return errors instead of panicking

cmd/root.go

@@ -55,18 +55,18 @@ gv2adj -f <dot file> --weight-attr len
 	`,
 	// Uncomment the following line if your bare application
 	// has an action associated with it:
-	Run: parse,
+	RunE: parse,
 }
 
-func parse(cmd *cobra.Command, args []string) {
+func parse(cmd *cobra.Command, args []string) error {
 	data, err := os.ReadFile(file)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
 	ast, err := dotfmt.ParseBytes(data)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
 	first := ast.Graphs[0]
@@ -79,15 +79,16 @@ func parse(cmd *cobra.Command, args []string) {
 
 	err = dot.UnmarshalMulti(data, graph)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
 	matrix, err := orderedAdjMatrix(graph.WeightedGraph)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
 	outputMatrix(matrix)
+	return nil
 }
 
 func orderedAdjMatrix(g igraph.WeightedGraph) (*mat.Dense, error) {
@@ -149,14 +150,6 @@ func Execute() {
 }
 
 func init() {
-	// Here you will define your flags and configuration settings.
-	// Cobra supports persistent flags, which, if defined here,
-	// will be global for your application.
-
-	// rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.gv2adj.yaml)")
-
-	// Cobra also supports local flags, which will only run
-	// when this action is called directly.
 	rootCmd.Flags().StringVarP(&file, "file", "f", "", "dot file")
 	rootCmd.MarkFlagRequired("file")