在Go中更新日志文件时读取它们

Question

I'm trying to parse some log files as they're being written in Go but I'm not sure how I would accomplish this without rereading the file again and again while checking for changes.

I'd like to be able to read to EOF, wait until the next line is written and read to EOF again, etc. It feels a bit like how tail -f looks.

Answer 1

I have written a Go package -- github.com/ActiveState/tail -- to do exactly this.

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

...

Quoting kostix's answer:

in real life files might be truncated, replaced or renamed (because that's what tools like logrotate are supposed to do).

If a file gets truncated, it will automatically be re-opened. To support re-opening renamed files (due to logrotate, etc.), you can set Config.ReOpen, viz.:

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

Config.ReOpen is analogous to tail -F (capital F):

 -F      The -F option implies the -f option, but tail will also check to see if the file being followed has been
         renamed or rotated.  The file is closed and reopened when tail detects that the filename being read from
         has a new inode number.  The -F option is ignored if reading from standard input rather than a file.