start spinner only when fd is terminal (#131)

go.mod

@@ -5,4 +5,5 @@ go 1.14
 require (
 	github.com/fatih/color v1.7.0
 	github.com/mattn/go-colorable v0.1.2 // indirect
+	github.com/mattn/go-isatty v0.0.8
 )

spinner.go

@@ -28,6 +28,7 @@ import (
 	"unicode/utf8"
 
 	"github.com/fatih/color"
+	"github.com/mattn/go-isatty"
 )
 
 // errInvalidColor is returned when attempting to set an invalid color
@@ -271,7 +272,7 @@ func (s *Spinner) Active() bool {
 // Start will start the indicator.
 func (s *Spinner) Start() {
 	s.mu.Lock()
-	if s.active {
+	if s.active || !isRunningInTerminal() {
 		s.mu.Unlock()
 		return
 	}
@@ -439,3 +440,8 @@ func GenerateNumberSequence(length int) []string {
 	}
 	return numSeq
 }
+
+// isRunningInTerminal check if stdout file descriptor is terminal
+func isRunningInTerminal() bool {
+	return isatty.IsTerminal(os.Stdout.Fd())
+}

vendor/modules.txt

@@ -5,6 +5,7 @@ github.com/fatih/color
 ## explicit
 github.com/mattn/go-colorable
 # github.com/mattn/go-isatty v0.0.8
+## explicit
 github.com/mattn/go-isatty
 # golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223
 golang.org/x/sys/unix