match tail handling of newlines at EOF

Author: sam-kleiner

cmd/gotail/gotail.go

@@ -36,12 +36,36 @@ func main() {
 		os.Exit(1)
 	}
 
-	if n != 0 {
-		config.LineLocation = &tail.SeekInfo{-n + 1, io.SeekEnd}
-	}
-
 	done := make(chan bool)
 	for _, filename := range flag.Args() {
+
+		if n != 0 {
+			file, err := os.Open(filename)
+			if err != nil {
+				fmt.Println(err)
+				return
+			}
+
+			buf := make([]byte, 1)
+			info, err := file.Stat()
+			if err == nil && info.Size() > 0 {
+				_, err = file.ReadAt(buf, info.Size()-1)
+			}
+
+			if err != nil {
+				fmt.Println(err)
+				return
+			}
+
+			// if file ends in newline dont count it against -n
+			offset := int64(1)
+			if string(buf) == "\n" {
+				offset = 0
+			}
+			config.LineLocation = &tail.SeekInfo{-n + offset, io.SeekEnd}
+			file.Close()
+		}
+
 		go tailFile(filename, config, done)
 	}