Reading only data added since last ready from buffer in golang - go

Question

I am writing a program that uses SSH shells to execute a series of commands, some of which are long-running. The below function successfully reads the output until an end condition is reached, however each time I read the buffer I get all of the output since the command starting running, which I don't really need. Is there a way to only get the data added to the buffer since the last read?
func RunLongSSHCommand(o *bytes.Buffer, stdin io.Writer, command string, end string) bool {
_, err := fmt.Fprintf(stdin, "%s\n", command)
if err != nil {
log.Fatal(err)
}
o.Reset()
log.Info("buffer:", o.String())
log.Println("Command: ", command)
for {
done := false
scanner := bufio.NewScanner(o)
for scanner.Scan() {
fmt.Println(scanner.Text())
if strings.Contains(scanner.Text(), end) {
fmt.Println(scanner.Text())
done = true
break
}
}
if done {
break
}
//o.Reset()
//log.Info("buffer:", o.String())
time.Sleep(3 * time.Second)
}
return true
}
Code that creates buffer:
sess, client := ssh_ftp.SshConnect(dev3)
defer client.Close()
defer sess.Close()
// StdinPipe for commands
stdin, err := sess.StdinPipe()
if err != nil {
log.Fatal(err)
}
// Start remote shell
err = sess.Shell()
if err != nil {
log.Fatal(err)
}
// Uncomment to store output in variable
var b bytes.Buffer
sess.Stdout = &b
sess.Stderr = &b
New problem: The scan of the stdout pipe only breaks with a manual end condition, otherwise it hangs. Is there a way to avoid having a manual end condition?
func RunLongSSHCommand(stdout io.Reader, stdin io.Writer, command string, end string) bool {
_, err := fmt.Fprintf(stdin, "%s\n", command)
if err != nil {
log.Fatal(err)
}
log.Println("Command: ", command)
scanner := bufio.NewScanner(stdout)
print("scanning output")
for scanner.Scan() {
fmt.Println(scanner.Text())
if strings.Contains(scanner.Text(), end) {
fmt.Println("end")
//done = true
break
}
}
print("done")
return true
}
function call :
RunLongSSHCommand(stdout, stdin, command, "Removing Workstation")
pipe declaration.
stdout, err := sess.StdoutPipe()
if err != nil {
log.Fatal(err)
}