If you check in one of the main threads, everyone has a personal preference. /bin/sh was the first popular shell. Korn shell (ksh) is an enhanced version and Bourne Again Shell (bash) is even more enhanced.

On Solaris, you'll probably use Korn shell and on Linux you'll probably use Bourne Again shell.

ls works because it's in your PATH (type which ls and it'll probably return /bin/ls). Unless you have a script called ls in your current directory, ./ls will not work. If you just type in "./", bash will just tell you that ./ is a directory.

If you type in ./[command], [command] has to be in the current directory. If you just type in [command], then [command] has to be in one of the directories identified by the PATH environment variable.

Carl