macOS – How to Enable Case Insensitive Tab Completion in Bash

It's not regexp, which is where the confusion comes in. Instead, it uses a system called "globbing" - see:

$ man 7 glob

Instead of [a-z] you need to use [[:lower:]] as such:

$ ls -d [[:lower:]]*

My preferred solution is simply to have the prompt always begin with a newline. That way I always have a blank line between the last command output (except in this case, of course), which feels more natural to me. And the worst case is that instead of overwriting text like you are seeing, I don't get the blank line in between. Unless you try it out for a while and simply can't stand the blank line, I highly recommend it.

PS1='\n\[\033[1;32m\]\u@\h\[\033[0m\]:\[\033[1;34m\]\w\[\033[0m\]\$ '

An additional suggestion, if you're up for it: I also use a multi-line prompt to make my command line as long as possible before wrapping (or scrolling if your terminal or shell is configured for that). I also like to know the history line number. Those two together:

PS1='\n\[\033[1;32m\]\u@\h\[\033[0m\]:\[\033[1;34m\]\w\[\033[0m \!\]\n\$ '

Finally, I also like to get timestamps printed before and after running commands. A simplified version of what I use for that is:

export PROMPT_COMMAND="date +\"%Y-%m-%d %H:%M:%S (%s)\"; trap 'date +\"%Y-%m-%d %H:%M:%S (%s)\"; trap DEBUG' DEBUG"

Head spinning yet? :)