The Unix shell item

Sep 17 00:22 UTC 2006

Debate and study the differences between Unix shells in this item.

response 2 of 35:

Sep 18 18:57 UTC 2006

C shell is okay as long as you don't try to write scripts in it.

response 4 of 35:

Sep 19 04:01 UTC 2006

The Bourne Shell: /bin/sh (or direct replacement)

The standard 7th Edition shell.  Originally, quite a weird implementation
(it allocated memory by trapping signals and increasing the size of the data
segment instead of just calling malloc, and used preprocessor symbols to
make the code look like a sort of weird variant of ALGOL).  Most modern
versions contrain job control.

The C-Shell: /bin/csh

Developed at Berkeley by Bill Joy.  Descended from the 6th Edition shell
and, while it has some useful features (job control, command history and
associated syntax for its manipulation, file name completion, the use of the
tilde (~) to refer to a user's home directory [default current user]), it
lacks some of the better ones incorporated into the Bourne shell (like the
ability to redirect individual file descriptors.  E.g., for output, you can
either redirect stdout (>) or stdout and stderr together (>&).  In
particular, you cannot easily redirect stderr independently of stdout).  CSH
was designed to have a "C-like" syntax, but I've never really understood
this; it doesn't look particularly C-like to me.  At this stage, mostly
historical.

The Tenex C-Shell: tcsh (non-standard)

This took the C shell, and added to it "Tenex-style" command and filename
completion, and command line editting using vi or emacs style keybindings
(similar to GNU's readline library).  Much more usable than pure C shell
once you get the hang of it.

The Korn Shell: /bin/ksh

Developed at AT&T by David Korn and others.  Derived from the Bourne shell,
but with command recall facilities similar to CSH and many other advanced
features (a command-line editting facility with either emacs or vi modes,
etc).  Supposedly the basis for the POSIX shell, though most systems ship
some sort of Bourne-like shell or derivitive, or the C shell.

The Bourne-again Shell: bash (non-standard)

The GNU reimplementation of the Bourne shell, with lots of new features and
enhacements.  It features command and filename completion, command line
editing, job control, command history and recall with editting, etc.  Pretty
much standard on Linux, much more capable than the original Bourne shell,
and containing pretty much the union of features of all the shells
previously mentioned.  Often criticized for being *too* big and
correspondingly slow.

The 9th Edition Shell: rc (non-standard)

A brand new shell with a syntax reminiscent of the Bourne shell, but far
more regular.  This one actually looks kinda like C; it's far simpler than
any of the others listed here,  but remains powerfl.  It has been adopted as
the standard shell under Plan 9.  Cedes things like job control, history,
command history and command line editing to other programs (under Plan 9,
the window system mostly).

The Extensible shell: es (non-standard)

Based on a Unix-only clone of rc, featuring an embedded Scheme interpreter.
Interesting, but not hugely popular.  A patch to add job control exists.

The Z shell: zsh (non-standard)

Another Bourne-derived shell, quite full-featured.  Nate and Jeff are both
users of zsh; perhaps they can comment further.

I think that's most of the biggies.

response 6 of 35:

Sep 19 21:14 UTC 2006

One feature I remember seeing somewhere, but now can't remember where, 
is a directory stack.  You could 'push' on the current directory, 
change to another one, do some work, then 'pop' back to the original 
one.  It's a feature I've occasionally wished for when I was deep in a 
directory hierarchy.

response 8 of 35:

Sep 20 04:38 UTC 2006

there's also tclsh .

response 10 of 35:

Sep 20 13:10 UTC 2006

Re #6:  pushd and popd are in csh, tcsh, and zsh (but not sh or ksh).

response 12 of 35:

Sep 20 23:24 UTC 2006

Looks like bash has it, too.  What's weird is I thought I'd looked for 
it and failed to find it.  I think I was probably looking at the 
bash(1) manpage instead of the bashbuiltins(1) one.

response 14 of 35:

Sep 21 00:30 UTC 2006

zsh, simple yet powerful. I've been using it ever since my slackware days.

response 16 of 35:

Sep 21 16:44 UTC 2006

No, neither have I.

response 18 of 35:

Sep 21 19:35 UTC 2006

Party of the problem with info pages is that they force a specific usage
model.  It works fine if you "live" within emacs and are used to that style,
but kind of sucks if you want to, say, pipe info through other things, etc.

response 20 of 35:

Mar 22 09:06 UTC 2007

I have been using bash for several years.  Before that I was a tcsh user
for several years because it was better than csh (a few years) by a lot,
and those two supported command aliasing while bash did not at that
time.  Once Bash got command aliasing (and I actually noticed it) I got
tired of making sure my environment had tcsh.

response 22 of 35:

Oct 7 14:34 UTC 2007

Sh and bash use $? for exit status.

response 24 of 35:

Oct 8 13:07 UTC 2007

I don't know the answer, and a little Google searching (which I imagine
you've tried too) didn't turn one up for me.  But since a suspended
command hasn't really "exited", I'm not sure I'd expect suspension to be
reflected in the value of an "exit status" variable anyway.

Does someone else know?

On a somewhat related matter, my searching did turn up a difference
between bash and tcsh in the semantics of the "&&" operator.  If you do

    echo one && sleep 20 && echo two

in bash, and then suspend the sleep with ctrl-z, "$?" is set to 0 and
"echo two" is executed immediately, even though the sleep hasn't exited.
 But if you execute the same sequence in tcsh and suspend with ctrl-z,
"$?" is set to 1 and "echo two" is *not* executed.

Hmmm...  I wonder what the correct POSIX behavior is.