Bash script - Watch serial-port for specific string, then send back commands

Question

I try to use a bash script to watch the serial-port for a specific string. If this string is shown, some commands should be send back to the connected device. It´s a router I am connected to. It is a router I am connected to and I want to send the commands, after the uboot-menu has appeared.

When using minicom with a ftdi-USB-UART-device directly (no with the script) everything works. "It works" in that case means:

• Bootmenu is shown while a time is counting down, the device is waiting for input until I enter a number or the countdown is over.
• I am able to send a command/enter a number.
• The router "boots" into the selected option. (in my case - the system starts tftp-bootmode where I could input stuff liker server IP and so on...)

Now, when I use the script. The router does not care about inpu also the countdown is not runnig. It just boots directly into the default option. Same behavior when using minicom + /dev/ttyAMA0 on a raspberry pi (ftdi device otherwise works as described).

I am thinking that in my script, there are some parameters missing. Maybe I have to choose special options for stty?

Or do I have to send a special "control character" right at the beginning, for the router to recognize that "there is someone out there who is able to send me some commands"?

I am able to detect the string I am searching for, but as I said before - the router doesn´t recognize the command(s) send:

#!/bin/bash
tty=/dev/ttyUSB0
exec 4<$tty 5>$tty
stty -F $tty 115200 -echo

while [ "${output}" != "Please choose the operation:" ]; do #wait for bootmenu to appear
    read output <&4 
    echo "$output"
done
printf "\t\n  ***** gotcha! *****  \n\n" #bootmenu is showing

echo -e "\x31" >&5 # echo '1' for taking boot option 1
printf "\t\n ***** echo '1' ***** \n\n"

while true; do #just for debugging (was command received?)...
    read output <&4
    echo "$output"
done

#commands for setting Target-IP, TFTP-Server-IP-address should follow here... 

Many thanks in advance :-)

Answer 1

echo -n "1" >&5 did the trick for me. Seems like uboot doesn´t want to get a newline, otherwise it behaves weird.

Thanks a lot for your help!

Here is the "complete" script, maybe it is helpful for someone.

#!/bin/bash
tty=/dev/ttyUSB0
exec 4<$tty 5>$tty
stty -F $tty 115200 -brkint -icrnl -imaxbel iutf8 -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

tftp_client_ip="10.10.30.111"
tftp_server_ip="10.10.30.1"
tftp_file="test.file"

while [ "$firstword" != "Please" ]; do # wait for bootmenu to apear
    read -e output <&4
    firstword=$(echo "$output" | cut -f1 -d" ")
    echo "$output"
done
#printf "\t\n  ***** ***** gotcha! ***** *****  \n\n"
sleep 0.5

# DONT SEND NEWLINEs - otherwise uboot doesn´t recognize commands !!!!!
echo -n "1" >&5 # echo '1' for taking boot option 1
printf "\t\n ***** ***** echo '1' ***** ***** \n\n"
# MUST TO WAIT FOR DELAY - try to fix that by "emulate" RETURN button?
sleep 5

#input TFTP-client IP
for((i=0;i<20;i++)); do
    echo -ne "\b \b" >&5 #erase characters
    sleep 0.05
done
printf  "%s\r" "$tftp_client_ip" >&5

#input TFTP-server IP
for((i=0;i<20;i++)); do
    echo -ne "\b \b" >&5 #erase characters
    sleep 0.05
done
printf  "%s\r" "$tftp_server_ip" >&5

#input TFTP-file
printf  "%s\r" "$tftp_file" >&5

while true; do #just for debugging...
    read -e output <&4
    echo "$output"
done

# router should boot to RAM with "$tftp_file"