diff --git a/README.md b/README.md
index 54a463d..9d2e01e 100644
--- a/README.md
+++ b/README.md
@@ -343,6 +343,7 @@ If the confgiuration file path isn't specified, the file named `.buildflow.yml`
 * task.import
 * task.input_file
 * task.output_file
+* task.when_file
 * command.command_file
 * command.env[].value_file
 * write_file.template_file
diff --git a/pkg/config/bool.go b/pkg/config/bool.go
index 6cc9c48..db4c2d5 100644
--- a/pkg/config/bool.go
+++ b/pkg/config/bool.go
@@ -25,6 +25,12 @@ func (b *Bool) SetBool(f bool) {
 	b.Fixed = true
 }
 
+func (b *Bool) SetBoolProgram(f expr.BoolProgram) {
+	b.Prog = f
+	b.Fixed = false
+	b.Initialized = true
+}
+
 func (b *Bool) SetDefaultBool(f bool) {
 	if !b.Initialized {
 		b.SetBool(f)
diff --git a/pkg/config/task.go b/pkg/config/task.go
index 071fe2e..a83a749 100644
--- a/pkg/config/task.go
+++ b/pkg/config/task.go
@@ -12,6 +12,7 @@ type Task struct {
 	Name          Template
 	Type          string `yaml:"-"`
 	When          Bool
+	WhenFile      string `yaml:"when_file"`
 	Dependency    Dependency
 	Command       Command
 	ReadFile      ReadFile  `yaml:"read_file"`
diff --git a/pkg/controller/controller.go b/pkg/controller/controller.go
index 646d85c..37d4a72 100644
--- a/pkg/controller/controller.go
+++ b/pkg/controller/controller.go
@@ -408,6 +408,25 @@ func (ctrl Controller) readScript(p, wd string, scr *config.Script) error {
 	return nil
 }
 
+func (ctrl Controller) readBoolScript(p, wd string, scr *config.Bool) error {
+	if p == "" {
+		return nil
+	}
+	if !filepath.IsAbs(p) {
+		p = filepath.Join(wd, p)
+	}
+	result, err := ctrl.FileReader.Read(p)
+	if err != nil {
+		return err
+	}
+	if prog, err := expr.NewBool(result.Text); err != nil {
+		return err
+	} else {
+		scr.SetBoolProgram(prog)
+	}
+	return nil
+}
+
 func (ctrl Controller) ReadExternalFiles(ctx context.Context, wd string) error { //nolint:gocognit
 	for i, phase := range ctrl.Config.Phases {
 		for j, task := range phase.Tasks {
@@ -446,6 +465,9 @@ func (ctrl Controller) ReadExternalFiles(ctx context.Context, wd string) error {
 			if err := ctrl.readScript(task.OutputFile, wd, &task.Output); err != nil {
 				return err
 			}
+			if err := ctrl.readBoolScript(task.WhenFile, wd, &task.When); err != nil {
+				return err
+			}
 			phase.Tasks[j] = task
 		}
 		ctrl.Config.Phases[i] = phase