201 lines
7.6 KiB
Plaintext
201 lines
7.6 KiB
Plaintext
Scsh is two
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===========
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Scheme shell version 0.1 was released to the Net exactly two years ago
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today, Halloween 1994. We are pleased to release scsh version 0.4.3 to
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mark scsh's second birthday. The new release has many bug fixes,
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improvements and new features.
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The text below gives a general description of scsh, instructions for
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obtaining it, pointers to discussion forums, and a description of the
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new features in release 0.4. To read this document with emacs outline
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mode, say M-x outline-mode.
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* What is scsh
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==============
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Scsh is a broad-spectrum systems-programming environment for Unix embedded
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in R4RS Scheme.
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** Scsh as a scripting language
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-------------------------------
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Scsh has a high-level process notation for doing shell-script like tasks:
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running programs, establishing pipelines and I/O redirection. For example, the
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shell pipeline
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gunzip < paper.tex.gz | detex | spell | lpr -Ppulp &
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would be written in scsh as
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(& (| (gunzip) (detex) (spell) (lpr -Ppulp)) ; Background a pipeline
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(< paper.tex.gz)) ; with this redirection
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Scsh embeds this process notation within a full Scheme implementation.
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The process notation is realized as a set of macro definitions, and is
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carefully designed to allow full integration with standard Scheme code.
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Scsh isn't Scheme-like; it is Scheme.
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At the scripting level, scsh also has an Awk design, also implemented
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as a macro that can be embedded inside general Scheme code.
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** Scsh as a systems-programming language
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-----------------------------------------
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Scsh additionally provides the low-level access to the operating system
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normally associated with C. With the exception of signal handlers, the current
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release provides full access to Posix, plus important non-Posix extensions,
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such as complete sockets support. "Complete Posix" means: fork, exec & wait,
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sockets, full read, write, open & close, seek & tell, complete file-system
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access, including stat, chmod/chgrp/chown, symlink, FIFO & directory access,
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tty & pty support, file locking, pipes, select, file-name pattern-matching,
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time & date, environment variables, and more.
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In brief, you can now write Unix systems programs in Scheme instead of C.
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For example, we have implemented an extensible HTTP server at MIT entirely
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in scsh.
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As important as full access to the OS is the manner in which it is provided.
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Scsh integrates the OS support into Scheme in a manner which respects the
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general structure of the language. The details of the design are discussed
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in a joint MIT Lab for Computer Science/University of Hong Kong technical
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report, "A Scheme Shell," also to appear in a revised format in the *Journal
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of Lisp and Symbolic Computation." This paper is also available by ftp:
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ftp://ftp-swiss.ai.mit.edu/pub/su/scsh/scsh-paper.ps
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** Scsh is a portable programming environment
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---------------------------------------------
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Scsh is designed for portability. It is implemented on top of Scheme 48,
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a byte-code-interpreter Scheme implementation. The Scheme 48 virtual machine
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can be compiled on any system with a C compiler; the rest of Scheme 48 is
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machine-independent across 32-bit processors. Scsh's OS interface is
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also quite portable, providing a consistent interface across different
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Unix platforms. We currently have scsh implementations for
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AIX,
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CXUX,
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FreeBSD,
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HP-UX,
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IRIX,
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Linux,
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NetBSD,
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NeXTSTEP,
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Solaris,
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SunOS,
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Ultrix
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Scsh code should run without change across these systems.
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Porting to new platforms is usually not difficult.
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* Obtaining and installing scsh
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===============================
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You can get a copy of scsh via anonymous ftp, from
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ftp://ftp-swiss.ai.mit.edu/pub/su/scsh/scsh.tar.gz
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The tar file includes a detailed manual and a paper describing
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the design of the system.
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For the lazily curious, we also have the manual separately available as
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ftp://ftp-swiss.ai.mit.edu/pub/su/scsh/scsh-manual.ps
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Just click 'n view.
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You *should* be able to build scsh on the standard platforms with exactly five
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commands: gunzip, tar, cd, ./configure, and make. The configure script figures
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out the special flags and switches needed to make the build work (thanks to
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the GNU project for the autoconfig tool that makes this possible).
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After doing the make, you can start up a Scheme shell and try it out
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by saying
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./scshvm -o ./scshvm -i ./scsh/scsh.image
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See the manual for full details on the command-line switches.
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If it's harder than this, and your system is standard, we'd like to know
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about it.
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* Getting in touch
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==================
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There are two main ways to join in scsh-related discussion: the mailing-list
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scsh@martigny.ai.mit.edu
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and the netnews group
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comp.lang.scheme.scsh
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These two forums are exactly equivalent, being bi-directionally gatewayed
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at MIT.
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Bugs can be reported to
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scsh-bugs@martigny.ai.mit.edu
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If you do not receive the alt netnews hierarchy, or wish to join the mailing
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list for other reasons, send mail to
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scsh-request@martigny.ai.mit.edu
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* The World-Wide What?
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======================
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We even have one of those URL things:
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http://www-swiss.ai.mit.edu/scsh/
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* New in this release
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=====================
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** Signal handlers
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We finally have signal handlers. Go wild.
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** Static heap linker
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The static heap linker converts a Scheme 48 bytecode image as
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embodied in a .image file to a C representation. This C
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code is then compiled and linked in with a virtual machine. One
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pleasant side effect of this is reduced startup times and heap sizes.
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Another good thing is that immutable parts of the image can be shared
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between processes. see the script scsh/static.scm
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** Last few bits of Posix
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Scheme bindings for isatty(), ttyname(), ctermid(), and fcntl().
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** Regular expression compilation
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- MAKE-REGEXP now actually does something useful.
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- AWK has been modified to use it, precompiling all of its
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patterns outside the main loop.
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- Unfortunately, things are still pretty slow. We'll work on it.
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** New meta-arg second-line syntax
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Simpler grammar.
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** New -s<fdes> command line switch
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Scripts can be read from stdin or other open file descriptors.
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** Starting up programs with the "-e <entry-point>" command-line
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switch and with the (DUMP-SCSH-PROGRAM <file-name> <entry-point>)
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are now equivalent in that both pass a list of command-line arguments
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that includes the program name. The two start-up methods were not
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the same in the previous release. NOTE: THIS IS A BACKWARDS-INCOMPATIBLE
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CHANGE IN DUMP-SCSH-PROGRAM FROM THE PREVIOUS RELEASE.
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** Etc.
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Solaris 2 on i386 support, AIX 4 support, HP-UX now uses dld for
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faster loading, a few small networking bug fixs, better error
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reporting, bug fixes, more efficient handling of closing unrevealed
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file descriptors at exec() with CLOEXEC, ...
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* Thanks
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========
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We would like to thank Michael Becker, Glenn Barry, Travis Broughton,
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Robert E. Brown, Charlie Conklin, Franklin Chen, Jin S. Choi, Douglas
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S. J. De Couto, Brian F. Dennis, Sean Doran, Kevin Esler, Lutz Euler,
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Lewis Girod, Dan Hagerty, Rolf-Thomas Happe, David Hull, Steven L.
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Jenkins, Patrick May, Richard Kelsey, Jay Nietling, Tod Olson,
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Jonathan Rees, Michel Schinz, Cotton Seed, Bill Sommerfeld, Michael
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Sperber, Steven L. Tamm, Ed Tobin, Victor Zandy, and others for bug
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reports, bug fixes, and comments that were incorporated into this
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release. We really appreciate their help, particularly in the task of
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porting scsh to new platforms.
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We'd like to thank everyone else for their patience; this release seemed like
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a long time coming.
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Brought to you by the Scheme Underground scsh team. Go forth and write
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elegant systems programs.
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-Olin Shivers & Brian Carlstrom
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Cambridge
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31 October, 1996
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