tail

README

Go package for tail-ing files

A Go package striving to emulate the features of the BSD tail program.

t, err := tail.TailFile("/var/log/nginx.log", tail.Config{Follow: true})
for line := range t.Lines {
    fmt.Println(line.Text)
}

See API documentation.

Log rotation

Tail comes with full support for truncation/move detection as it is designed to work with log rotation tools.

Installing

go get github.com/ActiveState/tail/...

Documentation

Index

• Variables
• func Cleanup()
• func OpenFile(name string) (file *os.File, err error)
• type Config
• type Line
  • func NewLine(text string) *Line
• type SeekInfo
• type Tail
  • func TailFile(filename string, config Config) (*Tail, error)
  • func (tail *Tail) Stop() error
  • func (tail *Tail) Tell() (offset int64, err error)

Variables

var (
	// DefaultLogger is used when Config.Logger == nil
	DefaultLogger = log.New(os.Stderr, "", log.LstdFlags)
	// DiscardingLogger can be used to disable logging output
	DiscardingLogger = log.New(ioutil.Discard, "", 0)
)

var (
	ErrStop = fmt.Errorf("tail should now stop")
)

Functions

func Cleanup

func Cleanup()

Cleanup removes inotify watches added by the tail package. This function is meant to be invoked from a process's exit handler. Linux kernel may not automatically remove inotify watches after the process exits.

func OpenFile

func OpenFile(name string) (file *os.File, err error)

Types

type Config

type Config struct {
	// File-specifc
	Location    *SeekInfo // Seek to this location before tailing
	ReOpen      bool      // Reopen recreated files (tail -F)
	MustExist   bool      // Fail early if the file does not exist
	Poll        bool      // Poll for file changes instead of using inotify
	RateLimiter *ratelimiter.LeakyBucket

	// Generic IO
	Follow      bool // Continue looking for new lines (tail -f)
	MaxLineSize int  // If non-zero, split longer lines into multiple lines

	// Logger, when nil, is set to tail.DefaultLogger
	// To disable logging: set field to tail.DiscardingLogger
	Logger *log.Logger
}

Config is used to specify how a file must be tailed.

type Line

type Line struct {
	Text string
	Time time.Time
	Err  error // Error from tail
}

func NewLine

func NewLine(text string) *Line

NewLine returns a Line with present time.

type SeekInfo

type SeekInfo struct {
	Offset int64
	Whence int // os.SEEK_*
}

SeekInfo represents arguments to `os.Seek`

type Tail

type Tail struct {
	Filename string
	Lines    chan *Line
	Config

	tomb.Tomb // provides: Done, Kill, Dying
	// contains filtered or unexported fields
}

func TailFile

func TailFile(filename string, config Config) (*Tail, error)

TailFile begins tailing the file. Output stream is made available via the `Tail.Lines` channel. To handle errors during tailing, invoke the `Wait` or `Err` method after finishing reading from the `Lines` channel.

func (*Tail) Stop

func (tail *Tail) Stop() error

Stop stops the tailing activity.

func (*Tail) Tell

func (tail *Tail) Tell() (offset int64, err error)

Return the file's current position, like stdio's ftell(). But this value is not very accurate. it may readed one line in the chan(tail.Lines), so it may lost one line.