fix(sh): pass -h, --help to the script (#64)

We want to prioritise printing the script's own help message over the
shell's help message. Therefore, modify `rbmk sh` to only print its own
help when the script is named `-h` or `--help` and otherwise pass
arguments to the script.

pkg/cli/sh/README.md

@@ -13,6 +13,9 @@ Run `SCRIPT` using a POSIX-compliant shell interpreter providing
 to the script the given `ARGUMENTS`, which will be available to
 the script as `$1`, `$2`, etc.
 
+As a special case, if `SCRIPT` is `-h` or `--help`, the command
+prints this help message and exits.
+
 This shell implementation (based on `mvdan.cc/sh/v3`) is consistent
 across operating systems and supports:
 
@@ -111,6 +114,9 @@ using `rbmk sh $script` precisely because of this issue.
 
 ## History
 
+Since RBMK v0.12.0, the `-h, --help` flag is passed by default to the
+`SCRIPT` rather than printing the `rbmk sh` command's help.
+
 Since RBMK v0.10.0, it is possible to pass arguments to the script
 executed by `rbmk sh` using the command line.
 

pkg/cli/sh/sh.go

@@ -33,19 +33,19 @@ func (cmd command) Help(env cliutils.Environment, argv ...string) error {
 }
 
 func (cmd command) Main(ctx context.Context, env cliutils.Environment, argv ...string) error {
-	// 1. Honour requests for printing the help.
-	if cliutils.HelpRequested(argv...) {
-		return cmd.Help(env, argv...)
-	}
-
-	// 2. Ensure we have exactly one script to run.
+	// 1. Ensure we have exactly one script to run.
 	if len(argv) < 2 {
 		err := errors.New("expected a script with optional arguments")
 		fmt.Fprintf(env.Stderr(), "rbmk sh: %s\n", err.Error())
 		fmt.Fprintf(env.Stderr(), "Run `rbmk sh --help` for usage.\n")
 		return err
 	}
 
+	// 2. If the script is named `-h` or `--help` print help.
+	if argv[1] == "-h" || argv[1] == "--help" {
+		return cmd.Help(env, argv...)
+	}
+
 	// 3. Open and parse the shell script.
 	scriptPath := argv[1]
 	filep, err := env.FS().Open(scriptPath)
@@ -66,12 +66,14 @@ func (cmd command) Main(ctx context.Context, env cliutils.Environment, argv ...s
 	// scripts written before the release of RBMK v0.7.0.
 	os.Setenv("RBMK_EXE", "rbmk")
 
-	// 5. Create the shell interpreter.
+	// 5. Create the shell interpreter ensuring we properly use `--` to
+	// ensure options get passed to the script itself.
+	scriptParams := append([]string{"--"}, argv[2:]...)
 	runner, err := interp.New(
 		interp.StdIO(env.Stdin(), env.Stdout(), env.Stderr()),
 		interp.Env(expand.FuncEnviron(os.Getenv)),
 		interp.ExecHandlers(newBuiltInMiddleware()),
-		interp.Params(argv[2:]...),
+		interp.Params(scriptParams...),
 	)
 	if err != nil {
 		fmt.Fprintf(env.Stderr(), "rbmk sh: cannot create interpreter: %s\n", err.Error())