Package golog is a logging package that I'd like to be initially in Go's (Golang) standard library: it's a simple logging tool with levels and different outputs for info and error messages.

TL;DR

golog.Infoln("Started")
// Output: [INF] main: 2018/11/26 16:57:49 main.go:61: Started
golog.Errorf("An error %v occured: %v\n", mycode, mymsg)
// Output: [ERR] main: 2018/11/26 16:57:50 main.go:62: An error 01 occured: just err

Package "golog" provides loggerGlobal and Logger (custom logger) which support:

1. Levels:

• trace (Trace(), Tracef(), Traceln());
• debug (Debug(), Debugf(), Debugln());
• info (Info(), Infof(), Infoln(), Print(), Printf(), Println());
• warning (Warning(), Warningf(), Warningln());
• error (Error(), Errorf(), Errorln());
• critical (Critical(), Criticalf(), Criticalln());
• panic (Panic(), Panicf(), Panicln());
• fatal (Fatal(), Fatalf(), Fatalln()).

2. Different outputs:

• for info-like messages (Trace, Debug, Info, Warning) - os.Stdout by default;
• for error-like messages (Error, Critical, Panic, Fatal) - os.Stderr by default.

You can set:

1. logging level golog.SetLevel(golog.LevelInfo) (LevelTrace, LevelDebug, LevelInfo, LevelWarning, LevelError, LevelCritical). In this case, messages from the lower level will be omitted - LevelTrace by default;
2. custom prefix golog.SetPrefix("myapp:") additionally to level prefixes ("main: " by default);
3. output io.Writer interfaces golog.SetOutput(myOutLogWriter, myErrLogWriter):

• l.outWriter for Trace-Warning (os.Stdout by default);
• l.errWriter for Error-Fatal (os.Stderr by default).

4. flags golog.SetFlags(log.Ltime | log.Lshortfile) similar to "log" from standard library for time and file information ("2018/11/26 16:57:49 golog.go:61" by default).

You can change level prefixes directly (defaults are TRC, DBG, INF, ERR, CRT, PNC, FTL) but don't do it if you don't need it really.

Also, "golog" uses same position conventions as "log": all prefixes are placed before time info.

So, common message using golog.Infoln("Started") will be:

[INF] main: 2018/11/26 16:57:49 main.go:61: Started

Tip: in common usage if you don't know which messages you should use, use Infoln() and Errorln().

Enjoy!