Detect if shell is Bash or other

README.md

Not every shell has the "source" command. For example, in Dash (default for Ubuntu "sh"), the "./" is required in front of the filename.

. ./not_bash.sh

bash_or_zsh.sh

# source it or copy it into your script to avoid invoking a different shell. That's why there's no shebang.
case "$(type declare)" in
  "declare is a shell builtin") echo bash;;
  "declare is a reserved word") echo zsh;;
esac

not_bash.sh

# source it or copy it into your script to avoid invoking a different shell. That's why there's no shebang.
case "$(type declare)" in
  "declare is a shell builtin") ;;
  *) echo "Please use Bash shell"; return 1;;
esac