Add control flow, I/O redirection, functions, coreutils, history/completion

- I/O redirection: >, >>, <, 2>, 2>&1, &>
- Job control: background & operator
- if/elif/else/fi, for/do/done, while/until loops
- Shell functions with local/declare, positional param save/restore
- Exit code propagation via exitCodeErr sentinel
- Arithmetic expansion $((expr)) with bare variable names
- Command substitution $(cmd) with pipeline support
- Glob expansion, tilde expansion, ${VAR:-default} and other forms
- Tab completion and command history via chzyer/readline
- Inline comment stripping (# outside quotes)
- Builtins: test/[, read, printf, tr, sed, cut, tail, tee, xargs,
  basename, dirname, date, sleep, uniq, sort, wc, head, grep, find,
  true, false, break, continue, return, shift, set, unset, export,
  declare/local, source, alias, jobs, command, which, env
- Bug fixes: tokenizer parenDepth double-count for $((,
  splitPipe not paren-aware (broke pipelines in $()),
  local/declare TrimLeft stripping valid var name chars,
  parseBlocks missing nested keywords after do/then/else

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/bash/main.go

@@ -1,10 +1,13 @@
 package bash
 
 import (
-    "bufio"
 	"fmt"
 	"os"
+	"path/filepath"
 	"strings"
+
+	"github.com/chzyer/readline"
+
 	"github.com/cametendo/bash-for-windows/internal/shell"
 )
 
@@ -12,51 +15,109 @@ func Run() error {
 	args := os.Args[1:]
 
 	if len(args) > 0 {
-        if args[0] == "-c" && len(args) > 1 {
-            // Execute a command string
-            return runCommand(strings.Join(args[1:], " "))
+		switch args[0] {
+		case "-c":
+			if len(args) < 2 {
+				return fmt.Errorf("-c: option requires an argument")
+			}
+			sh := shell.New()
+			if len(args) > 2 {
+				sh.SetArgs(args[2:])
+			}
+			return sh.Execute(strings.Join(args[1:], " "))
+		case "--version":
+			fmt.Println("bash-for-windows 2.0.0 (Go-based)")
+			fmt.Println("Provides bash-compatible shell for Windows.")
+			return nil
+		default:
+			return runFile(args[0], args[1:])
 		}
-        // Run a script file
-        return runFile(args[0])
 	}
 
 	return interactive()
 }
 
-func runCommand(cmd string) error {
-    sh := shell.New()
-    return sh.Execute(cmd)
-}
-
-func runFile(path string) error {
+func runFile(path string, args []string) error {
 	data, err := os.ReadFile(path)
 	if err != nil {
 		return fmt.Errorf("%s: %v", path, err)
 	}
 	sh := shell.New()
+	sh.SetArgs(append([]string{path}, args...))
+	sh.SetVar("0", path)
 	return sh.Execute(string(data))
 }
 
+func historyFile() string {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return ""
+	}
+	// On Windows this lands in %USERPROFILE%\.bash_history
+	return filepath.Join(home, ".bash_history")
+}
+
 func interactive() error {
 	sh := shell.New()
-    reader := bufio.NewReader(os.Stdin)
 
-    fmt.Println("bash-for-windows v1.0.0")
+	// Build completer
+	completer := readline.NewPrefixCompleter(
+		readline.PcItemDynamic(func(line string) []string {
+			return dynamicComplete(sh, line)
+		}),
+	)
+
+	rl, err := readline.NewEx(&readline.Config{
+		HistoryFile:            historyFile(),
+		AutoComplete:           completer,
+		InterruptPrompt:        "^C",
+		EOFPrompt:              "exit",
+		HistorySearchFold:      true,
+		FuncFilterInputRune:    filterInput,
+	})
+	if err != nil {
+		// Fall back to dumb interactive mode
+		return interactiveDumb(sh)
+	}
+	defer rl.Close()
+
+	fmt.Fprintln(os.Stdout, "bash-for-windows v2.0.0  (type 'exit' or Ctrl+D to quit)")
+
+	var multiLine strings.Builder
 
 	for {
-        fmt.Print("bash$ ")
-        input, err := reader.ReadString('\n')
-        if err != nil {
-            break
+		prompt := buildPrompt(sh)
+		if multiLine.Len() > 0 {
+			prompt = "> "
 		}
+		rl.SetPrompt(prompt)
+
+		line, err := rl.Readline()
+		if err != nil {
+			if err.Error() == "Interrupt" {
+				// Ctrl+C: abort current multi-line input
+				multiLine.Reset()
+				fmt.Fprintln(os.Stdout)
+				continue
+			}
+			break // EOF
+		}
+
+		if multiLine.Len() > 0 {
+			multiLine.WriteString("\n")
+		}
+		multiLine.WriteString(line)
+
+		input := multiLine.String()
+		if shell.IsIncomplete(input) {
+			continue // wait for more input
+		}
+		multiLine.Reset()
 
 		input = strings.TrimSpace(input)
 		if input == "" {
 			continue
 		}
-        if input == "exit" {
-            break
-        }
 
 		if err := sh.Execute(input); err != nil {
 			fmt.Fprintf(os.Stderr, "bash: %v\n", err)
@@ -64,3 +125,137 @@ func interactive() error {
 	}
 	return nil
 }
+
+// interactiveDumb is a fallback that doesn't need readline.
+func interactiveDumb(sh *shell.Shell) error {
+	fmt.Fprintln(os.Stdout, "bash-for-windows v2.0.0")
+
+	var multiLine strings.Builder
+	buf := make([]byte, 4096)
+
+	for {
+		prompt := buildPrompt(sh)
+		if multiLine.Len() > 0 {
+			prompt = "> "
+		}
+		fmt.Fprint(os.Stdout, prompt)
+
+		n, err := os.Stdin.Read(buf)
+		if n > 0 {
+			chunk := string(buf[:n])
+			if multiLine.Len() > 0 {
+				multiLine.WriteString("\n")
+			}
+			multiLine.WriteString(strings.TrimRight(chunk, "\r\n"))
+
+			input := multiLine.String()
+			if shell.IsIncomplete(input) {
+				continue
+			}
+			multiLine.Reset()
+			input = strings.TrimSpace(input)
+			if input == "" {
+				continue
+			}
+			if execErr := sh.Execute(input); execErr != nil {
+				fmt.Fprintf(os.Stderr, "bash: %v\n", execErr)
+			}
+		}
+		if err != nil {
+			break
+		}
+	}
+	return nil
+}
+
+func buildPrompt(sh *shell.Shell) string {
+	pwd, _ := os.Getwd()
+	home, _ := os.UserHomeDir()
+	if home != "" && strings.HasPrefix(pwd, home) {
+		pwd = "~" + pwd[len(home):]
+	}
+	// Show exit code in prompt if non-zero
+	exitCode := sh.GetVar("?")
+	suffix := "$ "
+	if exitCode != "0" && exitCode != "" {
+		suffix = "[" + exitCode + "]$ "
+	}
+	return pwd + suffix
+}
+
+// dynamicComplete provides tab completion for commands and paths.
+func dynamicComplete(sh *shell.Shell, line string) []string {
+	line = strings.TrimLeft(line, " \t")
+	var completions []string
+
+	// Check if we're completing the first word (command) or an argument (path)
+	words := strings.Fields(line)
+	completingCommand := len(words) == 0 || (len(words) == 1 && !strings.HasSuffix(line, " "))
+
+	if completingCommand {
+		prefix := ""
+		if len(words) == 1 {
+			prefix = words[0]
+		}
+		// Builtin/function names — access via the shell instance
+		// (we can't iterate unexported fields, so use a public method)
+		for _, name := range sh.BuiltinNames() {
+			if strings.HasPrefix(name, prefix) {
+				completions = append(completions, name)
+			}
+		}
+		// PATH executables
+		for _, dir := range filepath.SplitList(os.Getenv("PATH")) {
+			entries, err := os.ReadDir(dir)
+			if err != nil {
+				continue
+			}
+			for _, e := range entries {
+				name := e.Name()
+				// Strip .exe on completion display
+				name = strings.TrimSuffix(name, ".exe")
+				if strings.HasPrefix(name, prefix) {
+					completions = append(completions, name)
+				}
+			}
+		}
+	} else {
+		// Path completion
+		prefix := ""
+		if len(words) > 0 {
+			prefix = words[len(words)-1]
+			if strings.HasSuffix(line, " ") {
+				prefix = ""
+			}
+		}
+		dir := filepath.Dir(prefix)
+		base := filepath.Base(prefix)
+		if prefix == "" || strings.HasSuffix(prefix, "/") || strings.HasSuffix(prefix, "\\") {
+			dir = prefix
+			base = ""
+		}
+		entries, err := os.ReadDir(dir)
+		if err == nil {
+			for _, e := range entries {
+				name := e.Name()
+				if strings.HasPrefix(name, base) {
+					p := filepath.Join(dir, name)
+					if e.IsDir() {
+						p += "/"
+					}
+					completions = append(completions, p)
+				}
+			}
+		}
+	}
+
+	return completions
+}
+
+func filterInput(r rune) (rune, bool) {
+	// Block Ctrl+Z (26) — on Windows this would suspend; we handle it gracefully
+	if r == 26 {
+		return r, false
+	}
+	return r, true
+}

go.mod

@@ -1,3 +1,8 @@
 module github.com/cametendo/bash-for-windows
 
 go 1.26.2
+
+require (
+	github.com/chzyer/readline v1.5.1 // indirect
+	golang.org/x/sys v0.0.0-20220310020820-b874c991c1a5 // indirect
+)

go.sum

@@ -0,0 +1,6 @@
+github.com/chzyer/logex v1.2.1/go.mod h1:JLbx6lG2kDbNRFnfkgvh4eRJRPX1QCoOIWomwysCBrQ=
+github.com/chzyer/readline v1.5.1 h1:upd/6fQk4src78LMRzh5vItIt361/o4uq553V8B5sGI=
+github.com/chzyer/readline v1.5.1/go.mod h1:Eh+b79XXUwfKfcPLepksvw2tcLE/Ct21YObkaSkeBlk=
+github.com/chzyer/test v1.0.0/go.mod h1:2JlltgoNkt4TW/z9V/IzDdFaMTM2JPIi26O1pF38GC8=
+golang.org/x/sys v0.0.0-20220310020820-b874c991c1a5 h1:y/woIyUBFbpQGKS0u1aHF/40WUDnek3fPOyD08H5Vng=
+golang.org/x/sys v0.0.0-20220310020820-b874c991c1a5/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

internal/shell/control.go

@@ -0,0 +1,352 @@
+package shell
+
+import (
+	"fmt"
+	"strings"
+)
+
+// executeIf handles: if COND; then BODY; [elif COND; then BODY;]* [else BODY;] fi
+func (s *Shell) executeIf(block string) error {
+	stmts := splitStatements(block)
+
+	type branch struct {
+		cond []string
+		body []string
+	}
+
+	var branches []branch
+	var elseBody []string
+
+	phase := "if_cond"
+	var curCond []string
+	var curBody []string
+
+	for _, stmt := range stmts {
+		w := firstWord(stmt)
+		rest := afterWord(stmt)
+
+		switch {
+		case w == "if" && phase == "if_cond":
+			if rest != "" {
+				curCond = append(curCond, rest)
+			}
+		case w == "then":
+			if rest != "" {
+				curBody = append(curBody, rest)
+			}
+			phase = "body"
+		case w == "elif":
+			branches = append(branches, branch{curCond, curBody})
+			curCond = nil
+			curBody = nil
+			if rest != "" {
+				curCond = append(curCond, rest)
+			}
+			phase = "elif_cond"
+		case w == "else":
+			branches = append(branches, branch{curCond, curBody})
+			curCond = nil
+			curBody = nil
+			if rest != "" {
+				elseBody = append(elseBody, rest)
+			}
+			phase = "else"
+		case w == "fi":
+			switch phase {
+			case "body":
+				branches = append(branches, branch{curCond, curBody})
+			case "else":
+				if rest != "" {
+					elseBody = append(elseBody, rest)
+				}
+			}
+		default:
+			switch phase {
+			case "if_cond", "elif_cond":
+				curCond = append(curCond, stmt)
+			case "body":
+				curBody = append(curBody, stmt)
+			case "else":
+				elseBody = append(elseBody, stmt)
+			}
+		}
+	}
+
+	for _, b := range branches {
+		cond := strings.Join(b.cond, "\n")
+		s.Execute(cond) //nolint — we only care about $?
+		if s.vars["?"] == "0" {
+			return s.Execute(strings.Join(b.body, "\n"))
+		}
+	}
+	if len(elseBody) > 0 {
+		return s.Execute(strings.Join(elseBody, "\n"))
+	}
+	return nil
+}
+
+// executeFor handles: for VAR in WORDS; do BODY; done
+// (also: for VAR; do BODY; done — iterates positional params)
+func (s *Shell) executeFor(block string) error {
+	stmts := splitStatements(block)
+	if len(stmts) == 0 {
+		return nil
+	}
+
+	// Parse "for VAR in WORDS"
+	header := stmts[0]
+	fields := strings.Fields(header)
+	if len(fields) < 2 {
+		return fmt.Errorf("for: bad syntax")
+	}
+	varName := fields[1]
+
+	var items []string
+	inIdx := -1
+	for i, w := range fields {
+		if w == "in" {
+			inIdx = i
+			break
+		}
+	}
+	if inIdx >= 0 {
+		for _, raw := range fields[inIdx+1:] {
+			expanded := s.expandWord(raw)
+			items = append(items, s.expandGlob(expanded)...)
+		}
+	} else {
+		// for var; do ... → iterate positional params
+		items = s.args
+	}
+
+	// Collect body between "do" and "done"
+	var bodyStmts []string
+	inBody := false
+	for _, stmt := range stmts[1:] {
+		w := firstWord(stmt)
+		if !inBody {
+			if w == "do" {
+				inBody = true
+				if rest := afterWord(stmt); rest != "" {
+					bodyStmts = append(bodyStmts, rest)
+				}
+			}
+			continue
+		}
+		if w == "done" {
+			break
+		}
+		bodyStmts = append(bodyStmts, stmt)
+	}
+
+	body := strings.Join(bodyStmts, "\n")
+
+	for _, item := range items {
+		s.vars[varName] = item
+		if err := s.Execute(body); err != nil {
+			if be, ok := err.(breakErr); ok {
+				if be.n <= 1 {
+					break
+				}
+				return breakErr{be.n - 1}
+			}
+			if ce, ok := err.(continueErr); ok {
+				if ce.n <= 1 {
+					continue
+				}
+				return continueErr{ce.n - 1}
+			}
+			if _, ok := err.(returnErr); ok {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// executeWhileUntil handles while/until loops.
+func (s *Shell) executeWhileUntil(block string, isUntil bool) error {
+	stmts := splitStatements(block)
+	if len(stmts) == 0 {
+		return nil
+	}
+
+	// Parse condition (everything from "while/until COND" up to "do")
+	var condStmts []string
+	if rest := afterWord(stmts[0]); rest != "" {
+		condStmts = append(condStmts, rest)
+	}
+
+	var bodyStmts []string
+	inBody := false
+	for _, stmt := range stmts[1:] {
+		w := firstWord(stmt)
+		if !inBody {
+			if w == "do" {
+				inBody = true
+				if rest := afterWord(stmt); rest != "" {
+					bodyStmts = append(bodyStmts, rest)
+				}
+			} else {
+				condStmts = append(condStmts, stmt)
+			}
+			continue
+		}
+		if w == "done" {
+			break
+		}
+		bodyStmts = append(bodyStmts, stmt)
+	}
+
+	cond := strings.Join(condStmts, "\n")
+	body := strings.Join(bodyStmts, "\n")
+
+	for {
+		s.Execute(cond) //nolint
+		condOk := s.vars["?"] == "0"
+
+		if (isUntil && condOk) || (!isUntil && !condOk) {
+			break
+		}
+
+		if err := s.Execute(body); err != nil {
+			if be, ok := err.(breakErr); ok {
+				if be.n <= 1 {
+					break
+				}
+				return breakErr{be.n - 1}
+			}
+			if ce, ok := err.(continueErr); ok {
+				if ce.n <= 1 {
+					continue
+				}
+				return continueErr{ce.n - 1}
+			}
+			if _, ok := err.(returnErr); ok {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// defineFunction parses and registers a shell function definition.
+func (s *Shell) defineFunction(block string) error {
+	stmts := splitStatements(block)
+	if len(stmts) == 0 {
+		return fmt.Errorf("syntax error: empty function")
+	}
+
+	first := stmts[0]
+	var name string
+
+	if strings.HasPrefix(first, "function ") {
+		rest := strings.TrimPrefix(first, "function ")
+		rest = strings.TrimSpace(rest)
+		// Strip trailing () and {
+		rest = strings.TrimSuffix(strings.TrimSpace(rest), "{")
+		rest = strings.TrimSuffix(strings.TrimSpace(rest), "()")
+		name = strings.TrimSpace(rest)
+	} else {
+		parenIdx := strings.Index(first, "(")
+		if parenIdx < 0 {
+			return fmt.Errorf("syntax error: bad function definition")
+		}
+		name = strings.TrimSpace(first[:parenIdx])
+	}
+
+	if !isValidIdentifier(name) {
+		return fmt.Errorf("syntax error: invalid function name %q", name)
+	}
+
+	// Find the opening { in the block — it may be on the same line as the name
+	// or on a following stmt.  Everything after { (up to closing }) is the body.
+	var bodyStmts []string
+	inBody := false
+
+	for _, stmt := range stmts {
+		trimmed := strings.TrimSpace(stmt)
+
+		if !inBody {
+			// Look for { in this stmt
+			braceIdx := strings.Index(trimmed, "{")
+			if braceIdx >= 0 {
+				inBody = true
+				rest := strings.TrimSpace(trimmed[braceIdx+1:])
+				if rest != "" && rest != "}" {
+					bodyStmts = append(bodyStmts, rest)
+				}
+				// Check if } is also on this line (single-liner like name() { cmd; })
+				if strings.HasSuffix(trimmed, "}") && braceIdx < len(trimmed)-1 {
+					// body is between { and }
+					inner := strings.TrimSpace(trimmed[braceIdx+1 : len(trimmed)-1])
+					bodyStmts = nil
+					if inner != "" {
+						bodyStmts = append(bodyStmts, inner)
+					}
+					break
+				}
+			}
+			continue
+		}
+
+		if trimmed == "}" {
+			break
+		}
+		bodyStmts = append(bodyStmts, stmt)
+	}
+
+	funcBody := strings.Join(bodyStmts, "\n")
+	s.funcs[name] = funcBody
+
+	funcName := name
+	s.builtins[funcName] = func(args []string) error {
+		return s.callFunction(funcName, args)
+	}
+	return nil
+}
+
+func (s *Shell) callFunction(name string, args []string) error {
+	body, ok := s.funcs[name]
+	if !ok {
+		return fmt.Errorf("%s: function not found", name)
+	}
+
+	// Save positional params and exit code
+	oldArgs := s.args
+	savedPos := map[string]string{}
+	for k, v := range s.vars {
+		if k == "#" || k == "@" || k == "*" || (len(k) == 1 && k[0] >= '1' && k[0] <= '9') {
+			savedPos[k] = v
+		}
+	}
+
+	s.SetArgs(args)
+	s.vars["?"] = "0" // reset before running body
+
+	err := s.Execute(body)
+
+	// Capture the function's exit code BEFORE restoring params (which might not include ?)
+	funcExitCode := s.lastExit
+
+	// Restore positional params
+	s.args = oldArgs
+	for k, v := range savedPos {
+		s.vars[k] = v
+	}
+
+	if re, ok := err.(returnErr); ok {
+		if re.code != 0 {
+			return exitCodeErr{re.code}
+		}
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	// Propagate last command's exit code from the function body
+	if funcExitCode != 0 {
+		return exitCodeErr{funcExitCode}
+	}
+	return nil
+}

internal/shell/exec.go

@@ -0,0 +1,375 @@
+package shell
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+type redirect struct {
+	fd   int    // 0=stdin 1=stdout 2=stderr -1=both stdout+stderr
+	mode string // ">" ">>" "<"
+	dest string // filename or "&1" "&2"
+}
+
+// executePipeline handles background jobs (&) and pipelines (|).
+func (s *Shell) executePipeline(input string) error {
+	input = strings.TrimSpace(input)
+	if input == "" {
+		return nil
+	}
+
+	// Background job: trailing & (not &&)
+	bg := false
+	if strings.HasSuffix(input, "&") && !strings.HasSuffix(input, "&&") {
+		bg = true
+		input = strings.TrimSuffix(strings.TrimSuffix(input, "&"), " ")
+	}
+
+	parts := splitPipe(input)
+	if len(parts) == 1 {
+		if bg {
+			return s.executeCommandBg(strings.TrimSpace(parts[0]))
+		}
+		return s.executeCommand(strings.TrimSpace(parts[0]))
+	}
+	return s.doPipe(parts, bg)
+}
+
+// splitPipe splits by | but not ||, respecting quotes.
+func splitPipe(input string) []string {
+	var parts []string
+	current := strings.Builder{}
+	inSingle := false
+	inDouble := false
+	parenDepth := 0
+	pendingDollar := false
+
+	for i := 0; i < len(input); i++ {
+		c := input[i]
+		switch {
+		case c == '\'' && !inDouble && parenDepth == 0:
+			inSingle = !inSingle
+			current.WriteByte(c)
+		case c == '"' && !inSingle && parenDepth == 0:
+			inDouble = !inDouble
+			current.WriteByte(c)
+		case c == '$' && !inSingle && !inDouble && i+1 < len(input) && input[i+1] == '(':
+			pendingDollar = true
+			current.WriteByte(c)
+		case c == '(' && !inSingle && !inDouble && (parenDepth > 0 || pendingDollar):
+			parenDepth++
+			pendingDollar = false
+			current.WriteByte(c)
+		case c == ')' && !inSingle && !inDouble && parenDepth > 0:
+			parenDepth--
+			current.WriteByte(c)
+		case c == '|' && !inSingle && !inDouble && parenDepth == 0:
+			if i+1 < len(input) && input[i+1] == '|' {
+				current.WriteByte(c) // part of ||, pass through
+			} else {
+				parts = append(parts, strings.TrimSpace(current.String()))
+				current.Reset()
+				pendingDollar = false
+			}
+		default:
+			pendingDollar = false
+			current.WriteByte(c)
+		}
+	}
+	if current.Len() > 0 {
+		parts = append(parts, strings.TrimSpace(current.String()))
+	}
+	return parts
+}
+
+// executeCommand executes a single command (no pipes, no &&/||).
+func (s *Shell) executeCommand(input string) error {
+	input = strings.TrimSpace(input)
+	if input == "" {
+		return nil
+	}
+
+	tokens := s.tokenize(input)
+	if len(tokens) == 0 {
+		return nil
+	}
+
+	cmdArgs, redirects := extractRedirects(tokens)
+	if len(cmdArgs) == 0 {
+		// Pure redirection, e.g. "> file" creates/truncates file
+		return s.withRedirects(redirects, func() error { return nil })
+	}
+
+	cmdName := cmdArgs[0]
+	args := cmdArgs[1:]
+
+	// Alias expansion
+	if alias, ok := aliases[cmdName]; ok {
+		full := alias
+		if len(args) > 0 {
+			full += " " + strings.Join(args, " ")
+		}
+		return s.withRedirects(redirects, func() error {
+			return s.Execute(full)
+		})
+	}
+
+	// Builtin
+	if builtin, ok := s.builtins[cmdName]; ok {
+		return s.withRedirects(redirects, func() error {
+			return builtin(args)
+		})
+	}
+
+	// External
+	return s.withRedirects(redirects, func() error {
+		return s.executeExternal(cmdName, args)
+	})
+}
+
+func extractRedirects(tokens []string) ([]string, []redirect) {
+	var args []string
+	var redirects []redirect
+
+	i := 0
+	for i < len(tokens) {
+		tok := tokens[i]
+
+		switch {
+		// 2>&1
+		case tok == "2>&1":
+			redirects = append(redirects, redirect{2, ">", "&1"})
+			i++
+		// 1>&2
+		case tok == "1>&2":
+			redirects = append(redirects, redirect{1, ">", "&2"})
+			i++
+		// &> or &>> (both stdout+stderr)
+		case tok == "&>" || tok == "&>>":
+			if i+1 < len(tokens) {
+				redirects = append(redirects, redirect{-1, strings.TrimPrefix(tok, "&"), tokens[i+1]})
+				i += 2
+			} else {
+				i++
+			}
+		case strings.HasPrefix(tok, "&>"):
+			mode := ">"
+			dest := tok[2:]
+			if strings.HasPrefix(dest, ">") {
+				mode = ">>"
+				dest = dest[1:]
+			}
+			redirects = append(redirects, redirect{-1, mode, dest})
+			i++
+		// 2> 2>> 2>file
+		case tok == "2>" || tok == "2>>":
+			if i+1 < len(tokens) {
+				redirects = append(redirects, redirect{2, tok[1:], tokens[i+1]})
+				i += 2
+			} else {
+				i++
+			}
+		case strings.HasPrefix(tok, "2>>"):
+			redirects = append(redirects, redirect{2, ">>", tok[3:]})
+			i++
+		case strings.HasPrefix(tok, "2>"):
+			redirects = append(redirects, redirect{2, ">", tok[2:]})
+			i++
+		// > >>
+		case tok == ">" || tok == ">>":
+			if i+1 < len(tokens) {
+				redirects = append(redirects, redirect{1, tok, tokens[i+1]})
+				i += 2
+			} else {
+				i++
+			}
+		case strings.HasPrefix(tok, ">>") && len(tok) > 2:
+			redirects = append(redirects, redirect{1, ">>", tok[2:]})
+			i++
+		case strings.HasPrefix(tok, ">") && len(tok) > 1:
+			redirects = append(redirects, redirect{1, ">", tok[1:]})
+			i++
+		// < (stdin)
+		case tok == "<":
+			if i+1 < len(tokens) {
+				redirects = append(redirects, redirect{0, "<", tokens[i+1]})
+				i += 2
+			} else {
+				i++
+			}
+		case strings.HasPrefix(tok, "<") && len(tok) > 1 && tok[1] != '<':
+			redirects = append(redirects, redirect{0, "<", tok[1:]})
+			i++
+		default:
+			args = append(args, tok)
+			i++
+		}
+	}
+	return args, redirects
+}
+
+func (s *Shell) withRedirects(redirects []redirect, fn func() error) error {
+	if len(redirects) == 0 {
+		return fn()
+	}
+
+	oldIn, oldOut, oldErr := s.Stdin, s.Stdout, s.Stderr
+	var toClose []io.Closer
+
+	defer func() {
+		s.Stdin, s.Stdout, s.Stderr = oldIn, oldOut, oldErr
+		for _, c := range toClose {
+			c.Close()
+		}
+	}()
+
+	for _, r := range redirects {
+		switch r.mode {
+		case ">":
+			if r.dest == "&1" {
+				s.Stderr = s.Stdout
+			} else if r.dest == "&2" {
+				s.Stdout = s.Stderr
+			} else {
+				f, err := os.Create(r.dest)
+				if err != nil {
+					return fmt.Errorf("cannot open %s: %v", r.dest, err)
+				}
+				toClose = append(toClose, f)
+				if r.fd == 1 || r.fd == -1 {
+					s.Stdout = f
+				}
+				if r.fd == 2 || r.fd == -1 {
+					s.Stderr = f
+				}
+			}
+		case ">>":
+			f, err := os.OpenFile(r.dest, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+			if err != nil {
+				return fmt.Errorf("cannot open %s: %v", r.dest, err)
+			}
+			toClose = append(toClose, f)
+			if r.fd == 1 || r.fd == -1 {
+				s.Stdout = f
+			}
+			if r.fd == 2 || r.fd == -1 {
+				s.Stderr = f
+			}
+		case "<":
+			f, err := os.Open(r.dest)
+			if err != nil {
+				return fmt.Errorf("cannot open %s: %v", r.dest, err)
+			}
+			toClose = append(toClose, f)
+			s.Stdin = f
+		}
+	}
+	return fn()
+}
+
+func (s *Shell) executeExternal(cmdName string, args []string) error {
+	path := findExecutable(cmdName)
+	if path == "" {
+		fmt.Fprintf(s.Stderr, "%s: command not found\n", cmdName)
+		return exitCodeErr{127}
+	}
+	cmd := exec.Command(path, args...)
+	cmd.Stdin = s.Stdin
+	cmd.Stdout = s.Stdout
+	cmd.Stderr = s.Stderr
+	err := cmd.Run()
+	if err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			return exitCodeErr{exitErr.ExitCode()}
+		}
+	}
+	return err
+}
+
+func (s *Shell) executeCommandBg(input string) error {
+	tokens := s.tokenize(input)
+	if len(tokens) == 0 {
+		return nil
+	}
+	cmdArgs, _ := extractRedirects(tokens)
+	if len(cmdArgs) == 0 {
+		return nil
+	}
+	path := findExecutable(cmdArgs[0])
+	if path == "" {
+		return fmt.Errorf("%s: command not found", cmdArgs[0])
+	}
+	cmd := exec.Command(path, cmdArgs[1:]...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Start(); err != nil {
+		return err
+	}
+	pid := cmd.Process.Pid
+	s.vars["!"] = fmt.Sprintf("%d", pid)
+	fmt.Fprintf(s.Stderr, "[1] %d\n", pid)
+	go func() { cmd.Wait() }()
+	return nil
+}
+
+func findExecutable(name string) string {
+	// Direct path
+	if strings.ContainsAny(name, "/\\") {
+		if info, err := os.Stat(name); err == nil && !info.IsDir() {
+			abs, _ := filepath.Abs(name)
+			return abs
+		}
+		return ""
+	}
+	path := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(path) {
+		for _, candidate := range []string{
+			filepath.Join(dir, name),
+			filepath.Join(dir, name+".exe"),
+			filepath.Join(dir, name+".cmd"),
+			filepath.Join(dir, name+".bat"),
+		} {
+			if info, err := os.Stat(candidate); err == nil && !info.IsDir() {
+				return candidate
+			}
+		}
+	}
+	return ""
+}
+
+// doPipe executes a pipeline where each stage feeds into the next.
+func (s *Shell) doPipe(commands []string, bg bool) error {
+	_ = bg // background pipe support would require goroutines; skip for now
+
+	var prevBuf []byte
+
+	for i, cmd := range commands {
+		isLast := i == len(commands)-1
+		var stdinReader io.Reader
+
+		if i == 0 {
+			stdinReader = s.Stdin
+		} else {
+			stdinReader = bytes.NewReader(prevBuf)
+		}
+
+		if isLast {
+			return s.withIO(stdinReader, nil, nil, func() error {
+				return s.executeCommand(cmd)
+			})
+		}
+
+		var buf bytes.Buffer
+		s.withIO(stdinReader, &buf, nil, func() error {
+			return s.executeCommand(cmd)
+		})
+		prevBuf = buf.Bytes()
+	}
+	return nil
+}

internal/shell/expand.go

@@ -0,0 +1,448 @@
+package shell
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+func isVarChar(c byte) bool {
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_'
+}
+
+// expandWord expands $VAR, ${VAR}, $(...), $((...)) in a single token.
+// Quote characters (single/double) are interpreted here and stripped from output.
+func (s *Shell) expandWord(word string) string {
+	// Tilde expansion (only when not quoted)
+	if strings.HasPrefix(word, "~") {
+		home := s.GetVar("HOME")
+		if home == "" {
+			home = os.Getenv("USERPROFILE")
+		}
+		if len(word) == 1 {
+			return home
+		}
+		if word[1] == '/' || word[1] == '\\' {
+			return home + word[1:]
+		}
+	}
+
+	var result strings.Builder
+	inSingle := false
+	inDouble := false
+	i := 0
+
+	for i < len(word) {
+		ch := word[i]
+
+		switch {
+		case ch == '\'' && !inDouble:
+			inSingle = !inSingle
+			i++
+		case ch == '"' && !inSingle:
+			inDouble = !inDouble
+			i++
+		case ch == '\\' && !inSingle:
+			if i+1 < len(word) {
+				next := word[i+1]
+				if inDouble {
+					// In double quotes, only certain chars are escaped
+					switch next {
+					case '$', '`', '"', '\\', '\n':
+						result.WriteByte(next)
+						i += 2
+					default:
+						result.WriteByte('\\')
+						result.WriteByte(next)
+						i += 2
+					}
+				} else {
+					result.WriteByte(next)
+					i += 2
+				}
+			} else {
+				i++
+			}
+		case ch == '$' && !inSingle:
+			i++ // skip $
+			if i >= len(word) {
+				result.WriteByte('$')
+				break
+			}
+			switch word[i] {
+			case '(':
+				if i+1 < len(word) && word[i+1] == '(' {
+					// $(( arithmetic ))
+					j := i + 2
+					depth := 2
+					for j < len(word) {
+						if word[j] == '(' {
+							depth++
+						}
+						if word[j] == ')' {
+							depth--
+							if depth == 0 {
+								j++
+								break
+							}
+						}
+						j++
+					}
+					expr := word[i+2 : j-2]
+					result.WriteString(strconv.Itoa(s.evalArith(expr)))
+					i = j
+				} else {
+					// $( command substitution )
+					j := i + 1
+					depth := 1
+					for j < len(word) {
+						if word[j] == '(' {
+							depth++
+						}
+						if word[j] == ')' {
+							depth--
+							if depth == 0 {
+								break
+							}
+						}
+						j++
+					}
+					cmd := word[i+1 : j]
+					out := s.captureCommand(cmd)
+					result.WriteString(strings.TrimRight(out, "\n"))
+					i = j + 1
+				}
+			case '{':
+				j := i + 1
+				depth := 1
+				for j < len(word) {
+					if word[j] == '{' {
+						depth++
+					}
+					if word[j] == '}' {
+						depth--
+						if depth == 0 {
+							break
+						}
+					}
+					j++
+				}
+				varExpr := word[i+1 : j]
+				result.WriteString(s.evalVarExpr(varExpr))
+				i = j + 1
+			case '?':
+				result.WriteString(s.vars["?"])
+				i++
+			case '$':
+				result.WriteString(fmt.Sprintf("%d", os.Getpid()))
+				i++
+			case '!':
+				result.WriteString(s.vars["!"])
+				i++
+			case '#':
+				result.WriteString(s.vars["#"])
+				i++
+			case '@':
+				result.WriteString(s.vars["@"])
+				i++
+			case '*':
+				result.WriteString(s.vars["*"])
+				i++
+			default:
+				j := i
+				for j < len(word) && isVarChar(word[j]) {
+					j++
+				}
+				if j == i {
+					result.WriteByte('$')
+				} else {
+					result.WriteString(s.getVar(word[i:j]))
+					i = j
+				}
+			}
+		default:
+			result.WriteByte(ch)
+			i++
+		}
+	}
+	return result.String()
+}
+
+func (s *Shell) getVar(name string) string {
+	if v, ok := s.vars[name]; ok {
+		return v
+	}
+	return os.Getenv(name)
+}
+
+func (s *Shell) evalVarExpr(expr string) string {
+	// ${#VAR} — string length
+	if strings.HasPrefix(expr, "#") {
+		return strconv.Itoa(len(s.getVar(expr[1:])))
+	}
+	// ${VAR:-default}
+	if idx := strings.Index(expr, ":-"); idx >= 0 {
+		varName := expr[:idx]
+		if v := s.getVar(varName); v != "" {
+			return v
+		}
+		return s.expandWord(expr[idx+2:])
+	}
+	// ${VAR:=default}
+	if idx := strings.Index(expr, ":="); idx >= 0 {
+		varName := expr[:idx]
+		if v := s.getVar(varName); v != "" {
+			return v
+		}
+		expanded := s.expandWord(expr[idx+2:])
+		s.vars[varName] = expanded
+		return expanded
+	}
+	// ${VAR:+alt}
+	if idx := strings.Index(expr, ":+"); idx >= 0 {
+		varName := expr[:idx]
+		if v := s.getVar(varName); v != "" {
+			return s.expandWord(expr[idx+2:])
+		}
+		return ""
+	}
+	// ${VAR%pattern} — strip shortest suffix
+	if idx := strings.Index(expr, "%"); idx >= 0 {
+		varName := expr[:idx]
+		pattern := expr[idx+1:]
+		v := s.getVar(varName)
+		if strings.HasSuffix(v, pattern) {
+			return v[:len(v)-len(pattern)]
+		}
+		return v
+	}
+	// ${VAR#pattern} — strip shortest prefix
+	if idx := strings.Index(expr, "#"); idx >= 0 {
+		varName := expr[:idx]
+		pattern := expr[idx+1:]
+		v := s.getVar(varName)
+		if strings.HasPrefix(v, pattern) {
+			return v[len(pattern):]
+		}
+		return v
+	}
+	return s.getVar(expr)
+}
+
+// captureCommand runs a command and returns its stdout as a string.
+func (s *Shell) captureCommand(cmd string) string {
+	var buf bytes.Buffer
+	s.withIO(nil, &buf, nil, func() error {
+		return s.Execute(cmd)
+	})
+	return buf.String()
+}
+
+// evalArith evaluates a shell arithmetic expression.
+func (s *Shell) evalArith(expr string) int {
+	expr = strings.TrimSpace(s.expandWord(expr))
+	// Expand bare variable names (e.g. i+1 → value_of_i + 1)
+	expr = s.expandArithVars(expr)
+	return evalArithExpr(expr)
+}
+
+// expandArithVars replaces bare identifier names with their shell variable values.
+func (s *Shell) expandArithVars(expr string) string {
+	var result strings.Builder
+	i := 0
+	for i < len(expr) {
+		c := expr[i]
+		// Identifier start (letter or _), but not a digit
+		if (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' {
+			j := i
+			for j < len(expr) && isVarChar(expr[j]) {
+				j++
+			}
+			varName := expr[i:j]
+			val := s.getVar(varName)
+			if val == "" {
+				val = "0"
+			}
+			result.WriteString(val)
+			i = j
+		} else {
+			result.WriteByte(c)
+			i++
+		}
+	}
+	return result.String()
+}
+
+func evalArithExpr(expr string) int {
+	expr = strings.TrimSpace(expr)
+	if n, err := strconv.Atoi(expr); err == nil {
+		return n
+	}
+	// Strip outer parens
+	if strings.HasPrefix(expr, "(") && strings.HasSuffix(expr, ")") {
+		return evalArithExpr(expr[1 : len(expr)-1])
+	}
+	// Operators in precedence order (lowest first so we split on last occurrence)
+	for _, op := range []string{"+", "-", "*", "/", "%"} {
+		if idx := findBinaryOp(expr, op); idx >= 0 {
+			left := evalArithExpr(expr[:idx])
+			right := evalArithExpr(expr[idx+1:])
+			switch op {
+			case "+":
+				return left + right
+			case "-":
+				return left - right
+			case "*":
+				return left * right
+			case "/":
+				if right == 0 {
+					return 0
+				}
+				return left / right
+			case "%":
+				if right == 0 {
+					return 0
+				}
+				return left % right
+			}
+		}
+	}
+	return 0
+}
+
+func findBinaryOp(expr, op string) int {
+	depth := 0
+	for i := len(expr) - 1; i >= 0; i-- {
+		switch expr[i] {
+		case ')':
+			depth++
+		case '(':
+			depth--
+		}
+		if depth != 0 {
+			continue
+		}
+		if expr[i:i+1] == op {
+			if (op == "-" || op == "+") && i == 0 {
+				continue
+			}
+			return i
+		}
+	}
+	return -1
+}
+
+// expandGlob expands glob patterns; returns original if no match.
+func (s *Shell) expandGlob(word string) []string {
+	if !strings.ContainsAny(word, "*?[") {
+		return []string{word}
+	}
+	matches, err := filepath.Glob(word)
+	if err != nil || len(matches) == 0 {
+		return []string{word}
+	}
+	return matches
+}
+
+// tokenize splits input into tokens, expands variables, handles quotes and globs.
+func (s *Shell) tokenize(input string) []string {
+	var rawTokens []string
+	current := strings.Builder{}
+	inSingle := false
+	inDouble := false
+	parenDepth := 0   // nesting depth inside $(...) or $((...))
+	pendingDollar := false // true after $ when next char is (
+	wasQuoted := false
+
+	flush := func() {
+		if current.Len() > 0 {
+			tok := current.String()
+			if wasQuoted {
+				tok = "\x00q" + tok
+			}
+			rawTokens = append(rawTokens, tok)
+			current.Reset()
+			wasQuoted = false
+			pendingDollar = false
+		}
+	}
+
+	for i := 0; i < len(input); i++ {
+		c := input[i]
+		switch {
+		case c == '\'' && !inDouble && parenDepth == 0:
+			inSingle = !inSingle
+			wasQuoted = true
+			current.WriteByte(c)
+		case c == '"' && !inSingle && parenDepth == 0:
+			inDouble = !inDouble
+			wasQuoted = true
+			current.WriteByte(c)
+		case c == '$' && !inSingle && i+1 < len(input) && (input[i+1] == '(' || input[i+1] == '{'):
+			// Mark that the next ( opens a substitution — don't increment depth here
+			if input[i+1] == '(' {
+				pendingDollar = true
+			}
+			current.WriteByte(c)
+		case c == '(' && !inSingle && !inDouble && (parenDepth > 0 || pendingDollar):
+			parenDepth++
+			pendingDollar = false
+			current.WriteByte(c)
+		case c == ')' && !inSingle && !inDouble && parenDepth > 0:
+			parenDepth--
+			current.WriteByte(c)
+		case c == '{' && !inSingle && !inDouble && parenDepth > 0:
+			parenDepth++
+			current.WriteByte(c)
+		case c == '}' && !inSingle && !inDouble && parenDepth > 0:
+			parenDepth--
+			current.WriteByte(c)
+		case (c == ' ' || c == '\t') && !inSingle && !inDouble && parenDepth == 0:
+			flush()
+		case c == '#' && !inSingle && !inDouble && parenDepth == 0 && current.Len() == 0:
+			// Inline comment: # at start of a new token — discard the rest of the input
+			goto doneTokenizing
+		default:
+			pendingDollar = false
+			current.WriteByte(c)
+		}
+	}
+doneTokenizing:
+	flush()
+
+	// Handle variable assignment on token[0]: FOO=bar
+	if len(rawTokens) > 0 {
+		tok := rawTokens[0]
+		clean := strings.TrimPrefix(tok, "\x00q")
+		if eqIdx := strings.Index(clean, "="); eqIdx > 0 {
+			name := clean[:eqIdx]
+			if isValidIdentifier(name) && !strings.Contains(clean[:eqIdx], "$") {
+				value := s.expandWord(clean[eqIdx+1:])
+				s.vars[name] = value
+				os.Setenv(name, value)
+				rawTokens = rawTokens[1:]
+				if len(rawTokens) == 0 {
+					return nil
+				}
+			}
+		}
+	}
+
+	var result []string
+	for _, tok := range rawTokens {
+		quoted := strings.HasPrefix(tok, "\x00q")
+		if quoted {
+			tok = tok[2:]
+		}
+		expanded := s.expandWord(tok)
+		if !quoted && strings.ContainsAny(expanded, "*?[") {
+			result = append(result, s.expandGlob(expanded)...)
+		} else {
+			result = append(result, expanded)
+		}
+	}
+	return result
+}

internal/shell/shell.go

@@ -1,30 +1,54 @@
 package shell
 
 import (
-    "bytes"
 	"fmt"
 	"io"
 	"os"
-    "os/exec"
-    "path/filepath"
 	"strings"
 )
 
+// Sentinel errors for control flow
+type breakErr struct{ n int }
+type continueErr struct{ n int }
+type returnErr struct{ code int }
+
+func (e breakErr) Error() string    { return fmt.Sprintf("break %d", e.n) }
+func (e continueErr) Error() string { return fmt.Sprintf("continue %d", e.n) }
+func (e returnErr) Error() string   { return fmt.Sprintf("return %d", e.code) }
+
+// exitCodeErr carries a non-zero exit code that sets $? without a message.
+// Used by functions, test, false, etc.
+type exitCodeErr struct{ code int }
+
+func (e exitCodeErr) Error() string { return "" }
+
 type Shell struct {
 	vars     map[string]string
 	builtins map[string]func([]string) error
+	funcs    map[string]string // function name → body
 	lastExit int
+	Stdin    io.Reader
+	Stdout   io.Writer
+	Stderr   io.Writer
+	args     []string
 }
 
 func New() *Shell {
 	s := &Shell{
 		vars:   map[string]string{},
-        lastExit: 0,
+		funcs:  map[string]string{},
+		Stdin:  os.Stdin,
+		Stdout: os.Stdout,
+		Stderr: os.Stderr,
 	}
 	s.initBuiltins()
 	s.vars["SHELL"] = "bash-for-windows"
-    s.vars["BASH_VERSION"] = "1.0.0"
+	s.vars["BASH_VERSION"] = "5.2.15(1)-release"
 	s.vars["?"] = "0"
+	s.vars["#"] = "0"
+	s.vars["@"] = ""
+	s.vars["*"] = ""
+	s.vars["!"] = ""
 	if pwd, err := os.Getwd(); err == nil {
 		s.vars["PWD"] = pwd
 	}
@@ -34,14 +58,296 @@ func New() *Shell {
 	return s
 }
 
+func (s *Shell) SetArgs(args []string) {
+	s.args = args
+	s.vars["#"] = fmt.Sprintf("%d", len(args))
+	s.vars["@"] = strings.Join(args, " ")
+	s.vars["*"] = strings.Join(args, " ")
+	for i, a := range args {
+		s.vars[fmt.Sprintf("%d", i+1)] = a
+	}
+}
+
+func (s *Shell) GetVar(name string) string {
+	if v, ok := s.vars[name]; ok {
+		return v
+	}
+	return os.Getenv(name)
+}
+
+func (s *Shell) SetVar(name, value string) {
+	s.vars[name] = value
+}
+
+// Execute runs commands from the given input string.
 func (s *Shell) Execute(input string) error {
-    input = strings.TrimSpace(input)
-    if input == "" {
+	input = strings.ReplaceAll(input, "\\\n", " ")
+	blocks := parseBlocks(input)
+	for _, block := range blocks {
+		if err := s.executeBlock(block); err != nil {
+			switch err.(type) {
+			case breakErr, continueErr, returnErr:
+				return err
+			}
+			s.setExitCode(err)
+		}
+	}
 	return nil
+}
+
+// IsIncomplete returns true if the input is an incomplete multi-line construct.
+func IsIncomplete(input string) bool {
+	stmts := splitStatements(input)
+	depth := 0
+	inSingle := false
+	inDouble := false
+	for _, ch := range input {
+		switch ch {
+		case '\'':
+			if !inDouble {
+				inSingle = !inSingle
+			}
+		case '"':
+			if !inSingle {
+				inDouble = !inDouble
+			}
+		}
+	}
+	if inSingle || inDouble {
+		return true
+	}
+	for _, stmt := range stmts {
+		w := firstWord(stmt)
+		switch w {
+		case "if", "for", "while", "until":
+			depth++
+		case "fi", "done", "esac":
+			depth--
+		case "{":
+			depth++
+		case "}":
+			if depth > 0 {
+				depth--
+			}
+		}
+		if isFuncDefStart(stmt) && strings.HasSuffix(strings.TrimSpace(stmt), "{") {
+			depth++
+		}
+	}
+	return depth > 0
+}
+
+// parseBlocks groups statements into logical execution units.
+// Multi-line if/for/while/function blocks are gathered into single entries.
+func parseBlocks(input string) []string {
+	stmts := splitStatements(input)
+	var blocks []string
+	var current []string
+	kwDepth := 0   // if/for/while/until → fi/done nesting
+	inFunc := false
+	funcKwDepth := 0 // keyword nesting inside a function body
+
+	for _, stmt := range stmts {
+		stmt = strings.TrimSpace(stmt)
+		if stmt == "" || strings.HasPrefix(stmt, "#") {
+			continue
+		}
+		w := firstWord(stmt)
+
+		if !inFunc {
+			// Detect function definition opening with `{`
+			if isFuncDefStart(stmt) && strings.Contains(stmt, "{") {
+				braceIdx := strings.Index(stmt, "{")
+				// Count keywords after the { on this same line
+				funcKwDepth = 0
+				for _, p := range splitStatements(stmt[braceIdx+1:]) {
+					switch firstWord(p) {
+					case "if", "for", "while", "until":
+						funcKwDepth++
+					case "fi", "done", "esac":
+						funcKwDepth--
+					}
+				}
+				// If the line also ends with } it's a self-contained function
+				if strings.HasSuffix(stmt, "}") {
+					current = append(current, stmt)
+					blocks = append(blocks, strings.Join(current, "\n"))
+					current = nil
+					funcKwDepth = 0
+					continue
+				}
+				inFunc = true
+				current = append(current, stmt)
+				continue
 			}
 
-    lines := strings.Split(input, "\n")
-    for _, line := range lines {
+			switch w {
+			case "if", "for", "while", "until":
+				kwDepth++
+			}
+			kwDepth += embeddedKwDepth(stmt)
+			current = append(current, stmt)
+			switch w {
+			case "fi", "done", "esac":
+				kwDepth--
+			case "}":
+				if kwDepth > 0 {
+					kwDepth--
+				}
+			}
+			if kwDepth <= 0 && len(current) > 0 {
+				kwDepth = 0
+				blocks = append(blocks, strings.Join(current, "\n"))
+				current = nil
+			}
+		} else {
+			// Inside function body — watch for } at funcKwDepth==0
+			if w == "}" && funcKwDepth <= 0 {
+				current = append(current, stmt)
+				blocks = append(blocks, strings.Join(current, "\n"))
+				current = nil
+				inFunc = false
+				funcKwDepth = 0
+				continue
+			}
+			switch w {
+			case "if", "for", "while", "until":
+				funcKwDepth++
+			case "fi", "done", "esac":
+				funcKwDepth--
+			}
+			funcKwDepth += embeddedKwDepth(stmt)
+			current = append(current, stmt)
+		}
+	}
+	if len(current) > 0 {
+		blocks = append(blocks, strings.Join(current, "\n"))
+	}
+	return blocks
+}
+
+// embeddedKwDepth returns the net depth change from keywords that appear
+// after do/then/else/elif within a single statement (excluding the first word,
+// which is handled separately by the caller).
+func embeddedKwDepth(stmt string) int {
+	words := strings.Fields(stmt)
+	delta := 0
+	for j := 1; j < len(words); j++ {
+		switch words[j-1] {
+		case "do", "then", "else", "elif":
+			switch words[j] {
+			case "if", "for", "while", "until":
+				delta++
+			case "fi", "done", "esac":
+				delta--
+			}
+		}
+	}
+	return delta
+}
+
+// splitStatements splits input on semicolons and newlines, respecting quotes.
+func splitStatements(input string) []string {
+	var result []string
+	current := strings.Builder{}
+	inSingle := false
+	inDouble := false
+
+	for i := 0; i < len(input); i++ {
+		c := input[i]
+		switch {
+		case c == '\'' && !inDouble:
+			inSingle = !inSingle
+			current.WriteByte(c)
+		case c == '"' && !inSingle:
+			inDouble = !inDouble
+			current.WriteByte(c)
+		case (c == ';' || c == '\n') && !inSingle && !inDouble:
+			if s := strings.TrimSpace(current.String()); s != "" {
+				result = append(result, s)
+			}
+			current.Reset()
+		default:
+			current.WriteByte(c)
+		}
+	}
+	if s := strings.TrimSpace(current.String()); s != "" {
+		result = append(result, s)
+	}
+	return result
+}
+
+func firstWord(s string) string {
+	fields := strings.Fields(s)
+	if len(fields) == 0 {
+		return ""
+	}
+	return fields[0]
+}
+
+func afterWord(s string) string {
+	for i, ch := range s {
+		if ch == ' ' || ch == '\t' {
+			return strings.TrimSpace(s[i:])
+		}
+	}
+	return ""
+}
+
+func isFuncDefStart(stmt string) bool {
+	if strings.HasPrefix(stmt, "function ") {
+		return true
+	}
+	for i, ch := range stmt {
+		if ch == ' ' || ch == '\t' {
+			break
+		}
+		if ch == '(' {
+			name := strings.TrimSpace(stmt[:i])
+			return isValidIdentifier(name)
+		}
+	}
+	return false
+}
+
+func isValidIdentifier(s string) bool {
+	if len(s) == 0 {
+		return false
+	}
+	for i, c := range s {
+		if i == 0 {
+			if !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_') {
+				return false
+			}
+		} else {
+			if !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_') {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+func (s *Shell) executeBlock(block string) error {
+	block = strings.TrimSpace(block)
+	if block == "" || strings.HasPrefix(block, "#") {
+		return nil
+	}
+	w := firstWord(block)
+	switch w {
+	case "if":
+		return s.executeIf(block)
+	case "for":
+		return s.executeFor(block)
+	case "while":
+		return s.executeWhileUntil(block, false)
+	case "until":
+		return s.executeWhileUntil(block, true)
+	}
+	if isFuncDefStart(block) {
+		return s.defineFunction(block)
+	}
+	for _, line := range strings.Split(block, "\n") {
 		line = strings.TrimSpace(line)
 		if line == "" || strings.HasPrefix(line, "#") {
 			continue
@@ -54,23 +360,20 @@ func (s *Shell) Execute(input string) error {
 }
 
 func (s *Shell) executeLine(line string) error {
-    // Tokenize the line into its components, handling &&, ||, ;
 	return s.executeChain(line)
 }
 
-// executeChain: parse && / || / ; with left-to-right precedence
 func (s *Shell) executeChain(line string) error {
-    // Strategy: split by ; first (semicolons always separate), 
-    // then by &&/|| within each segment
-    segments := splitBySemicolon(line)
-    
-    for _, seg := range segments {
+	for _, seg := range splitBySemicolon(line) {
 		seg = strings.TrimSpace(seg)
 		if seg == "" {
 			continue
 		}
 		if err := s.executeAndOrList(seg); err != nil {
-            // In ; chains, errors in one command don't stop execution
+			switch err.(type) {
+			case breakErr, continueErr, returnErr:
+				return err
+			}
 			s.setExitCode(err)
 		}
 	}
@@ -79,7 +382,7 @@ func (s *Shell) executeChain(line string) error {
 
 func splitBySemicolon(line string) []string {
 	var parts []string
-    current := ""
+	current := strings.Builder{}
 	inSingle := false
 	inDouble := false
 
@@ -88,32 +391,30 @@ func splitBySemicolon(line string) []string {
 		switch {
 		case c == '\'' && !inDouble:
 			inSingle = !inSingle
-            current += string(c)
+			current.WriteByte(c)
 		case c == '"' && !inSingle:
 			inDouble = !inDouble
-            current += string(c)
+			current.WriteByte(c)
 		case c == ';' && !inSingle && !inDouble:
-            parts = append(parts, current)
-            current = ""
+			parts = append(parts, current.String())
+			current.Reset()
 		default:
-            current += string(c)
+			current.WriteByte(c)
 		}
 	}
-    if current != "" {
-        parts = append(parts, current)
+	if current.Len() > 0 {
+		parts = append(parts, current.String())
 	}
 	return parts
 }
 
-// executeAndOrList: parse && / || with left-to-right precedence
 func (s *Shell) executeAndOrList(line string) error {
-    type token struct {
+	type tok struct {
 		text string
-        op   string // operator BEFORE this token (except first = "")
+		op   string
 	}
-
-    var tokens []token
-    current := ""
+	var tokens []tok
+	current := strings.Builder{}
 	op := ""
 	inSingle := false
 	inDouble := false
@@ -123,326 +424,86 @@ func (s *Shell) executeAndOrList(line string) error {
 		switch {
 		case c == '\'' && !inDouble:
 			inSingle = !inSingle
-            current += string(c)
+			current.WriteByte(c)
 		case c == '"' && !inSingle:
 			inDouble = !inDouble
-            current += string(c)
-        case c == '&' && !inSingle && !inDouble:
-            if i+1 < len(line) && line[i+1] == '&' {
-                if current != "" {
-                    tokens = append(tokens, token{current, op})
-                    current = ""
-                }
+			current.WriteByte(c)
+		case c == '&' && !inSingle && !inDouble && i+1 < len(line) && line[i+1] == '&':
+			tokens = append(tokens, tok{current.String(), op})
+			current.Reset()
 			op = "&&"
 			i++
-            } else {
-                current += string(c)
-            }
-        case c == '|' && !inSingle && !inDouble:
-            if i+1 < len(line) && line[i+1] == '|' {
-                if current != "" {
-                    tokens = append(tokens, token{current, op})
-                    current = ""
-                }
+		case c == '|' && !inSingle && !inDouble && i+1 < len(line) && line[i+1] == '|':
+			tokens = append(tokens, tok{current.String(), op})
+			current.Reset()
 			op = "||"
 			i++
-            } else {
-                current += string(c)
-            }
 		default:
-            current += string(c)
+			current.WriteByte(c)
 		}
 	}
-    if current != "" {
-        tokens = append(tokens, token{current, op})
-    }
-
-    if len(tokens) == 0 {
-        return nil
+	if current.Len() > 0 {
+		tokens = append(tokens, tok{current.String(), op})
 	}
 
 	var lastErr error
-    for i, tok := range tokens {
-        cmd := strings.TrimSpace(tok.text)
+	for i, t := range tokens {
+		cmd := strings.TrimSpace(t.text)
 		if cmd == "" {
 			continue
 		}
-
-        shouldRun := true
-        if i > 0 && tok.op == "&&" {
-            shouldRun = (lastErr == nil)
-        } else if i > 0 && tok.op == "||" {
-            shouldRun = (lastErr != nil)
+		run := i == 0
+		if i > 0 {
+			run = (t.op == "&&" && lastErr == nil) || (t.op == "||" && lastErr != nil)
 		}
-
-        if shouldRun {
+		if run {
 			err := s.executePipeline(cmd)
 			lastErr = err
 			s.setExitCode(err)
 		}
 	}
-
 	return lastErr
 }
 
 func (s *Shell) setExitCode(err error) {
-    if err != nil {
-        s.vars["?"] = "1"
-    } else {
+	if err == nil {
 		s.vars["?"] = "0"
-    }
-}
-
-func (s *Shell) executePipeline(input string) error {
-    input = strings.TrimSpace(input)
-    if input == "" {
-        return nil
-    }
-
-    if strings.Contains(input, "|") {
-        return s.doPipe(input)
-    }
-
-    return s.executeCommand(input)
-}
-
-func (s *Shell) executeCommand(input string) error {
-    parts := s.tokenize(input)
-    if len(parts) == 0 {
-        return nil
-    }
-
-    cmdName := parts[0]
-    args := parts[1:]
-
-    if alias, ok := aliases[cmdName]; ok {
-        fullCmd := alias
-        if len(args) > 0 {
-            fullCmd += " " + strings.Join(args, " ")
-        }
-        return s.Execute(fullCmd)
-    }
-
-    if builtin, ok := s.builtins[cmdName]; ok {
-        return builtin(args)
-    }
-
-    return s.executeExternal(cmdName, args)
-}
-
-func (s *Shell) tokenize(input string) []string {
-    var tokens []string
-    current := ""
-    inSingle := false
-    inDouble := false
-
-    for i := 0; i < len(input); i++ {
-        c := input[i]
-
-        switch {
-        case c == '\'' && !inDouble:
-            inSingle = !inSingle
-        case c == '"' && !inSingle:
-            inDouble = !inDouble
-        case (c == ' ' || c == '\t') && !inSingle && !inDouble:
-            if current != "" {
-                tokens = append(tokens, current)
-                current = ""
-            }
-        case c == '=' && !inSingle && !inDouble:
-            current += string(c)
-        default:
-            current += string(c)
-        }
-    }
-
-    if current != "" {
-        tokens = append(tokens, current)
-    }
-
-    for i, tok := range tokens {
-        if strings.HasPrefix(tok, "$") {
-            key := tok[1:]
-            if strings.HasPrefix(key, "{") && strings.HasSuffix(key, "}") {
-                key = key[1 : len(key)-1]
-            }
-            if val, ok := s.vars[key]; ok {
-                tokens[i] = val
-            } else if val := os.Getenv(key); val != "" {
-                tokens[i] = val
-            }
-        }
-    }
-
-    varAssignIdx := -1
-    for i, tok := range tokens {
-        if strings.Contains(tok, "=") && i == 0 {
-            eqIdx := strings.Index(tok, "=")
-            if eqIdx > 0 && eqIdx < len(tok)-1 {
-                name := tok[:eqIdx]
-                value := tok[eqIdx+1:]
-                s.vars[name] = value
-                os.Setenv(name, value)
-                varAssignIdx = i
-            }
-        }
-    }
-    if varAssignIdx == 0 && len(tokens) > 1 {
-        tokens = tokens[1:]
-    }
-
-    return tokens
-}
-
-func (s *Shell) executeExternal(cmdName string, args []string) error {
-    cmdPath := findExecutable(cmdName)
-    if cmdPath == "" {
-        return fmt.Errorf("%s: command not found", cmdName)
-    }
-
-    cmd := exec.Command(cmdPath, args...)
-    cmd.Stdin = os.Stdin
-    cmd.Stdout = os.Stdout
-    cmd.Stderr = os.Stderr
-
-    return cmd.Run()
-}
-
-func findExecutable(name string) string {
-    if _, err := os.Stat(name); err == nil {
-        if info, _ := os.Stat(name); info != nil && !info.IsDir() {
-            abs, _ := filepath.Abs(name)
-            return abs
-        }
-    }
-
-    path := os.Getenv("PATH")
-    for _, dir := range filepath.SplitList(path) {
-        fullPath := filepath.Join(dir, name)
-        info, err := os.Stat(fullPath)
-        if err == nil && !info.IsDir() {
-            return fullPath
-        }
-        fullPathExe := fullPath + ".exe"
-        info, err = os.Stat(fullPathExe)
-        if err == nil && !info.IsDir() {
-            return fullPathExe
-        }
-    }
-    return ""
-}
-
-func (s *Shell) doPipe(input string) error {
-    commands := strings.Split(input, "|")
-
-    type cmdPart struct {
-        name    string
-        args    []string
-        builtin bool
-    }
-
-    var parts []cmdPart
-    for _, part := range commands {
-        part = strings.TrimSpace(part)
-        if part == "" {
-            continue
-        }
-        tokens := s.tokenize(part)
-        if len(tokens) == 0 {
-            continue
-        }
-        name := tokens[0]
-        _, isBuiltin := s.builtins[name]
-        parts = append(parts, cmdPart{name, tokens[1:], isBuiltin})
-    }
-
-    if len(parts) == 0 {
-        return nil
-    }
-
-    var prevOutput []byte
-
-    for i, p := range parts {
-        var input []byte
-        if i > 0 {
-            input = prevOutput
-        }
-
-        if p.builtin {
-            output, err := s.captureBuiltin(p.name, p.args, input)
-            if err != nil {
-                // Don't return error, let it pass
-                prevOutput = nil
-                if i == len(parts)-1 {
-                    return err
-                }
-                continue
-            }
-            if i == len(parts)-1 {
-                fmt.Print(string(output))
+		s.lastExit = 0
+	} else if ec, ok := err.(exitCodeErr); ok {
+		s.vars["?"] = fmt.Sprintf("%d", ec.code)
+		s.lastExit = ec.code
 	} else {
-                prevOutput = output
+		s.vars["?"] = "1"
+		s.lastExit = 1
 	}
-        } else {
-            cmdPath := findExecutable(p.name)
-            if cmdPath == "" {
-                return fmt.Errorf("%s: command not found", p.name)
-            }
-            cmd := exec.Command(cmdPath, p.args...)
-            cmd.Stderr = os.Stderr
-
-            if i == 0 && len(input) == 0 {
-                cmd.Stdin = os.Stdin
-            } else if len(input) > 0 {
-                stdin, _ := cmd.StdinPipe()
-                go func() {
-                    stdin.Write(input)
-                    stdin.Close()
-                }()
-            }
-
-            if i == len(parts)-1 {
-                cmd.Stdout = os.Stdout
-                if err := cmd.Run(); err != nil {
-                    return err
-                }
-            } else {
-                output, err := cmd.Output()
-                if err != nil {
-                    return err
-                }
-                prevOutput = output
-            }
-        }
-    }
-
-    return nil
 }
 
-func (s *Shell) captureBuiltin(name string, args []string, input []byte) ([]byte, error) {
-    oldStdout := os.Stdout
-    oldStdin := os.Stdin
-    r, w, _ := os.Pipe()
-    os.Stdout = w
-
-    if len(input) > 0 {
-        ir, iw, _ := os.Pipe()
-        iw.Write(input)
-        iw.Close()
-        os.Stdin = ir
-        defer ir.Close()
+// BuiltinNames returns a sorted list of all registered builtin names (for tab completion).
+func (s *Shell) BuiltinNames() []string {
+	names := make([]string, 0, len(s.builtins)+len(s.funcs))
+	for k := range s.builtins {
+		names = append(names, k)
 	}
-
-    fn := s.builtins[name]
-    err := fn(args)
-
-    w.Close()
-    os.Stdout = oldStdout
-    os.Stdin = oldStdin
-
-    var buf bytes.Buffer
-    io.Copy(&buf, r)
-    r.Close()
-
-    return buf.Bytes(), err
+	for k := range s.funcs {
+		names = append(names, k)
+	}
+	return names
+}
+
+// withIO temporarily swaps stdin/stdout/stderr, runs fn, then restores.
+// Pass nil to leave the corresponding stream unchanged.
+func (s *Shell) withIO(stdin io.Reader, stdout io.Writer, stderr io.Writer, fn func() error) error {
+	oldIn, oldOut, oldErr := s.Stdin, s.Stdout, s.Stderr
+	if stdin != nil {
+		s.Stdin = stdin
+	}
+	if stdout != nil {
+		s.Stdout = stdout
+	}
+	if stderr != nil {
+		s.Stderr = stderr
+	}
+	err := fn()
+	s.Stdin, s.Stdout, s.Stderr = oldIn, oldOut, oldErr
+	return err
 }