Nimbostratus
MVPv2 First, I found this document that might assist you with your external monitor.
https://community.f5.com/t5/technical-articles/ltm-external-monitors-the-basics/ta-p/277128
Second, do you have a specific reason why an external monitor has been used rather than the build in health monitors? I'm not familiar enough with your bash script or bash in general to know exactly what your script is searching for but maybe we can come up with a health monitor that will work with internal monitors if you can provide exactly what you are sending to the server and what you are expecting back as a valid response?