add SetupStdLogger to initialize std global logger with lgr

README.md

@@ -88,8 +88,12 @@ _Note: formatter (predefined or custom) adds measurable overhead - the cost will
 
 _`level` parameter is optional, if defined (non-empty) will enforce the level._
 
+- `lgr.SetupStdLogger(opts ...Option)` initializes std global logger (`log.std`) with lgr logger and given options. 
+All standard methods like `log.Print`, `log.Println`, `log.Fatal` and so on will be forwarder to lgr.
+
 ### global logger
 
 Users **should avoid** global logger and pass the concrete logger as a dependency. However, in some cases a global logger may be needed, for example migration from stdlib `log` to `lgr`. For such cases `log "github.com/go-pkgz/lgr"` can be imported instead of `log` package.
 
 Global logger provides `lgr.Printf`, `lgr.Print` and `lgr.Fatalf` functions. User can customize the logger by calling `lgr.Setup(options ...)`. The instance of this logger can be retrieved with `lgr.Default()`
+

adaptor.go

@@ -29,3 +29,12 @@ func ToWriter(l L, level string) *Writer {
 func ToStdLogger(l L, level string) *log.Logger {
 	return log.New(ToWriter(l, level), "", 0)
 }
+
+// SetupStdLogger makes the default std logger with lgr.L
+func SetupStdLogger(opts ...Option) {
+	logOpts := append([]Option{CallerDepth(3)}, opts...) // skip 3 more frames to compensate stdlog calls
+	l := New(logOpts...)
+	log.SetOutput(ToWriter(l, ""))
+	log.SetPrefix("")
+	log.SetFlags(0)
+}

adaptor_test.go

@@ -2,6 +2,7 @@ package lgr
 
 import (
 	"bytes"
+	"log"
 	"testing"
 	"time"
 
@@ -53,3 +54,18 @@ func TestAdaptor_ToStdLogger(t *testing.T) {
 	wr.Printf("xxx %s", "yyy")
 	assert.Equal(t, "2018/01/07 13:02:34.000 WARN  xxx yyy\n", rout.String())
 }
+
+func TestSetupStdLogger(t *testing.T) {
+	rout, rerr := bytes.NewBuffer([]byte{}), bytes.NewBuffer([]byte{})
+	SetupStdLogger(Out(rout), Err(rerr), Format(WithMsec))
+	log.Print("something\n")
+	assert.Contains(t, rout.String(), " INFO  something\n")
+	rout.Reset()
+
+	log.Print("[WARN] something\n")
+	assert.Contains(t, rout.String(), " WARN  something\n")
+	rout.Reset()
+
+	log.Print("[DEBUG] something\n")
+	assert.Empty(t, rout.String())
+}