Improved bash code styling

[AlexSkrypnyk]

I suggest following https://google.github.io/styleguide/shell.xml#Variable_Names

Currently, global constants, env variables and one-time variables that can be local are using the same UPPERCASE format. Would be nice to have local vars as lowercase.

Also, lots of functionality is executed in global context without being split into functions. I suggest moving some functionality into functions to make contribution and debugging easy.