Add support for changing the GITHUB_ACTOR (#229)

This adds the `-a` flag when running `act` to change the username of the GITHUB_ACTOR environment variable

Co-authored-by: Casey Lee <cplee@nektos.com>

cmd/root.go

@@ -41,6 +41,7 @@ func Execute(ctx context.Context, version string) {
 	rootCmd.Flags().BoolVarP(&input.bindWorkdir, "bind", "b", false, "bind working directory to container, rather than copy")
 	rootCmd.Flags().BoolVarP(&input.forcePull, "pull", "p", false, "pull docker image(s) if already present")
 	rootCmd.Flags().StringVarP(&input.eventPath, "eventpath", "e", "", "path to event JSON file")
+	rootCmd.PersistentFlags().StringVarP(&input.actor, "actor", "a", "nektos/act", "user that triggered the event")
 	rootCmd.PersistentFlags().StringVarP(&input.workflowsPath, "workflows", "W", "./.github/workflows/", "path to workflow files")
 	rootCmd.PersistentFlags().StringVarP(&input.workdir, "directory", "C", ".", "working directory")
 	rootCmd.PersistentFlags().BoolP("verbose", "v", false, "verbose output")
@@ -156,6 +157,7 @@ func newRunCommand(ctx context.Context, input *Input) func(*cobra.Command, []str
 
 		// run the plan
 		config := &runner.Config{
+			Actor:           input.actor,
 			EventName:       eventName,
 			EventPath:       input.EventPath(),
 			ForcePull:       input.forcePull,