` to print usage info.\n")
+	os.Exit(1)
+}