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nshell

A modern, fish-inspired interactive shell written in Common Lisp.

nshell is an interactive shell that puts the interactive experience first: real-time syntax highlighting, history-aware autosuggestions, fish-style abbreviations, and a fast, context-aware completion engine — all built on a clean, test-driven Common Lisp core and a reproducible Nix build.

Status: development preview (0.4.x)

The interactive editor and core pipeline execution are solid and heavily tested. The shell language is a growing subset of POSIX/fish semantics — see the roadmap for what is and isn't supported yet. nshell is usable as a daily interactive shell for common workflows; it is not a script-compatible /bin/sh replacement.

Highlights

  • Syntax highlighting as you type — a command that would fail with command not found is red before you run it, existing paths are underlined, and strings, variables, keywords, and operators each get their own color.
  • Autosuggestions from your history, fish-style, accepted with → / Ctrl-F.
  • Abbreviations (abbr) that expand inline as you type — keep your muscle memory, type less.
  • Context-aware completion — a knowledge base of commands and flags plus filesystem completion, git branches, environment variables, and directory-only completion for cd, in a colored candidate menu with common-prefix Tab extension.
  • Rich line editing — Emacs keybindings, kill-ring and yank, multi-level undo/redo, multiline editing, and a Ctrl-R history picker that lists matches under the prompt.
  • Vi key bindings (optional, NSHELL_VI_MODE=1) — normal-mode motions, counts, operators (dd, cw, …), visual selection, and insert/append.
  • Themes — one named palette drives the prompt, the highlighter, and the completion menu; ten presets ship with the shell, theme use switches live, and colors downsample to 256- or 16-color terminals.
  • A prompt that reports — working directory, git branch and dirty marker, a prompt character that turns red after a failure, and, on the right, the failing exit code plus the duration of anything slower than a second.
  • Job control — background jobs (&), jobs, fg, bg, disown.
  • Pipelines and redirection — |, >, >>, <, <<, <<<, logical && / ||, and command sequencing.
  • Control flow and functions — if, for, while, switch, begin/end, and user-defined functions.
  • History expansion — !!, !$, !-N, !?text?, and !prefix, with quoted and backslash-escaped exclamation marks kept literal.
  • External editing — Alt-E opens the current line with the configured editor and returns the edited buffer to the prompt.
  • Reproducible build — a dumped SBCL image and its process-launch helper via Nix; nix run and you're in.

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