shell wrapper to restart script based on its output - regex

Question

I've had a bit of shell scripting practice reading piped input from other programs, but am unsure how to approach this problem.
THE BACKSTORY
A program robinbotter whose internals I can't really fix/modify takes its input from files equities.sym and blacklist.sym, each simple text files containing one ticker symbol per line.
When it runs okay, its output produces:
...
Downloading instruments: [ AFL KELYB LFUS ]
...
When it breaks due to internal bugs,
...
Downloading instruments: [ AFL KELYB LFUS LNVGY
and halts there, with no further output, yielding exit code 0 like in the okay case (unfortunately).
The ticker symbols are printed out with slight delay--no newlines in between--while the program is processing them.
When it hits LNVGY or unpredictably any other many possibilities, somehow it can't handle or at least skip them, instead crashing with no proper exception nor error code.
THE QUESTION
I'm trying to write a minimalistic wrapper script in BASH (eg. retryRB.sh ./robinbotter) which:
Somehow monitors the live unbuffered output of robinbotter, using a regex or other method to detect when output of a line containing "Downloading instruments: [ " doesn't end with "]" before the program ends. In which case:
Take the last symbol printed out (eg. LNVGY) which crashes the program, and append it to the bottom of file blacklist.sym. Like with
echo $lastSymbol >> blacklist.sym
Restart the program robinbotter, retaining its original command-line parameters: $#
I am familiar with tools like awk and sed, and would be open to building a short solution in Ruby if Bash doesn't cut it.

Answer 1

Here you have a Bash version of a code that imitates what your binary does.
then you have a wrapper which logs when the apps successfully completes, and also, when it fails. On failure, it also appends the last item printed, as you can see in the images below ( in this case Im hard-coding a failure on Bomb! and Boom! but you get the idea):
main.sh
#!/bin/bash
some=('Pera' 'Manzana' 'Frutilla' 'Durazno' 'Banana' 'Lechuga' 'Sandia' 'Papa' 'Melon' 'Milanesa' 'Bomb!' 'Boom!')
printf 'Downloading instruments: [ '
for (( i=1 ; i < 5 ; i++ )) {
item=${some[$( shuf -i 0-$(( ${#some[#]} - 1 )) -n 1 )]}
printf "$item"
[[ $item == 'Bomb!' || $item == "Boom!" ]] && exit || printf "$item"
[[ $i -lt 4 ]] && printf ' '
}
printf ' ]'
wrapper.sh
#!/bin/bash
while :
do
res=$( ./main.sh )
[[ ! "$res" =~ \[[^]]*\] ]] && printf "Failure : ${res##*[\[ ]}" || printf "Success"
printf '\n'
sleep 1
done
You can test these scripts and then put your binary in place of main.sh.
Regards!