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.

gleshell:gleshell> ls | where type == file | select name size | first 5
╭──────┬──────╮
│ name │ size │
├──────┼──────┤
│ …    │ …    │
╰──────┴──────╯

Quick start#

Requires Gleam and Erlang (or use Nix):

# with Nix flake (dev shell: gleam, erlang, rebar3)
# --no-pure-eval lets devenv use the real project dir (not /nix/store)
nix develop --no-pure-eval
gleam run                 # interactive REPL
gleam run -- -c 'ls | first 3'
gleam test

# or one-shot from the repo root
nix run . -- -c 'ls | first 3'

# or if gleam is already on PATH
gleam run

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, …).

Key	Action
↑ / ↓	History
Tab	Filename completion (common prefix; list matches if ambiguous)
Ctrl+R	Reverse-i-search through history
Ctrl+A / Ctrl+E	Beginning / end of line
Ctrl+W	Delete previous word
Ctrl+U / Ctrl+K	Kill to start / end of line
Ctrl+L	Clear screen
Ctrl+C	Cancel current line (does not exit the shell)
Ctrl+D	EOF (empty line) or delete under cursor

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

# 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

Language sketch#

Feature	Syntax
Pipeline	`cmd \| cmd \| cmd`
Strings	`"hello"` or bare words `hello`
Numbers	`42`, `3.14`
Bools	`true` / `false`
Nothing	`null` / `nothing`
Lists	`[1 2 3]`
Records	`{name: alice, age: 30}`
Variables	`let x = …` then `$x` (pipeline input is `$in`)
Env	`$env`, `$env.HOME`, `$env.FOO = value`
Flags	`--flag` / `--flag value`
Force external	`^command args…`
Comments	`# …`

Built-ins#

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

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

Data: echo, range, lines, to json, from json, type, describe, env, sys, which, help, exit

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
    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, …). 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).

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