Add hook to send logs to custom writer #678

hooks/writer/README.md

@@ -0,0 +1,43 @@
+# Writer Hooks for Logrus
+
+Send logs of given levels to any object with `io.Writer` interface.
+
+## Usage
+
+If you want for example send high level logs to `Stderr` and
+logs of  normal execution to `Stdout`, you could do it like this:
+
+```go
+package main
+
+import (
+	"io/ioutil"
+	"os"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/writer"
+)
+
+func main() {
+	log.SetOutput(ioutil.Discard) // Send all logs to nowhere by default
+
+	log.AddHook(&writer.Hook{ // Send logs with level higher than warning to stderr
+		Writer: os.Stderr,
+		LogLevels: []log.Level{
+			log.PanicLevel,
+			log.FatalLevel,
+			log.ErrorLevel,
+			log.WarnLevel,
+		},
+	})
+	log.AddHook(&writer.Hook{ // Send info and debug logs to stdout
+		Writer: os.Stdout,
+		LogLevels: []log.Level{
+			log.InfoLevel,
+			log.DebugLevel,
+		},
+	})
+	log.Info("This will go to stdout")
+	log.Warn("This will go to stderr")
+}
+```