"But, before the discussion of various shells, a word about why this is relevant. As has been stated, a shell's
basic job is to take commands and either act on them itself, or run other programs to do it. Often, this is
done interactively, with a user issuing commands one at a time, and the shell processing them as they come
in."
"However, almost universally, shells will also accept groups, or "batches", of commands at once. These can be
entered manually, in a single go, on the command line, or you can simply direct your shell to a file, which it
will read, and treat the contents of as commands issued to it. In the DOS world, files such as this were
known as "batch files"; to Unix users, they are "shell scripts". Shell scripts can be, and often are, much more
complex than batch files."
"As I said earlier, there are multiple shells commonly available for Unix systems. The one that new Linux users
most commonly encounter is bash, the "Bourne again shell" -- so named because it was based on the old
Bourne shell, simply called sh. Other shells that new users will frequently encounter are csh (and its improved
brother, tcsh), ksh (and its free version, pdksh), and zsh."
