174 lines
6.6 KiB
Plaintext
174 lines
6.6 KiB
Plaintext
Scsh is one
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===========
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Scheme shell version 0.1 was released to the Net exactly a year ago today,
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Halloween 1995. We are pleased to release scsh version 0.4 to mark scsh's
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first birthday. The new release has many bug fixes, improvements and new
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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 realised 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 provids 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://swiss-ftp.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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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://swiss-ftp.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://swiss-ftp.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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alt.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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* New in this release
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=====================
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** New system calls.
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select, file locking, full tty device control, ptys, set-file-times,
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process timing, seek & tell. We still don't have signal handlers; with this
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exception, Scsh now has all of Posix.
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** Automatic reaping of exited subprocesses.
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You may wait on a subprocess zero, one, or more times without filling
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up the kernel's process table or generating an error.
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** New delimited-input reader procedures.
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You may read input delimited by a newline character (read-line),
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a blank-line (read-paragraph), or a character from an arbitrary
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set (read-delimited). These procedures have native-code support
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for reading from Unix input sources, and are quite fast.
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** Better support for writing standalone scripts.
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It's much easier to write standalone scripts now. Scripts can use
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the new command-line switches to open dependent modules and load
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dependent source code. Scripts can also be written in the Scheme 48
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module language.
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** Etc.
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Control of I/O buffering policy, better error reporting, bug fixes,
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here-strings, sub-second time precision, ...
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* Thanks
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========
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We thank Travis Broughton, Charlie Conklin, Jin S. Choi, Brian F. Dennis,
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Patrick May, Bill Sommerfeld, Michael Sperber, Steven L. Tamm, Ed Tobin, and
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others for bug reports, bug fixes, and comments that were incorporated into
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this 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, 1995
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