schemesh

Fusion between a Unix shell and a Lisp REPL

Current status: ALPHA.

Some features work, many others are incomplete or missing.

Use at your own risk!

Schemesh is a fusion between a Unix shell and a Lisp REPL - Chez Scheme REPL, to be exact.

It supports interactive line editing and familiar Unix shell syntax for starting commands, including redirections, pipelines, job concatenation with && ||, groups surrounded by { }, and managing foreground/background jobs.

For scripting and serious programming, it completely replaces the slow, clumsy scripting language of a traditional shell (yes, the author has opinions) with a full-featured Lisp REPL, backed by a fast open-source Lisp compiler that generates highly optimized native code.

This means you can use Lisp control structures, loops and functions such as

(if (some_expression arg1 (sub_expression2))
  (then_run_here)
  (otherwise_run_here))

instead of typical shell syntax, which is error prone as it's based on string expansion and splitting, and geared toward command execution, as for example:

if some_command "$arg1" "$(sub_command)"
then
  then_run_this_command
else
  else_run_this_command
fi

Switching between shell syntax and Lisp syntax is extremely simple, and can be done basically everywhere:

• open parenthesis ( temporarily switches to Lisp syntax until the corresponding closed parenthesis )

• open brace i.e. { temporarily switches to shell syntax until the corresponding closed brace i.e. }

• open bracked i.e. [ starts a new sub-form in current syntax until the corresponding closed bracket i.e. ] If found in Lisp syntax, it is equivalent to ( If found in shell syntax, it is similar to { with the difference that commands will be executed in a subshell.

• the directives #!scheme #!chezscheme and #!r6rs temporarily switch to Lisp syntax (with the appropriate flavor) until the end of current list or group inside ( ), [ ] or { }. If entered at top level, they change the default syntax until another directive is entered at top level.

• the directive #!shell temporarily switches to shell syntax until the end of current list or group inside ( ), [ ] or { }. If entered at top level, it changes the default syntax until another directive is entered at top level.

Examples:

find (lisp-function-returning-some-path) -type f | grep ^lib | wc -l

(define job {ls -l | grep some-file-name})
(sh-start job)
(sh-fg job)

Schemesh can be used as:

• a replacement for traditional interactive Unix shell, as for example bash/ksh/zsh etc.

• a Unix shell scriptable in Lisp

• a Lisp REPL with additional syntax and functions to start, redirect and manage Unix processes

• a Lisp library for starting, redirecting and managing Unix processes