grc - a Go implementation of the Plan 9 rc shell

`grc` is an interactive and scripting shell for Unix systems, implemented in Go,
with semantics derived from the Plan 9 rc shell.

rc is a list-oriented command language. Variables hold lists, expansion is
structural, and control flow is explicit. grc aims to preserve these semantics
while running on a modern Unix system.

This project is beta-quality but is usable for day-to-day interactive work.

Features
- List-valued variables
- $ expansion with rc semantics
- Free carets and ^ concatenation
- Globbing with literal fallback
- Backquote command substitution
- Functions with dynamic scoping
- Assignments (standalone and prefix)
- Control flow: if/for/while/switch
- Pipes, redirections, background jobs
- $status and $apid
- Interactive REPL with history and prompt
- Execution tracing and plan inspection

Non-goals
grc is not a POSIX shell and does not aim to be compatible with:
- bash / zsh extensions
- POSIX parameter expansion
- brace expansion
- full job control beyond minimal jobs/fg/bg

Installation
  go build ./cmd/grc

Run interactively:
  ./grc

Run a script:
  ./grc < script.rc

Interactive flags
- -n parse and plan only (no execution)
- -p print execution plan
- -x trace executed commands

These flags work in both script and interactive modes.

Documentation
- DESIGN        architecture and execution model
- CONFORMANCE   mapping to Plan 9 rc(1)
- USAGE         practical examples
- BETA          beta status and limitations
- CHANGELOG     notable changes
- LICENSE       license terms

Status
grc is stable enough for daily interactive use, but some rc features are still
in progress.

Do not run as root.