add non-interactive mode: -c, script files and commands from stdin

- gosh -c 'command' runs the command and exits, so gosh works as login
  shell for ssh host command, scp and rsync
- gosh script runs a script file, lines starting with # are skipped
- without a terminal, commands are read from stdin (byte by byte, so
  started commands can read the rest of stdin)
- the exit status is the one of the last command (127 not found,
  126 not executable, 128+n killed by signal n)
- -i forces interactive mode, -l/--login is accepted

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -29,9 +29,32 @@ Features:
     disabled with $NO_COLOR, TERM=dumb or when output is not a terminal
   - Environment variable expansion ($VAR, ${VAR}, ${VAR:-default});
     using an unset variable is an error, use ${VAR:-} for an empty default
+  - Non-interactive use: gosh -c 'command', gosh script, command | gosh;
+    the exit status is the one of the last command
 
 ```
 
+### Aufruf
+
+```
+gosh [-l] [-i] [script]
+gosh [-l] -c command
+gosh -version
+```
+
+| Aufruf                 | Verhalten                                                        |
+|------------------------|------------------------------------------------------------------|
+| `gosh`                 | interaktive Shell (wenn stdin ein Terminal ist)                  |
+| `gosh -c 'befehl'`     | führt den Befehl aus und beendet sich                            |
+| `gosh skript.gosh`     | führt das Skript Zeile für Zeile aus                             |
+| `befehle \| gosh`      | liest die Befehle von stdin                                      |
+| `-i`                   | erzwingt den interaktiven Modus, auch ohne Terminal              |
+| `-l`, `--login`        | Login-Shell (wird akzeptiert, eine Startdatei gibt es noch nicht) |
+
+Ohne Terminal bricht gosh bei einem fehlgeschlagenen Befehl nicht ab und beendet sich mit dem Exit-Status des letzten Befehls: `127`, wenn ein Befehl nicht gefunden wurde, `126`, wenn er nicht ausführbar ist, `128+n`, wenn er durch Signal `n` beendet wurde. Leere Zeilen und Zeilen, die mit `#` beginnen, werden übersprungen, Skripte können also mit `#!/usr/bin/gosh` beginnen.
+
+Damit funktionieren auch `ssh host befehl`, `scp` und `rsync`, wenn gosh als Login-Shell gesetzt ist. Da gosh `;`, `&&` und Pipes noch nicht kennt, darf der Befehl dabei aber nur aus einem einfachen Kommando bestehen.
+
 ### Farben
 
 Der Prompt wird über die Umgebungsvariable `GOSH_COLORS` eingefärbt. Sie besteht aus durch `:` getrennten Einträgen `schlüssel=code`:

main.go

@@ -1,9 +1,11 @@
 package main
 
 import (
+	"bufio"
 	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"os"
 	"os/exec"
 	"os/signal"
@@ -11,6 +13,7 @@ import (
 	"path/filepath"
 	"runtime/debug"
 	"strings"
+	"syscall"
 	"unicode"
 	"unicode/utf8"
 
@@ -611,15 +614,151 @@ func completeFilePath(line, prefix string) []string {
 	return matches
 }
 
+const usage = `usage: gosh [-l] [-i] [script]
+       gosh [-l] -c command
+       gosh -version`
+
 func main() {
-	if len(os.Args) > 1 {
+	os.Exit(run(os.Args[1:]))
-		switch os.Args[1] {
+}
-		case "-version", "--version", "-V":
+
+// run parses the command line and runs gosh in the matching mode. It returns
+// the exit status of the shell.
+func run(args []string) int {
+	// -l/--login is accepted for compatibility (e.g. "su -l", login(1)), but
+	// gosh does not read a startup file yet. -i forces interactive mode even
+	// if stdin is not a terminal.
+	forceInteractive := false
+flags:
+	for len(args) > 0 {
+		switch args[0] {
+		case "-l", "--login":
+		case "-i":
+			forceInteractive = true
+		default:
+			break flags
+		}
+		args = args[1:]
+	}
+
+	if len(args) > 0 {
+		switch arg := args[0]; {
+		case arg == "-version" || arg == "--version" || arg == "-V":
 			fmt.Println("gosh", versionInfo())
-			return
+			return 0
+		case arg == "-h" || arg == "--help":
+			fmt.Println(usage)
+			return 0
+		case arg == "-c":
+			// Like sh, further arguments are allowed (they would become $0,
+			// $1, ...), but gosh has no positional parameters yet.
+			if len(args) < 2 {
+				fmt.Fprintln(os.Stderr, "gosh: -c: option requires an argument")
+				fmt.Fprintln(os.Stderr, usage)
+				return 2
+			}
+			return runScript(strings.NewReader(args[1]))
+		case strings.HasPrefix(arg, "-") && arg != "-":
+			fmt.Fprintf(os.Stderr, "gosh: %s: invalid option\n", arg)
+			fmt.Fprintln(os.Stderr, usage)
+			return 2
+		case arg == "-":
+			return runScript(os.Stdin)
+		default:
+			f, err := os.Open(arg)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, "gosh:", err)
+				return 127
+			}
+			defer f.Close()
+			return runScript(bufio.NewReader(f))
 		}
 	}
 
+	// Without a terminal (e.g. "echo ls | gosh") read the commands from stdin.
+	if !forceInteractive && !readline.IsTerminal(int(os.Stdin.Fd())) {
+		return runScript(os.Stdin)
+	}
+
+	interactive()
+	return 0
+}
+
+// runScript executes the commands from r line by line. Like sh, it does not
+// stop at a failing command and returns the exit status of the last one.
+// Empty lines and lines starting with # (e.g. a #!/usr/bin/gosh line) are
+// skipped.
+func runScript(r io.Reader) int {
+	status := 0
+	for {
+		line, err := readLine(r)
+		if trimmed := strings.TrimSpace(line); trimmed != "" && !strings.HasPrefix(trimmed, "#") {
+			cmdErr := execInput(line)
+			status = exitStatus(cmdErr)
+			// A command that ran and failed reports its own errors.
+			var exitErr *exec.ExitError
+			if cmdErr != nil && !errors.As(cmdErr, &exitErr) {
+				fmt.Fprintln(os.Stderr, "gosh:", cmdErr)
+			}
+		}
+		if err != nil {
+			if err != io.EOF {
+				fmt.Fprintln(os.Stderr, "gosh:", err)
+				return 1
+			}
+			return status
+		}
+	}
+}
+
+// readLine reads a single line from r without the trailing newline. It reads
+// byte by byte so that nothing after the line is consumed: when the script
+// comes from stdin, the commands it starts read the rest of stdin (like in
+// sh, "printf 'cat\nhello\n' | gosh" prints hello). Pass a bufio.Reader if
+// that does not matter.
+func readLine(r io.Reader) (string, error) {
+	var b strings.Builder
+	buf := make([]byte, 1)
+	for {
+		n, err := r.Read(buf)
+		if n > 0 {
+			if buf[0] == '\n' {
+				return b.String(), nil
+			}
+			b.WriteByte(buf[0])
+		}
+		if err != nil {
+			return b.String(), err
+		}
+	}
+}
+
+// exitStatus converts the result of execInput into a shell exit status: the
+// exit code of the command, 128+n if it was killed by signal n, 127 if it was
+// not found, 126 if it could not be executed and 1 for other errors.
+func exitStatus(err error) int {
+	if err == nil {
+		return 0
+	}
+	var exitErr *exec.ExitError
+	if errors.As(err, &exitErr) {
+		if ws, ok := exitErr.Sys().(syscall.WaitStatus); ok && ws.Signaled() {
+			return 128 + int(ws.Signal())
+		}
+		return exitErr.ExitCode()
+	}
+	if errors.Is(err, exec.ErrNotFound) || errors.Is(err, fs.ErrNotExist) {
+		return 127
+	}
+	if errors.Is(err, fs.ErrPermission) {
+		return 126
+	}
+	return 1
+}
+
+// interactive runs the interactive shell with line editing, history and
+// completion until the user exits.
+func interactive() {
 	// Ctrl+C sends SIGINT to the whole foreground process group. Catch it so
 	// that it only stops the running command and not the shell. (signal.Ignore
 	// would be inherited by the child processes.)
@@ -800,7 +939,9 @@ Features:
     (keys user, root, path; values are ANSI SGR codes, empty = no color);
     disabled with $NO_COLOR, TERM=dumb or when output is not a terminal
   - Environment variable expansion ($VAR, ${VAR}, ${VAR:-default});
-    using an unset variable is an error, use ${VAR:-} for an empty default`)
+    using an unset variable is an error, use ${VAR:-} for an empty default
+  - Non-interactive use: gosh -c 'command', gosh script, command | gosh;
+    the exit status is the one of the last command`)
 		return nil
 	}
 

main_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"bytes"
 	"io"
 	"os"
@@ -1173,7 +1174,7 @@ func TestShell_History(t *testing.T) {
 	histFile := filepath.Join(t.TempDir(), "gosh", "history")
 	workDir := t.TempDir()
 
-	cmd := exec.Command(bin)
+	cmd := exec.Command(bin, "-i")
 	cmd.Dir = workDir
 	cmd.Env = append(os.Environ(), "GOSH_HISTFILE="+histFile)
 	cmd.Stdin = strings.NewReader("echo first\n set SECRET=hunter2\nexit\n")
@@ -1205,7 +1206,7 @@ func TestShell_History(t *testing.T) {
 func TestShell_SIGINTKillsOnlyChild(t *testing.T) {
 	bin := buildShell(t)
 
-	cmd := exec.Command(bin)
+	cmd := exec.Command(bin, "-i")
 	// Own process group, so that we can signal it like the terminal does
 	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
 	stdin, err := cmd.StdinPipe()
@@ -1267,3 +1268,83 @@ func TestExecInput_PassesStdin(t *testing.T) {
 		t.Errorf("command read %q from stdin, want %q", got, "hello")
 	}
 }
+
+func TestExitStatus(t *testing.T) {
+	tests := []struct {
+		input string
+		want  int
+	}{
+		{"true", 0},
+		{"false", 1},
+		{`sh -c "exit 42"`, 42},
+		{`sh -c "kill -TERM \$\$"`, 128 + 15},
+		{"gosh-no-such-command", 127},
+		{"cd /gosh-no-such-dir", 127},
+	}
+	for _, tc := range tests {
+		if got := exitStatus(execInput(tc.input)); got != tc.want {
+			t.Errorf("exitStatus(execInput(%q)) = %d, want %d", tc.input, got, tc.want)
+		}
+	}
+	if got := exitStatus(errors.New("other")); got != 1 {
+		t.Errorf("exitStatus(other error) = %d, want 1", got)
+	}
+}
+
+func TestRunScript(t *testing.T) {
+	origDir, _ := os.Getwd()
+	defer os.Chdir(origDir)
+
+	dir := t.TempDir()
+	script := "#!/usr/bin/gosh\n" +
+		"# comment\n" +
+		"\n" +
+		"cd " + dir + "\n" +
+		"  # indented comment\n" +
+		"touch first\n" +
+		"false\n" +
+		"touch second" // no trailing newline
+	if got := runScript(strings.NewReader(script)); got != 0 {
+		t.Errorf("runScript() = %d, want 0", got)
+	}
+	for _, name := range []string{"first", "second"} {
+		if _, err := os.Stat(filepath.Join(dir, name)); err != nil {
+			t.Errorf("expected %s to be created: %v", name, err)
+		}
+	}
+
+	// The status of the last command is returned
+	if got := runScript(strings.NewReader("true\nsh -c 'exit 3'\n")); got != 3 {
+		t.Errorf("runScript() = %d, want 3", got)
+	}
+}
+
+func TestRun_Options(t *testing.T) {
+	tests := []struct {
+		args []string
+		want int
+	}{
+		{[]string{"-c", "true"}, 0},
+		{[]string{"-c", "false"}, 1},
+		{[]string{"-l", "-c", "sh -c 'exit 5'"}, 5},
+		{[]string{"-c"}, 2},
+		{[]string{"-x"}, 2},
+		{[]string{"/gosh/no/such/script"}, 127},
+	}
+	for _, tc := range tests {
+		if got := run(tc.args); got != tc.want {
+			t.Errorf("run(%q) = %d, want %d", tc.args, got, tc.want)
+		}
+	}
+}
+
+func TestReadLine_DoesNotReadAhead(t *testing.T) {
+	r := strings.NewReader("first\nsecond\n")
+	line, err := readLine(r)
+	if line != "first" || err != nil {
+		t.Fatalf("readLine() = %q, %v", line, err)
+	}
+	if r.Len() != len("second\n") {
+		t.Errorf("readLine() consumed more than one line, %d bytes left", r.Len())
+	}
+}