text_formatter: detect tty based on fd

README.md

@@ -87,7 +87,8 @@ func init() {
   // Log as JSON instead of the default ASCII formatter.
   log.SetFormatter(&log.JSONFormatter{})
 
-  // Output to stdout instead of the default stderr, could also be a file.
+  // Output to stdout instead of the default stderr
+  // Can be any io.Writer, see below for File example
   log.SetOutput(os.Stdout)
 
   // Only log the warning severity or above.
@@ -138,7 +139,15 @@ var log = logrus.New()
 func main() {
   // The API for setting attributes is a little different than the package level
   // exported logger. See Godoc.
-  log.Out = os.Stderr
+  log.Out = os.Stdout
+
+  // You could set this to any `io.Writer` such as a file
+  // file, err := os.OpenFile("logrus.log", os.O_CREATE|os.O_WRONLY, 0666)
+  // if err == nil {
+  //  log.Out = file
+  // } else {
+  //  log.Info("Failed to log to file, using default stderr")
+  // }
 
   log.WithFields(logrus.Fields{
     "animal": "walrus",

examples/basic/basic.go

@@ -2,13 +2,22 @@ package main
 
 import (
 	"github.com/Sirupsen/logrus"
+	// "os"
 )
 
 var log = logrus.New()
 
 func init() {
 	log.Formatter = new(logrus.JSONFormatter)
 	log.Formatter = new(logrus.TextFormatter) // default
+
+	// file, err := os.OpenFile("logrus.log", os.O_CREATE|os.O_WRONLY, 0666)
+	// if err == nil {
+	// 	log.Out = file
+	// } else {
+	// 	log.Info("Failed to log to file, using default stderr")
+	// }
+
 	log.Level = logrus.DebugLevel
 }
 

formatter_bench_test.go

@@ -80,11 +80,14 @@ func BenchmarkLargeJSONFormatter(b *testing.B) {
 }
 
 func doBenchmark(b *testing.B, formatter Formatter, fields Fields) {
+	logger := New()
+
 	entry := &Entry{
 		Time:    time.Time{},
 		Level:   InfoLevel,
 		Message: "message",
 		Data:    fields,
+		Logger:  logger,
 	}
 	var d []byte
 	var err error

terminal_appengine.go

@@ -3,6 +3,6 @@
 package logrus
 
 // IsTerminal returns true if stderr's file descriptor is a terminal.
-func IsTerminal() bool {
+func IsTerminal(f io.Writer) bool {
 	return true
 }

terminal_notwindows.go

@@ -9,14 +9,20 @@
 package logrus
 
 import (
+	"io"
+	"os"
 	"syscall"
 	"unsafe"
 )
 
 // IsTerminal returns true if stderr's file descriptor is a terminal.
-func IsTerminal() bool {
-	fd := syscall.Stderr
+func IsTerminal(f io.Writer) bool {
 	var termios Termios
-	_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), ioctlReadTermios, uintptr(unsafe.Pointer(&termios)), 0, 0, 0)
-	return err == 0
+	switch v := f.(type) {
+	case *os.File:
+		_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(v.Fd()), ioctlReadTermios, uintptr(unsafe.Pointer(&termios)), 0, 0, 0)
+		return err == 0
+	default:
+		return false
+	}
 }

terminal_solaris.go

@@ -9,7 +9,13 @@ import (
 )
 
 // IsTerminal returns true if the given file descriptor is a terminal.
-func IsTerminal() bool {
-	_, err := unix.IoctlGetTermios(int(os.Stdout.Fd()), unix.TCGETA)
-	return err == nil
+func IsTerminal(f io.Writer) bool {
+	var termios Termios
+	switch v := f.(type) {
+	case *os.File:
+		_, err := unix.IoctlGetTermios(int(v.Fd()), unix.TCGETA)
+		return err == nil
+	default:
+		return false
+	}
 }

terminal_windows.go

@@ -19,9 +19,13 @@ var (
 )
 
 // IsTerminal returns true if stderr's file descriptor is a terminal.
-func IsTerminal() bool {
-	fd := syscall.Stderr
-	var st uint32
-	r, _, e := syscall.Syscall(procGetConsoleMode.Addr(), 2, uintptr(fd), uintptr(unsafe.Pointer(&st)), 0)
-	return r != 0 && e == 0
+func IsTerminal(f io.Writer) bool {
+	switch v := f.(type) {
+	case *os.File:
+		var st uint32
+		r, _, e := syscall.Syscall(procGetConsoleMode.Addr(), 2, uintptr(v.Fd()), uintptr(unsafe.Pointer(&st)), 0)
+		return r != 0 && e == 0
+	default:
+		return false
+	}
 }

text_formatter.go

@@ -3,9 +3,9 @@ package logrus
 import (
 	"bytes"
 	"fmt"
-	"runtime"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -20,12 +20,10 @@ const (
 
 var (
 	baseTimestamp time.Time
-	isTerminal    bool
 )
 
 func init() {
 	baseTimestamp = time.Now()
-	isTerminal = IsTerminal()
 }
 
 type TextFormatter struct {
@@ -50,6 +48,10 @@ type TextFormatter struct {
 	// that log extremely frequently and don't use the JSON formatter this may not
 	// be desired.
 	DisableSorting bool
+
+	// Whether the logger's out is to a terminal
+	isTerminal   bool
+	terminalOnce sync.Once
 }
 
 func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
@@ -70,8 +72,13 @@ func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
 
 	prefixFieldClashes(entry.Data)
 
-	isColorTerminal := isTerminal && (runtime.GOOS != "windows")
-	isColored := (f.ForceColors || isColorTerminal) && !f.DisableColors
+	f.terminalOnce.Do(func() {
+		if entry.Logger != nil {
+			f.isTerminal = IsTerminal(entry.Logger.Out)
+		}
+	})
+
+	isColored := (f.ForceColors || f.isTerminal) && !f.DisableColors
 
 	timestampFormat := f.TimestampFormat
 	if timestampFormat == "" {