✨ Support replacements in startup command (#259)

* feat: allow replacements in startup command
* chore: update readme

Author: liam-mackie

README.md

@@ -295,6 +295,17 @@ startup_command = "nvim tmux.conf"
 preview_command = "bat --color=always ~/c/dotfiles/.config/tmux/tmux.conf"
 ```
 
+### Path substitution
+If you want to use the path of the selected session in your startup or preview command, you can use the `{}` placeholder.  
+This will be replaced with the session's path when the command is run.
+
+An example of this in use is the following, where the `tmuxinator` default_project uses the path as key/value pair using [ERB syntax](https://github.com/tmuxinator/tmuxinator?tab=readme-ov-file#erb):
+```toml
+[default_session]
+startup_command = "tmuxinator start default_project path={}"
+preview_command = "eza --all --git --icons --color=always {}"
+```
+
 ### Multiple windows
 
 If you want your session to have multiple windows you can define windows in your configuration. You can then use these window layouts in your sessions. These windows can be reused as many times as you want and you can add as many windows to each session as you want.

go.mod

@@ -4,6 +4,7 @@ go 1.21
 
 require (
 	github.com/pelletier/go-toml/v2 v2.2.1
+	github.com/petar-dambovaliev/aho-corasick v0.0.0-20250424160509-463d218d4745
 	github.com/stretchr/testify v1.9.0
 	github.com/urfave/cli/v2 v2.27.1
 )

go.sum

@@ -5,6 +5,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pelletier/go-toml/v2 v2.2.1 h1:9TA9+T8+8CUCO2+WYnDLCgrYi9+omqKXyjDtosvtEhg=
 github.com/pelletier/go-toml/v2 v2.2.1/go.mod h1:1t835xjRzz80PqgE6HHgN2JOsmgYu/h4qDAS4n929Rs=
+github.com/petar-dambovaliev/aho-corasick v0.0.0-20250424160509-463d218d4745 h1:Vpr4VgAizEgEZsaMohpw6JYDP+i9Of9dmdY4ufNP6HI=
+github.com/petar-dambovaliev/aho-corasick v0.0.0-20250424160509-463d218d4745/go.mod h1:EHPiTAKtiFmrMldLUNswFwfZ2eJIYBHktdaUTZxYWRw=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=

replacer/replacer.go

@@ -0,0 +1,38 @@
+package replacer
+
+import (
+	ahocorasick "github.com/petar-dambovaliev/aho-corasick"
+)
+
+type Replacer interface {
+	Replace(command string, replacements map[string]string) string
+}
+
+type RealReplacer struct{}
+
+func NewReplacer() Replacer {
+	return &RealReplacer{}
+}
+
+func (r *RealReplacer) Replace(command string, replacements map[string]string) string {
+	dict := make([]string, 0, len(replacements))
+	replacementArray := make([]string, 0, len(replacements))
+	for k, v := range replacements {
+		dict = append(dict, k)
+		replacementArray = append(replacementArray, v)
+	}
+	ac := getAhoCorasick(dict)
+	replacer := ahocorasick.NewReplacer(ac)
+	return replacer.ReplaceAll(command, replacementArray)
+}
+
+func getAhoCorasick(dictionary []string) ahocorasick.AhoCorasick {
+	builder := ahocorasick.NewAhoCorasickBuilder(ahocorasick.Opts{
+		AsciiCaseInsensitive: true,
+		MatchOnlyWholeWords:  true,
+		MatchKind:            ahocorasick.LeftMostFirstMatch,
+		DFA:                  true,
+	})
+
+	return builder.Build(dictionary)
+}

replacer/replacer_test.go

@@ -0,0 +1,44 @@
+package replacer
+
+import (
+	"testing"
+)
+
+type testCase struct {
+	input    string
+	expected string
+}
+
+func TestReplace(t *testing.T) {
+	defaultReplacements := map[string]string{
+		"{}": "hello",
+		"~":  "/home/test",
+	}
+
+	testCases := map[string]testCase{
+		"multiple replacements": {
+			"~/.local/bin/rat {}{}",
+			"/home/test/.local/bin/rat hellohello",
+		},
+		"single replacement": {
+			"/bin/rat {}",
+			"/bin/rat hello",
+		},
+		"no replacement": {
+			"/bin/rat",
+			"/bin/rat",
+		},
+	}
+
+	for name, test := range testCases {
+		t.Run(name, func(t *testing.T) {
+			replacer := NewReplacer()
+			result := replacer.Replace(test.input, defaultReplacements)
+			if result != test.expected {
+				t.Errorf("expected %s, got %s", test.expected, result)
+			}
+		})
+	}
+	t.Run("", func(t *testing.T) {
+	})
+}

seshcli/seshcli.go

@@ -20,6 +20,7 @@ import (
 	"github.com/joshmedeski/sesh/v2/oswrap"
 	"github.com/joshmedeski/sesh/v2/pathwrap"
 	"github.com/joshmedeski/sesh/v2/previewer"
+	"github.com/joshmedeski/sesh/v2/replacer"
 	"github.com/joshmedeski/sesh/v2/runtimewrap"
 	"github.com/joshmedeski/sesh/v2/shell"
 	"github.com/joshmedeski/sesh/v2/startup"
@@ -39,6 +40,7 @@ func App(version string) cli.App {
 	home := home.NewHome(os)
 	shell := shell.NewShell(exec, home)
 	json := json.NewJson()
+	replacer := replacer.NewReplacer()
 
 	// resource dependencies
 	git := git.NewGit(shell)
@@ -60,7 +62,7 @@ func App(version string) cli.App {
 	// core dependencies
 	ls := ls.NewLs(config, shell)
 	lister := lister.NewLister(config, home, tmux, zoxide, tmuxinator)
-	startup := startup.NewStartup(config, lister, tmux, home)
+	startup := startup.NewStartup(config, lister, tmux, home, replacer)
 	namer := namer.NewNamer(path, git, home)
 	connector := connector.NewConnector(config, dir, home, lister, namer, startup, tmux, zoxide, tmuxinator)
 	icon := icon.NewIcon(config)

shell/shell_test.go

@@ -55,4 +55,14 @@ func TestShellPrepareCmd(t *testing.T) {
 		assert.Nil(t, err)
 		assert.Equal(t, []string{"/home/test/.local/bin/rat", "hello"}, cmdParts)
 	})
+
+	// This test case asserts the existing behaviour when the desired replacement is not separated by spaces
+	t.Run("should not use a partial match", func(t *testing.T) {
+		mockHome := new(home.MockHome)
+		shell := &RealShell{home: mockHome}
+		mockHome.On("ExpandHome", "~/.local/bin/rat").Return("/home/test/.local/bin/rat", nil)
+		cmdParts, err := shell.PrepareCmd("~/.local/bin/rat localVar={}", map[string]string{"{}": "hello"})
+		assert.Nil(t, err)
+		assert.Equal(t, []string{"/home/test/.local/bin/rat", "localVar={}"}, cmdParts)
+	})
 }

startup/config.go

@@ -10,7 +10,11 @@ func configStrategy(s *RealStartup, session model.SeshSession) (string, error) {
 	}
 
 	if exists && config.StartupCommand != "" {
-		return config.StartupCommand, nil
+		replacements := map[string]string{
+			"{}": session.Path,
+		}
+
+		return s.replacer.Replace(config.StartupCommand, replacements), nil
 	}
 	return "", nil
 }

startup/defaultconfig.go

@@ -9,7 +9,11 @@ func defaultConfigStrategy(s *RealStartup, session model.SeshSession) (string, e
 
 	defaultConfig := s.config.DefaultSessionConfig
 	if defaultConfig.StartupCommand != "" {
-		return defaultConfig.StartupCommand, nil
+		replacements := map[string]string{
+			"{}": session.Path,
+		}
+
+		return s.replacer.Replace(defaultConfig.StartupCommand, replacements), nil
 	}
 
 	return "", nil

startup/startup.go

@@ -6,6 +6,7 @@ import (
 	"github.com/joshmedeski/sesh/v2/home"
 	"github.com/joshmedeski/sesh/v2/lister"
 	"github.com/joshmedeski/sesh/v2/model"
+	"github.com/joshmedeski/sesh/v2/replacer"
 	"github.com/joshmedeski/sesh/v2/tmux"
 )
 
@@ -14,14 +15,17 @@ type Startup interface {
 }
 
 type RealStartup struct {
-	lister lister.Lister
-	tmux   tmux.Tmux
-	config model.Config
-	home   home.Home
+	lister   lister.Lister
+	tmux     tmux.Tmux
+	config   model.Config
+	home     home.Home
+	replacer replacer.Replacer
 }
 
-func NewStartup(config model.Config, lister lister.Lister, tmux tmux.Tmux, home home.Home) Startup {
-	return &RealStartup{lister, tmux, config, home}
+func NewStartup(
+	config model.Config, lister lister.Lister, tmux tmux.Tmux, home home.Home, replacer replacer.Replacer,
+) Startup {
+	return &RealStartup{lister, tmux, config, home, replacer}
 }
 
 func (s *RealStartup) Exec(session model.SeshSession) (string, error) {