From DD-WRT Wiki

Contents 1 Access script for Windows 2 Access script for Linux

These scripts provide an easy way for accessing your redboot especially when the bootwait timeout is very short!

[edit] Access script for Windows

download putty.exe to c:\
create a file on c:\ called redboot.txt, with the following content:

^C

create a file on c:\ called redboot.bat with the following content:

rem echo off
:start
rem ------------------------------------------------
ping 192.168.20.81 -n 1 -w 1 >NULL
IF ERRORLEVEL 1 goto start
break

rem start putty
rem ------------------------------------------------
putty.exe telnet://192.168.20.81:9000 -m redboot.txt
exit

for "192.168.20.81" set the ip of the redboot you want to connect.
start the bat file and power on the router. maybe you will have to try it 2 or 3 times

[edit] Access script for Linux

be sure you have putty installed

#!/bin/bash
echo
echo ""
echo "Enter hostname or ip address: "
read host
while true
do
   if eval "ping -c 1 -s 1 $host" > /dev/null; then       
  echo "Router Awake"
       putty telnet://$host 9000 -m redboot.txt
       break
   else
       echo "Waiting for Redboot to boot. Press CTRL + C to quit"
    sleep 1
   fi
done