Golang logging
From wikinotes
Logging is a standardized format of writing progress/debug info.
Documentation
log
https://pkg.go.dev/log logfmt flags https://pkg.go.dev/log#pkg-constants
Basics
Go creates a logger that logs to stderr by default.
If you like, you can modify it's logformat.
There are no log-levels by default.// customize default log's logformat log.SetFlags(log.Ldate|log.Ltime|log.Llongfile) // log methods similar to 'fmt.*' methods log.Println("application started") // log message log.Fatalln("application exiting") // os.Exit(1) after logged log.Panicln("application panicked") // panic() after logged
LogLevels
NOTE:
xorm has a really nice logger implementation
Go doesn't provide log-levels, but you can create separate loggers to implement this yourself.
You don't need to do this in every file, log-format flags indicating filepath will use the correct path where it is called from.import "os" import "io/ioutil" import "log" logFmt := log.Ldate|log.Ltime|log.Llongfile InfoLogger := log.New(os.Stderr, "INFO: ", logFmt) ErrorLogger := log.New(os.Stderr, "ERROR: ", logFmt) DebugLogger := log.New(ioutil.Discard, "DEBUG: ", logFmt) // redirects to /dev/nullSample Implementation
package main import "log" import "os" import "io/ioutil" var ( LogDebug *log.Logger LogInfo *log.Logger LogWarn *log.Logger LogError *log.Logger ) func setupLog() { debug_writer := ioutil.Discard info_writer := ioutil.Discard for _, arg := range os.Args[1:] { switch arg { case "-v", "--verbose": info_writer = os.Stderr case "-vv", "--very-verbose": info_writer = os.Stderr debug_writer = os.Stderr } } logFmt := log.Ldate|log.Ltime|log.Llongfile LogDebug = log.New(debug_writer, "DEBUG: ", logFmt) LogInfo = log.New(info_writer, "INFO: ", logFmt) LogWarn = log.New(os.Stderr, "WARN: ", logFmt) LogError = log.New(os.Stderr, "ERROR: ", logFmt) } func main() { setupLog() LogWarn.Println("high memory usage") LogInfo.Println("application started") LogDebug.Println("preparing for error...") LogError.Println("an error was encountered") }Then on your commandline
go build main.go # prints warn/error go build main.go -v # prints info/warn/error go build main.go -vv # prints debug/info/warn/error