Add --status flag to check is a task is up-to-date

Closes #81

README.md

@@ -300,6 +300,9 @@ generate-files:
 You can use `--force` or `-f` if you want to force a task to run even when
 up-to-date.
 
+Also, `task --status [tasks]...` will exit with non-zero exit code if any of
+the tasks is not up-to-date.
+
 ### Variables
 
 When doing interpolation of variables, Task will look for the below.

cmd/task/task.go

@@ -50,6 +50,7 @@ func main() {
 		versionFlag bool
 		init        bool
 		list        bool
+		status      bool
 		force       bool
 		watch       bool
 		verbose     bool
@@ -60,6 +61,7 @@ func main() {
 	pflag.BoolVar(&versionFlag, "version", false, "show Task version")
 	pflag.BoolVarP(&init, "init", "i", false, "creates a new Taskfile.yml in the current folder")
 	pflag.BoolVarP(&list, "list", "l", false, "lists tasks with description of current Taskfile")
+	pflag.BoolVar(&status, "status", false, "exits with non-zero exit code if any of the given tasks is not up-to-date")
 	pflag.BoolVarP(&force, "force", "f", false, "forces execution even when the task is up-to-date")
 	pflag.BoolVarP(&watch, "watch", "w", false, "enables watch of the given task")
 	pflag.BoolVarP(&verbose, "verbose", "v", false, "enables verbose mode")
@@ -116,6 +118,13 @@ func main() {
 		log.Fatal(err)
 	}
 
+	if status {
+		if err = e.Status(calls...); err != nil {
+			log.Fatal(err)
+		}
+		return
+	}
+
 	if err := e.Run(calls...); err != nil {
 		log.Fatal(err)
 	}

status.go

@@ -8,6 +8,24 @@ import (
 	"github.com/go-task/task/internal/status"
 )
 
+// Status returns an error if any the of given tasks is not up-to-date
+func (e *Executor) Status(calls ...Call) error {
+	for _, call := range calls {
+		t, ok := e.Tasks[call.Task]
+		if !ok {
+			return &taskNotFoundError{taskName: call.Task}
+		}
+		isUpToDate, err := t.isUpToDate(e.Context)
+		if err != nil {
+			return err
+		}
+		if !isUpToDate {
+			return fmt.Errorf(`task: Task "%s" is not up-to-date`, t.Task)
+		}
+	}
+	return nil
+}
+
 func (t *Task) isUpToDate(ctx context.Context) (bool, error) {
 	if len(t.Status) > 0 {
 		return t.isUpToDateStatus(ctx)