gleshell#

A structured-data shell written in Gleam, inspired by Nushell.

Instead of piping opaque text between programs, gleshell pipelines pass typed values: strings, numbers, lists, records, and tables. Built-in commands like ls, where, and select work on that structure.

~/code/gleshell on  main
 ❯ ls | where type == file | select name size | first 5
╭──────┬──────╮
│ name │ size │
├──────┼──────┤
│ …    │ …    │
╰──────┴──────╯

The interactive prompt is zero-config and Starship-inspired: full path with ~, optional git branch (read from .git, no external tools), and a Nerd Font shell icon () before the ❯ character (which turns red after a non-zero exit). Install a Nerd Font so the glyphs render (flake: nix profile install .#nerd-fonts, or put nerd-fonts.symbols-only in your system/fonts packages; the devenv shell already includes it).

Quick start#

Requires Gleam and Erlang (or use Nix):

# install a self-contained `gle` (Erlang shipment in the Nix store — no repo checkout)
nix profile install .
gle -c 'ls | first 3'

# one-shot without installing
nix run . -- -c 'ls | first 3'

# dev shell (source tree; gleam, erlang, rebar3)
# Preferred: direnv auto-loads the flake shell (see .envrc). Once:
#   direnv allow
# then cd into the repo (nushell needs a direnv pre_prompt hook; see below).
# Manual alternative — bare `nix develop` fails under pure flake eval:
nix develop --no-pure-eval
gleam run                 # interactive REPL
gleam run -- -c 'ls | first 3'
gleam test

direnv#

This repo ships a .envrc that runs use flake . --no-pure-eval so devenv can see the real project directory (pure flake eval cannot).

1. Install direnv and hook it into your shell (nushell, bash, zsh, …).
2. From the repo root: direnv allow
3. Open a new shell (or cd .) — you should see the devenv enter message and have gleam on PATH without running nix develop.

Bare nix develop still needs --no-pure-eval for the same reason; with direnv you usually do not need nix develop at all.

REPL editing#

On a TTY the interactive REPL uses a raw-mode line editor with Nushell-style syntax highlighting as you type (commands cyan, strings green, numbers purple, pipes purple, flags blue, variables purple, …).

History is persisted under the user cache as gleshell-history/lines. Non-TTY input falls back to Erlang’s edlin/get_until path.

Examples#

# list files as a table, filter, project columns
ls | where type == file | select name size
ls | find toml md
echo [moe larry curly] | find l

# ranges and list ops
range 10 | reverse | first 3
range 5 | length

# records and JSON
echo {name: "gleshell", cool: true}
echo "{\"a\": 1}" | from json | get a
open data.json | get users | first
range 3 | to json

# variables
let n = range 3 | length
echo $n

# process environment (Nushell-style)
$env.HOME
$env | get PATH
$env.MY_VAR = hello
echo $env.MY_VAR

# external programs (stdout captured as a string)
^uname -a
which ls
which -a ls

Language sketch#

Built-ins#

Filesystem: ls, cd, pwd, cat, open, save

Table/list: where/filter, find, select, get, first, last, take, skip, sort-by, reverse, length, columns, table, flatten, uniq, wrap, unwrap, keys, values

Data: echo, range, lines, to/from (subcommand json), type, describe, env, sys, which, help, about, exit

Pager: less — builtin color-aware pager for pipeline input or files (ls | less, less README.md). ANSI from tables and external tools is kept; short output is printed without an interactive session. Interactive keys include live / search (case-insensitive, finds as you type) and n/N next/previous match. ^less still runs the external binary.

Unknown command names fall through to external executables on PATH.

Layout#

src/
  gleshell.gleam          # entry + REPL
  gleshell_ffi.erl        # line editor (Ctrl+R), cwd, process spawn
  gleshell/
    value.gleam           # structured Value type
    lexer.gleam / parser.gleam
    eval.gleam            # pipeline evaluator
    builtins.gleam        # Nu-inspired commands
    pager.gleam           # color-aware builtin less
    display.gleam         # table pretty-printer
    color.gleam           # Nushell-style ANSI colors
    highlight.gleam       # live input syntax highlighting
    env.gleam / sys.gleam

Input and output are colorized on a TTY (Nu-like shapes on the command line; headers bold green, numbers purple, bools cyan, dirs blue, errors red, …). External tools (jj, git, fastfetch, …) keep their own colors: final-stage commands inherit the real TTY; captured pipeline stages (e.g. jj log | less, git log | less) run under a throwaway PTY when the shell wants color so tools that only colorize on a terminal still emit ANSI — without per-tool env hacks. Nested pagers are forced to cat so the producer cannot hang in its own less. If script is unavailable, capture falls back to pipes plus FORCE_COLOR / CLICOLOR_FORCE and a git GIT_CONFIG_* overlay. Pre-colored text is not re-painted by the shell. While the raw line editor is active, the TTY is switched to cooked mode for those children so LF-only output does not staircase. The builtin less keeps ANSI (like less -R); external pagers still get LESS=FRX when unset so they pass colors through. Disable with NO_COLOR=1; force with FORCE_COLOR=1.

Status#

Early but usable: core pipeline model, tables, filters, JSON, and external commands work. Not a full Nushell clone (no closures/plugins yet). Contributions and experiments welcome.

License#

Apache-2.0 (same as the Gleam project template unless you change it).