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