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From: wmb@ENG.SUN.COM
Newsgroups: comp.lang.forth
Subject: Re: fsh
Message-ID: <9104121340.AA17242@ucbvax.Berkeley.EDU>
Date: 11 Apr 91 15:34:59 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: wmb%ENG.SUN.COM@SCFVM.GSFC.NASA.GOV
Organization: The Internet
Lines: 59

> Are there any Unix shells that are forth based?  Is there some really
> obvious reason why this would be [impractical|silly|stupid]?  Would anyone
> be interested?  I would think it would be interesting to do, and might
> be faster than the typical "script" approach to developing unix tools....

This idea comes up from time to time.  As far as I know, nobody has taken
a serious stab at implementing it.  I have made some steps in that direction,
as I will describe later, but first let me list some reasons why it may not
be the best thing to do:

        1) The Unix shells are basically programming languages whose
           primitive data types are strings and patterns.  Forth doesn't
           exactly excel in its string-handling capabilities.  Another
           thing that "standard" Forth doesn't have is dynamic memory
           allocation, which is pretty necessary for a lot of the things
           that shells do (e.g. argument wildcard expansion).

        2) The existing Unix shells are pretty adequate for the jobs that
           most people want to do with them.  Sometimes the "quoting" in
           scripts gets a bit hairy, but by and large people can get the
           job done.

        3) The value of many shell scripts is strongly related to the number
           of people who can or will use it.  "fsh" scripts would have a
           pretty limited audience, since the job of propagating a new
           language to a wide audience is very very difficult (Proof:
           literally thousands of programming languages have been invented
           and implemented, but only a handful have more that 100 users,
           and the number of languages that are truly widespread is small
           indeed).

        4) It would take many many hours of work to bring the functionality
           of an "fsh" up to the level of ksh or the latest version of csh.
           What would be the payoff?

Here's what I have done already (and I doubt that I will do much more along
these lines):

        a) You can execute Unix shell commands from within Forth.  The most
           popular commands can be execute directly, simply by typing their
           names.  Other commands must be preceded by "sh ".  I once had a
           mode whereby any unrecognized word was sent to a subshell for
           execution, but I decided that I didn't like that behavior and
           turned it off.

        b) My Forth system has a line editor with interactive history and
           command completion.  This can be used for shell commands too.
           Before ksh came out, I used to use Forth as a front end to csh
           just so I could have the editing functions, but now that we
           have ksh, I just use it directly.

        c) On non-Unix machines, I do use Forth as a shell.  The Atari ST
           and the Macintosh do not come with a standard shell program,
           so I use Forth as a shell when I don't want to use their graphical
           user interface.  The standard OS-9 shell is pretty wimpy (the
           line editing functions are weak), so I use Forth as an editing
           front end for it.

Mitch Bradley, wmb@Eng.Sun.COM