A stdout/stderr demuxer hook for Logrus

Logrus loggers always output all log levels to a single common output, e.g. stderr. This logrus hook makes it so that logs with a severity below Error are written to stdout while all the important stuff goes to stderr.

You can also use the hook to demux logs to custom IO writers based on severity. Just override the default outputs using the hook's SetOutput(infoLevel, errorLevel io.Writer) method.

Example

Given you have an application that uses a the logrus standard logger similar to this:

import (
    log "github.com/Sirupsen/logrus"
)

func main() {

    log.SetLevel(log.InfoLevel)

    log.Info("A group of penguins emerges from the ocean")

    (...)

The only change required is adding in the hook. Make sure to configure the parent logger before initializing the hook as the latter will inherit it's configuration.

import (
    log "github.com/Sirupsen/logrus"
    "github.com/janeczku/stdemuxerhook"
)

func main() {

    log.SetLevel(log.InfoLevel)
    log.AddHook(stdemuxerhook.New(log.StandardLogger()))

    log.Info("A group of penguins emerges from the ocean") // -> logged to stdout
    log.Panic("A group of polar bears emerges from the ocean") // -> logged to stderr

    (...)

}

Benchmarks

BenchmarkLoggerWithoutHook        300000          4348 ns/op
BenchmarkLoggerWithHook           200000          5436 ns/op