If you want the most powerful shell, ksh93 has the most features without doubt. Since David Korn retired, it has been adrift with few updates. The dash shell

If you want the most powerful shell, ksh93 has the most features without doubt. Since David Korn retired, it has been adrift with few updates. The dash shell can be compiled with libedit to implement "set -o vi" (which is also POSIX), and is pleasant to use this way.