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@plotdb/esh

esh — embeddable shell runtime for JavaScript.

A shell syntax interpreter with a virtual file system. Runs in the browser ( with optional OPFS persistence ), in Node, and in workers.

Supported syntax: pipes, redirects ( > >> < 2>, heredoc ), variable expansion and quoting, glob, command substitution $(...), arithmetic $(( )), if / for / while / case, functions, local, $@, custom IFS, xargs, and more. Commands are currently provided by ShellJS; see the project plan for the evolution roadmap.

Usage

Browser ( ESM )

<script type="module">
  import { createShell } from '@plotdb/esh';   // with a bundler
  // or directly: import { createShell } from './dist/esh.js';
  const sh = await createShell();
  const r = await sh.run('ls | grep foo');     // { stdout, stderr, code }
</script>

With OPFS persistence:

const sh = await createShell({ mounts: { '/home': { backend: 'opfs' } } });
// scope storage per page: { backend: 'opfs', path: 'my-app' } mounts a
// subdirectory of origin storage; { backend: 'indexeddb', storeName: 'x' }
// uses a separate store — same-origin workspaces stay isolated.
// note: changing `path` later only moves the mount point — data written
// under the old path stays where it was on disk, and may resurface at
// unexpected virtual locations; migrate or clean up old directories

Browser ( non-ESM, window.esh )

<script src="dist/esh.iife.js"></script>
<script>
  esh.createShell().then(function(sh) { sh.run('echo hi'); });
</script>

Node

import { createShell } from '@plotdb/esh';   // real fs, no shims needed
const sh = await createShell();
// sandbox: createShell({ fs: a memfs instance }) — note that fs and shell
// must share the same fs implementation; see src/base.js

Node with virtual fs ( @plotdb/esh/node-zenfs )

Same behavior as the browser bundle — mounts, root ( chroot ) and the device backend all work; the browser's opfs maps to passthrough ( a real-disk subdirectory mounted into the virtual fs ):

import { createShell } from '@plotdb/esh/node-zenfs';
const sh = await createShell({ mounts: {
  '/home': { backend: 'passthrough', path: '/srv/ws/u123' }
}, root: '/home/workspace' });

All backends here are synchronous. Real symlinks inside the passthrough directory that resolve outside of it are rejected ( EACCES ) by default; pass followSymlinks: true on the mount to disable the guard. Requires node >= 20.16.

Terminal ( esh-term, shipped with the main package as separate files )

<link rel="stylesheet" href="dist/esh-term.css">
<script src="dist/esh-term.iife.js"></script>
<script>
  // deploy dist/esh-worker.js next to esh-term, or pass workerUrl
  eshTerm.createTerminal(document.getElementById('term'));
</script>

ESM: import { createTerminal } from '@plotdb/esh/term'. The shell runs in a Web Worker ( esh-worker.js, which contains the full engine ), with /home mounted on OPFS for persistence.

Cross-thread shell ( serveShell / connectShell )

Serve a shell from a worker and use it from the main thread ( or any postMessage-shaped transport ). Multiple clients can share one worker:

// worker
import { createShell, serveShell } from '@plotdb/esh';
const sh = await createShell({ mounts: { '/home': { backend: 'opfs' } } });
serveShell(sh, self);

// main thread
import { connectShell } from '@plotdb/esh';
const sh = await connectShell(worker);       // or a worker URL
await sh.run('ls');
await sh.io.writeFile('/home/web/data.csv', text);   // content bypasses the parser
await sh.io.readFile('/home/web/img.png', null);     // Uint8Array
await sh.io.readdir('/home', { withFileTypes: true }); // [{name, isDirectory}]
await sh.io.stat('/home/web/data.csv');   // {size, mtimeMs, isFile, isDirectory}

Local shells expose the same sh.io subset, so consumer code works with either. serveShell uses addEventListener and only handles its own message types ( exec / fs / hello ) — your own worker protocol can coexist.

Git ( optional command pack, @plotdb/esh/git )

Local-only git commands backed by isomorphic-git ( init / config / add / status / commit / log / branch / checkout ). Not included in the main bundle — opt in per shell:

import { createShell } from '@plotdb/esh';
import { installGit } from '@plotdb/esh/git';
const sh = installGit(await createShell());
await sh.run('git init && git config user.name me && git config user.email m@e');
await sh.run('echo hi > a.txt && git add . && git commit -m first');

Network commands ( clone / fetch / pull / push ) are not supported yet.

Scoped root ( chroot — browser bundle and node-zenfs )

const sh = await createShell({ root: '/home/ws/blocks/foo' });
await sh.run('ls');          // sees only foo/* — "/" is the root;
                             // cd .. / absolute paths / globs can't escape
sh.chroot('/home/ws/blocks/bar');   // host-side JS API; retarget the root

Multiple shells can share one fs with different roots ( restricted agent + unrestricted user terminal ), seeing each other's writes.

Device backend ( callback-backed files — browser bundle and node-zenfs )

const sh = await createShell({ mounts: {
  '/dev': { backend: 'device', files: {
    sheet: { read: () => currentSheetAsCSV(),      // live value, no caching
             write: (s) => applySheet(s) }         // omit write = read-only ( EROFS )
  } }
} });
await sh.run('grep total /dev/sheet | wc -l');     // shell tools work on live data

Advanced: bring your own dependencies ( base layer )

import { esh } from '@plotdb/esh/base';
const sh = esh({ fs, shell, parse, fg });    // bundler-agnostic

Development

  • npm run build — bundle with esbuild into dist/ ( esm + iife ), then copy to web/static/assets/esh/

  • npm run dev — vite dev server for regression test pages under web/vitedev/: m2.html ( command survival table, 81 cases ), m25.html ( syntax cases, 72 cases ), terminal.html ( xterm + worker + OPFS )

  • npm run web ( alias: npm start ) — fedev template server ( web/, consuming dist/ artifacts only ); the landing page links two demos: /terminal/ ( xterm + built-in worker, OPFS persistent, popup test suite ) and /custom/ ( consumer-authored worker: registerCommand with an async ask via a hostcall round-trip to a page dialog, plus the git pack, wired up with serveShell — try ask how many?, git init )

  • npm run console — interactive shell in the terminal ( node-zenfs sandbox; npm run build first ). Mount a real directory and jail it:

    npm run console -- --mount /home=./some/dir --root /home

Vite is only used by the test pages under web/vitedev/, which need source-level alias resolution; the shipped artifacts and the web/ demo do not depend on vite. The early PoC ( poc-shelljs/ ) has been removed; see git history for the full evolution.

License

MIT