github.com/u-root/u-root@v7.0.1-0.20200915234505-ad7babab0a8e+incompatible/cmds/core/elvish/util/log.go (about)

     1  package util
     2  
     3  import (
     4  	"io"
     5  	"io/ioutil"
     6  	"log"
     7  	"os"
     8  )
     9  
    10  var (
    11  	out io.Writer = ioutil.Discard
    12  	// If out is set by SetOutputFile, outFile is set and keeps the same value
    13  	// as out. Otherwise, outFile is nil.
    14  	outFile *os.File
    15  	loggers []*log.Logger
    16  )
    17  
    18  // GetLogger gets a logger with a prefix.
    19  func GetLogger(prefix string) *log.Logger {
    20  	logger := log.New(out, prefix, log.LstdFlags)
    21  	loggers = append(loggers, logger)
    22  	return logger
    23  }
    24  
    25  // SetOutput redirects the output of all loggers obtained with GetLogger to the
    26  // new io.Writer. If the old output was a file opened by SetOutputFile, it is
    27  // closed.
    28  func SetOutput(newout io.Writer) {
    29  	if outFile != nil {
    30  		outFile.Close()
    31  		outFile = nil
    32  	}
    33  	out = newout
    34  	outFile = nil
    35  	for _, logger := range loggers {
    36  		logger.SetOutput(out)
    37  	}
    38  }
    39  
    40  // SetOutputFile redirects the output of all loggers obtained with GetLogger to
    41  // the named file. If the old output was a file opened by SetOutputFile, it is
    42  // closed. The new file is truncated. SetOutFile("") is equivalent to
    43  // SetOutput(ioutil.Discard).
    44  func SetOutputFile(fname string) error {
    45  	if fname == "" {
    46  		SetOutput(ioutil.Discard)
    47  		return nil
    48  	}
    49  	file, err := os.OpenFile(fname, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
    50  	if err != nil {
    51  		return err
    52  	}
    53  	SetOutput(file)
    54  	outFile = file
    55  	return nil
    56  }