Scsh is one
Scheme shell version 0.1 was released to the Net exactly a year ago today,
Halloween 1995. We are pleased to release scsh version 0.4 to mark scsh's
first birthday. The new release has many bug fixes, improvements and new
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
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
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:
** 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
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
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
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).
If it's harder than this, and your system is standard, we'd like to know
* Getting in touch
There are two main ways to join in scsh-related discussion: the mailing-list
and the netnews group
These two forums are exactly equivalent, being bi-directionally gatewayed
Bugs can be reported to
If you do not receive the alt netnews hierarchy, or wish to join the mailing
list for other reasons, send mail to
* New in this release
** New system calls.
select, file locking, full tty device control, ptys, set-file-times,
process timing, seek & tell. We still don't have signal handlers; with this
exception, Scsh now has all of Posix.
** Automatic reaping of exited subprocesses.
You may wait on a subprocess zero, one, or more times without filling
up the kernel's process table or generating an error.
** New delimited-input reader procedures.
You may read input delimited by a newline character (read-line),
a blank-line (read-paragraph), or a character from an arbitrary
set (read-delimited). These procedures have native-code support
for reading from Unix input sources, and are quite fast.
** Better support for writing standalone scripts.
It's much easier to write standalone scripts now. Scripts can use
the new command-line switches to open dependent modules and load
dependent source code. Scripts can also be written in the Scheme 48
Control of I/O buffering policy, better error reporting, bug fixes,
here-strings, sub-second time precision, ...
We thank Travis Broughton, Charlie Conklin, Jin S. Choi, Brian F. Dennis,
Patrick May, Bill Sommerfeld, Michael Sperber, Steven L. Tamm, Ed Tobin, 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
31 October, 1995