diff --git a/internal/shellhook/shellhook.go b/internal/shellhook/shellhook.go
index b703553..13c9714 100644
--- a/internal/shellhook/shellhook.go
+++ b/internal/shellhook/shellhook.go
@@ -10,12 +10,81 @@ import (
 	"strings"
 )
 
+// Shell identifies a shell type.
+type Shell int
+
+const (
+	ShellUnknown Shell = iota
+	ShellPowerShell
+	ShellBash
+	ShellZsh
+)
+
+// detectShellEnv is the detection function variable, replaceable in tests.
+var detectShellEnv = detectShell
+
+// detectShell returns the active shell based on environment heuristics.
+func detectShell() Shell {
+	if os.Getenv("PSModulePath") != "" {
+		return ShellPowerShell
+	}
+	sh := os.Getenv("SHELL")
+	if strings.Contains(sh, "zsh") {
+		return ShellZsh
+	}
+	if strings.Contains(sh, "bash") {
+		return ShellBash
+	}
+	return ShellUnknown
+}
+
+// primaryProfileIndex returns the index into candidates that corresponds to the
+// detected shell's profile, or -1 if none matches.
+func primaryProfileIndex(shell Shell, candidates []string) int {
+	for i, c := range candidates {
+		switch shell {
+		case ShellPowerShell:
+			if strings.HasSuffix(c, ".ps1") {
+				return i
+			}
+		case ShellZsh:
+			if strings.HasSuffix(c, ".zshrc") {
+				return i
+			}
+		case ShellBash:
+			if strings.HasSuffix(c, ".bashrc") {
+				return i
+			}
+		}
+	}
+	return -1
+}
+
+// ensureFileExists creates the file (and parent directories) if it does not
+// already exist. Returns nil if the file already exists.
+func ensureFileExists(path string) error {
+	if _, err := os.Stat(path); err == nil {
+		return nil
+	}
+	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
+		return err
+	}
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	return f.Close()
+}
+
 // Result describes what happened to a single profile file.
 type Result struct {
 	Path    string
 	Updated bool // false = already present (Add) or line not found (Remove)
 }
 
+// currentOS is the GOOS value used by candidateProfiles, replaceable in tests.
+var currentOS = runtime.GOOS
+
 // homeDir is a variable so tests can substitute a temp directory.
 var homeDir = os.UserHomeDir
 
@@ -26,7 +95,7 @@ func candidateProfiles() ([]string, error) {
 	if err != nil {
 		return nil, err
 	}
-	return profilesForOS(runtime.GOOS, home), nil
+	return profilesForOS(currentOS, home), nil
 }
 
 // profilesForOS returns candidate profile paths for a given GOOS and home
@@ -49,13 +118,20 @@ func profilesForOS(goos, home string) []string {
 }
 
 // Add appends comment and line to every existing profile that does not
-// already contain line as a complete line. Returns one Result per
-// candidate profile found on disk.
+// already contain line as a complete line. The detected shell's profile
+// is created if it does not exist. Returns one Result per candidate
+// profile found on disk.
 func Add(line, comment string) ([]Result, error) {
 	candidates, err := candidateProfiles()
 	if err != nil {
 		return nil, err
 	}
+	shell := detectShellEnv()
+	if idx := primaryProfileIndex(shell, candidates); idx >= 0 {
+		if err := ensureFileExists(candidates[idx]); err != nil {
+			return nil, fmt.Errorf("creating profile %s: %w", candidates[idx], err)
+		}
+	}
 	return addToProfiles(line, comment, candidates)
 }
 
diff --git a/internal/shellhook/shellhook_test.go b/internal/shellhook/shellhook_test.go
index 20c3f62..8581fae 100644
--- a/internal/shellhook/shellhook_test.go
+++ b/internal/shellhook/shellhook_test.go
@@ -336,3 +336,156 @@ func TestRemove_WindowsPowerShellPath(t *testing.T) {
 		t.Error("hook should be removed from PowerShell profile")
 	}
 }
+
+// --- Shell detection tests ---
+
+func TestDetectShell_PowerShell(t *testing.T) {
+	orig := detectShellEnv
+	defer func() { detectShellEnv = orig }()
+
+	detectShellEnv = func() Shell { return ShellPowerShell }
+	if detectShellEnv() != ShellPowerShell {
+		t.Error("expected PowerShell")
+	}
+}
+
+func TestDetectShell_Zsh(t *testing.T) {
+	orig := detectShellEnv
+	defer func() { detectShellEnv = orig }()
+
+	detectShellEnv = func() Shell { return ShellZsh }
+	if detectShellEnv() != ShellZsh {
+		t.Error("expected Zsh")
+	}
+}
+
+func TestDetectShell_Bash(t *testing.T) {
+	orig := detectShellEnv
+	defer func() { detectShellEnv = orig }()
+
+	detectShellEnv = func() Shell { return ShellBash }
+	if detectShellEnv() != ShellBash {
+		t.Error("expected Bash")
+	}
+}
+
+func TestPrimaryProfileIndex(t *testing.T) {
+	candidates := []string{
+		"/home/user/Documents/PowerShell/Microsoft.PowerShell_profile.ps1",
+		"/home/user/.bashrc",
+		"/home/user/.zshrc",
+	}
+	if idx := primaryProfileIndex(ShellPowerShell, candidates); idx != 0 {
+		t.Errorf("PowerShell: want 0, got %d", idx)
+	}
+	if idx := primaryProfileIndex(ShellBash, candidates); idx != 1 {
+		t.Errorf("Bash: want 1, got %d", idx)
+	}
+	if idx := primaryProfileIndex(ShellZsh, candidates); idx != 2 {
+		t.Errorf("Zsh: want 2, got %d", idx)
+	}
+	if idx := primaryProfileIndex(ShellUnknown, candidates); idx != -1 {
+		t.Errorf("Unknown: want -1, got %d", idx)
+	}
+}
+
+func TestEnsureFileExists_CreatesFileAndDirs(t *testing.T) {
+	dir := t.TempDir()
+	target := filepath.Join(dir, "sub", "dir", "profile.ps1")
+
+	if err := ensureFileExists(target); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	info, err := os.Stat(target)
+	if err != nil {
+		t.Fatalf("file should exist: %v", err)
+	}
+	if info.Size() != 0 {
+		t.Errorf("newly created file should be empty, got %d bytes", info.Size())
+	}
+}
+
+func TestEnsureFileExists_ExistingFileUnchanged(t *testing.T) {
+	dir := t.TempDir()
+	target := filepath.Join(dir, ".zshrc")
+	if err := os.WriteFile(target, []byte("existing content\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ensureFileExists(target); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	data, _ := os.ReadFile(target)
+	if string(data) != "existing content\n" {
+		t.Error("existing file should not be modified")
+	}
+}
+
+func TestAdd_CreatesProfileForDetectedShell(t *testing.T) {
+	dir := t.TempDir()
+	psPath := filepath.Join(dir, "Documents", "PowerShell", "Microsoft.PowerShell_profile.ps1")
+
+	orig := detectShellEnv
+	defer func() { detectShellEnv = orig }()
+	detectShellEnv = func() Shell { return ShellPowerShell }
+
+	origOS := currentOS
+	defer func() { currentOS = origOS }()
+	currentOS = "windows"
+
+	// Profile doesn't exist yet — Add should create it
+	origHome := homeDir
+	defer func() { homeDir = origHome }()
+	homeDir = func() (string, error) { return dir, nil }
+
+	results, err := Add("sap-devs tip", "# SAP developer tips")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	found := false
+	for _, r := range results {
+		if r.Path == psPath && r.Updated {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("expected PowerShell profile to be created and updated, got %+v", results)
+	}
+	data, _ := os.ReadFile(psPath)
+	if !strings.Contains(string(data), "sap-devs tip") {
+		t.Error("hook should be present in newly created PowerShell profile")
+	}
+}
+
+func TestAdd_DetectedShellZsh_CreatesZshrc(t *testing.T) {
+	dir := t.TempDir()
+	zshrc := filepath.Join(dir, ".zshrc")
+
+	orig := detectShellEnv
+	defer func() { detectShellEnv = orig }()
+	detectShellEnv = func() Shell { return ShellZsh }
+
+	origOS := currentOS
+	defer func() { currentOS = origOS }()
+	currentOS = "linux"
+
+	origHome := homeDir
+	defer func() { homeDir = origHome }()
+	homeDir = func() (string, error) { return dir, nil }
+
+	results, err := Add("sap-devs tip", "# SAP developer tips")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	found := false
+	for _, r := range results {
+		if r.Path == zshrc && r.Updated {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("expected .zshrc to be created and updated, got %+v", results)
+	}
+}