No colors for non-interactive shells

formatter.go

@@ -49,7 +49,7 @@ func (l *Logger) Format(level logLevel, tmpl string, args ...interface{}) string
 	}
 
 	// Find the theme color to use.
-	if l.Config.Colors != NoColor {
+	if interactive && l.Config.Colors != NoColor {
 		var (
 			primary   ThemeColor
 			secondary ThemeColor

golog.go

@@ -1,8 +1,11 @@
 package golog
 
 import (
+	"os"
 	"sync"
 	"text/template"
+
+	"golang.org/x/crypto/ssh/terminal"
 )
 
 // An internal map of named loggers. This allows for GetLogger() to be called
@@ -11,10 +14,16 @@ import (
 var (
 	loggers     map[string]*Logger
 	loggerMutex sync.Mutex
+
+	interactive bool // is an interactive shell
 )
 
 func init() {
 	loggers = map[string]*Logger{}
+
+	// Detect if we're running in an interactive shell, so we can globally
+	// disable colors when redirecting to a log file.
+	interactive = terminal.IsTerminal(int(os.Stdout.Fd()))
 }
 
 // Logger stores the configuration for a named logger instance.

golog_test.go

@@ -3,6 +3,8 @@ package golog
 import "testing"
 
 func TestColors(t *testing.T) {
+	interactive = true // fake an interactive TTY to test color outputs
+
 	log := GetLogger("test")
 
 	// Helper function to emit all the log types.