Telnetlib - send brk

Patrick Vrijlandt p.vrijlandt at
Tue Oct 16 09:12:47 CEST 2001

"Donnie Miller" <drmiller at>
>    I've been trying the telnetlib library rather than using expect
> scripts as I have done in the past.  I have had success with it up until
> the point where I needed to send a "break" sequence to a server.  I have
> searched all over various lists and google, but have not found
> anything.  Does anyone have any idea of how to do this?

Telnetlib provides no way to send telnet control characters:

IAC  = chr(255) # Interpret As Command
DONT = chr(254) #
DO   = chr(253) #
WONT = chr(252) #
WILL = chr(251) #
SB   = chr(250) # Subnegotiation Begin
GA   = chr(249) # Go Ahead
EL   = chr(248) # Erase Line
EC   = chr(247) # Erase Char
AYT  = chr(246) # Are You There
AO   = chr(245) # Abort Output
IP   = chr(244) # Interrupt Process
BRK  = chr(243) # NVT-Break
DM   = chr(242) # Data Mark
NOP  = chr(241) # No Operation
SE   = chr(240) # Subnegotiation End

So you have to patch the write method, originally:

    def write(self, buffer):
        if IAC in buffer:
            buffer = buffer.replace(IAC, IAC+IAC)
        self.msg("send %s", `buffer`)

so that BRK (and the other telnet commands) also is/are prepended by an IAC

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