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`Mashey' shell repost

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Warren Toomey

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Jan 27, 1999, 3:00:00 AM1/27/99
to
I just found this old netnews article, which is relevant to the
UNIX sheel discussion here recently. I've fixed any OCR mistakes,
but I've left the odd typo intact.

Warren

From: ma...@mips.UUCP (John Mashey)
Newsgroups: net.unix-wizards
Subject: Re: Shell history, true facts, but long
Date: 18 Mar 86 09:05:12 GMT

At Todd Williams' request:

1) In the Beginning, there was the shell, /bin/sh, by Ken Thompson.
I can't remember what version this appeared in, but it was well
before my time, i.e., it sure looked and acted like a shell before
late 73. For more info on the early days, see DMR's paper in the
2nd UNIX BLTJ. Almost nothing was builtin (on purpose), but there
were separate if/goto commands. Goto acted by seeking the file
pointer it shared with its parent shell. For a single-stream
command-line interpreter, most, if not all of the fundamental (in
my opinion) ideas were already present. See reference [1].

2) During the period 1973-1976, lots of people hacked on that shell
in various and sundry ways. USG (UNIX Support Group at Murray Hill)
added some things, and so did we:

3) The "PWB Shell" first appeared in mid-1975. It derived from a
set of requirements and suggestions from me in early 1975 in trying
to do serious shell programming. In mid-1975, the shell acquired
variables, including 3 that were derived from per-process data.
This is where the idea of more generalised path- searching came
in. Some of the existing support commands were beefed up, including
if/else/endif. Most of this work was done by Alan Glasser or Dick
Haight. I ended up taking this over, doing performance analysis,
moving most of the control structure commands into the shell, adding
switch,, while, etc. etc. By this time there was serious shell
programming in massive amounts. This had mostly stabilised by
early/mid 1976, although a few more features were added in early
1977. For various reasons this came to be called the "Mashey shell",
a term I universally abhorred, since it was fundamentally still a
Thompson shell with selected additions and tunings by various of
us, constrained to be mostly upward compatible, leading to some
things that I found less than esthetic. Even less than esthetic
was the title of a later internal Bell Labs course: "Bourne Shell
Programming for Mashey Shell Programmers". See [2] and [3].

4) The Bourne shell work started either in early 1976, or maybe
late 1975. The first version was VERY different; for example, it
used $ as the escape character instead of \. During 1976 there was
a long sequence of modification, dialog, discussion, with various
players in shifting alliances [like the game Diplomacy]. Besides
the Computing Research crew, SRB himself, and me, this is when (as
I recall) Dave Korn started getting involved (as heavy earlier user
and extender of Bourne sh). To summarise, some of the Bourne shell's
fundamentals came from the Thompson shell, but some were new. Some
of the added semantics, and a few pieces of syntax came either from
the PWB shell, or by agreement on what it ought to be, given that
everything was changing anyway. [For example, the environment idea
was a much-needed generalisation of the restricted PWB variables;
this came from DMR, SRB, and I.] This did become the standard shell,
although it took PWBers a while to convert, since they had huge
investments in existing shell procedures. [Not that many had been
written in the standard V6 or earlier shells.] See [4]. As a minor
tidbit, how many 68K programmers out there have cursed the shell's
trapping of memory fault to grow it's storage? I admit to causing
this, having goaded SRB into it by moaning at the speed of the
then-current Bourne shell vs the faster PWB shell.

5) I haven't tracked the exact influences on the C-shell. However,
I believe that certain pieces were at least derived from the PWB
shell's documentation (implementation, if not always exact syntax,
of control cmds): if-the-else- endif, break, breakaw, onintr,
while-end. Ask Bill where he got everything. Finally, note that
there have been a number of other interesting and important shells
around, but I'm tired, and I think more people understand the later
work.

[1] K. Thompson, "The UNIX Command Language", in Structured
Programming, Infotech State of the Art Report, Nicholson House,
Maidenhead, Berkshire, England: Infotech International Ltd (March
1975), 375-384.

Classic Thompson-style paper of maximal insights per word,
incl: "Many familiar computing 'concepts' are missing from
UNIX. Files have no records. There are no access methods.
User programs contain no system buffers. There are no file
types. These concepts fill a much needed gap...

[2] J. R. Mashey, "Using a Command Language as a High-Level
Programming Language", Proc. 2nd Int. Conf on Software Engineering,
IEEE (Oct 13-15, 1976), 169-176.

Includes some usage data; state of the world in PWBland in
mid-1976.

[3] T. A. Dolotta, J. R. Mashey, "Using a Command Language as the
Primary Programming Tool", in Command Language Directions: Proc.
IFIP Working Conference on Command Languauges, Sept 10-14, 1979,
D. Beech, Ed, North- Holland, AMsterdam, 1980.

3 years later; more data; Bourne shell(called here nsh)
included.

[4] S. R. Bourne, "An Introduction to the UNIX Shell", BSTJ 57, No
6, Part 2 (Jul-Aug 1978), 2797-2822.

-john mashey UUCP: {decvax,ucbvax,ihnp4}!decwrl!mips!mash
DDD: 408-720-1700
USPS: MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086

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