kubens: Start implementing stubs

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

internal/cmdutil/interactive.go

@@ -0,0 +1,30 @@
+package env
+
+import (
+	"os"
+	"os/exec"
+
+	"github.com/mattn/go-isatty"
+
+	"github.com/ahmetb/kubectx/internal/env"
+)
+
+// isTerminal determines if given fd is a TTY.
+func isTerminal(fd *os.File) bool {
+	return isatty.IsTerminal(fd.Fd())
+}
+
+// fzfInstalled determines if fzf(1) is in PATH.
+func fzfInstalled() bool {
+	v, _ := exec.LookPath("fzf")
+	if v != "" {
+		return true
+	}
+	return false
+}
+
+// IsInteractiveMode determines if we can do choosing with fzf.
+func IsInteractiveMode(stdout *os.File) bool {
+	v := os.Getenv(env.EnvFZFIgnore)
+	return v == "" && isTerminal(stdout) && fzfInstalled()
+}