Some don't, but $SHELL is generally accurate enough for Bash and Zsh.
You can also check the shell by checking the PID:
ps -p $$
But then you need to do extra output parsing plus, obviously, ps each time you output $PS1. Which is going to be a little overkill for this project since it's only Zsh and Bash you're wanting to capture and you can always have fallback support for those flags when automatic detection fails.
You can also check the shell by checking the PID:
But then you need to do extra output parsing plus, obviously, ps each time you output $PS1. Which is going to be a little overkill for this project since it's only Zsh and Bash you're wanting to capture and you can always have fallback support for those flags when automatic detection fails.