[ Thanks to Devin M.
Ash for this link. ]
“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.”