@ag-bash/bash

A virtual bash environment with an in-memory filesystem, written in TypeScript and designed for AI agents.

Broad support for standard unix commands and bash syntax with optional curl, Python, JS/TS, and sqlite support.

Note: This is beta software. Use at your own risk and please provide feedback. See security model.

Installation

Globally (CLI & Shell)

Via Homebrew (macOS)

brew tap ag-bash/homebrew-tap
brew install ag-bash

Via NPM

npm install -g @ag-bash/bash

As a Library

npm install @ag-bash/bash

import { Bash } from "@ag-bash/bash";

const bash = new Bash();
await bash.exec('echo "Hello" > greeting.txt');
const result = await bash.exec("cat greeting.txt");
console.log(result.stdout); // "Hello\n"
console.log(result.exitCode); // 0

Each exec() call gets its own isolated shell state — environment variables, functions, and working directory reset between calls. The filesystem is shared across calls, so files written in one exec() are visible in the next.

Custom Commands

Extend @ag-bash/bash with your own TypeScript commands using defineCommand:

import { Bash, defineCommand } from "@ag-bash/bash";

const hello = defineCommand("hello", async (args, ctx) => {
  const name = args[0] || "world";
  return { stdout: `Hello, ${name}!\n`, stderr: "", exitCode: 0 };
});

const upper = defineCommand("upper", async (args, ctx) => {
  return { stdout: ctx.stdin.toUpperCase(), stderr: "", exitCode: 0 };
});

const bash = new Bash({ customCommands: [hello, upper] });

await bash.exec("hello Alice"); // "Hello, Alice!\n"
await bash.exec("echo 'test' | upper"); // "TEST\n"

Custom commands receive a CommandContext with fs, cwd, env, stdin, and exec (for subcommands), and work with pipes, redirections, and all shell features.

File Operations

cat, cp, file, ln, ls, mkdir, mv, readlink, rm, rmdir, split, stat, touch, tree

Text Processing

awk, base64, column, comm, cut, diff, expand, fold, grep (+ egrep, fgrep), head, join, md5sum, nl, od, paste, printf, rev, rg, sed, sha1sum, sha256sum, sort, strings, tac, tail, tr, unexpand, uniq, wc, xargs

Data Processing

jq (JSON), sqlite3 (SQLite), xan (CSV), yq (YAML/XML/TOML/CSV)

Optional Runtimes

js-exec (JavaScript/TypeScript via QuickJS; requires javascript: true), python3/python (Python via CPython; requires python: true)

Compression & Archives

gzip (+ gunzip, zcat), tar

Navigation & Environment

basename, cd, dirname, du, echo, env, export, find, hostname, printenv, pwd, tee

Shell Utilities

alias, bash, chmod, clear, date, expr, false, hello, help, history, seq, sh, sleep, time, timeout, true, unalias, which, whoami

Agentic Operations (v2.0.0+)

Specialized commands designed for AI agents to interact with the environment effectively:

• ag-edit: Robust, line-based file editing (insert/replace/delete).
• ag-diff: High-fidelity, semantic diff for code changes.
• ag-snapshot: Capture and restore core shell state (env, functions, CWD, and FS).
• ag-analyze: Structural analysis of Bash scripts with symbol table extraction.
• ag-hover: Retrieve metadata and documentation for a symbol at a specific location.
• ag-explain: Parse and explain the structure of complex shell commands.
• ag-find-symbol: Workspace-wide search for symbol definitions and references.
• ag-todo: Persistent local task management for agentic project tracking.

All commands support --help for usage information.

Shell Features

• Pipes: cmd1 | cmd2
• Redirections: >, >>, 2>, 2>&1, <
• Command chaining: &&, ||, ;
• Variables: $VAR, ${VAR}, ${VAR:-default}
• Positional parameters: $1, $2, $@, $#
• Glob patterns: *, ?, [...]
• If statements: if COND; then CMD; elif COND; then CMD; else CMD; fi
• Functions: function name { ... } or name() { ... }
• Local variables: local VAR=value
• Loops: for, while, until
• Symbolic links: ln -s target link
• Hard links: ln target link

Configuration

const env = new Bash({
  files: { "/data/file.txt": "content" }, // Initial files
  env: { MY_VAR: "value" }, // Initial environment
  cwd: "/app", // Starting directory (default: /home/user)
  executionLimits: { maxCallDepth: 50 }, // See "Execution Protection"
  python: true, // Enable python3/python commands
  javascript: true, // Enable js-exec command
  // Or with bootstrap: javascript: { bootstrap: "globalThis.X = 1;" }
});

// Per-exec overrides
await env.exec("echo $TEMP", { env: { TEMP: "value" }, cwd: "/tmp" });

// Pass stdin to the script
await env.exec("cat", { stdin: "hello from stdin\n" });

// Start with a clean environment
await env.exec("env", { replaceEnv: true, env: { ONLY: "this" } });

// Pass arguments without shell escaping (like spawnSync)
await env.exec("grep", { args: ["-r", "TODO", "src/"] });

// Cancel long-running scripts
const controller = new AbortController();
setTimeout(() => controller.abort(), 5000);
await env.exec("while true; do sleep 1; done", { signal: controller.signal });

// Preserve leading whitespace (e.g., for heredocs)
await env.exec("cat <<EOF\n  indented\nEOF", { rawScript: true });

exec() options:

| Option | Type | Description | |---|---|---| | env | Record<string, string> | Environment variables for this execution only | | cwd | string | Working directory for this execution only | | stdin | string | Standard input passed to the script | | args | string[] | Additional argv passed directly to the first command (bypasses shell parsing; does not change $1, $2, ...) | | replaceEnv | boolean | Start with empty env instead of merging (default: false) | | signal | AbortSignal | Cooperative cancellation; stops at next statement boundary | | rawScript | boolean | Skip leading-whitespace normalization (default: false) | | persistState | boolean | If true, commit env/cwd/function changes back to master instance |

Filesystem Options

Four filesystem implementations:

InMemoryFs (default) - Pure in-memory filesystem, no disk access:

import { Bash } from "@ag-bash/bash";

const env = new Bash({
  files: {
    "/data/config.json": '{"key": "value"}',
    // Lazy: called on first read, cached. Never called if written before read.
    "/data/large.csv": () => "col1,col2\na,b\n",
    "/data/remote.txt": async () => (await fetch("https://example.com")).text(),
  },
});

OverlayFs - Copy-on-write over a real directory. Reads come from disk, writes stay in memory:

import { Bash } from "@ag-bash/bash";
import { OverlayFs } from "@ag-bash/bash/fs/overlay-fs";

const overlay = new OverlayFs({ root: "/path/to/project" });
const env = new Bash({ fs: overlay, cwd: overlay.getMountPoint() });

await env.exec("cat package.json"); // reads from disk
await env.exec('echo "modified" > package.json'); // stays in memory

ReadWriteFs - Direct read-write access to a real directory. Use this if you want the agent to be able to write to your disk:

import { Bash } from "@ag-bash/bash";
import { ReadWriteFs } from "@ag-bash/bash/fs/read-write-fs";

const rwfs = new ReadWriteFs({ root: "/path/to/sandbox" });
const env = new Bash({ fs: rwfs });

await env.exec('echo "hello" > file.txt'); // writes to real filesystem

Keep ReadWriteFs pointed at a workspace directory, not at the installed @ag-bash/bash package or any other trusted runtime code. Guest-writable roots should stay separate from trusted code.

MountableFs - Mount multiple filesystems at different paths. Combines read-only and read-write filesystems into a unified namespace:

import { Bash, MountableFs, InMemoryFs } from "@ag-bash/bash";
import { OverlayFs } from "@ag-bash/bash/fs/overlay-fs";
import { ReadWriteFs } from "@ag-bash/bash/fs/read-write-fs";

const fs = new MountableFs({ base: new InMemoryFs() });

// Mount read-only knowledge base
fs.mount("/mnt/knowledge", new OverlayFs({ root: "/path/to/knowledge", readOnly: true }));

// Mount read-write workspace
fs.mount("/home/agent", new ReadWriteFs({ root: "/path/to/workspace" }));

const bash = new Bash({ fs, cwd: "/home/agent" });

await bash.exec("ls /mnt/knowledge"); // reads from knowledge base
await bash.exec("cp /mnt/knowledge/doc.txt ./"); // cross-mount copy
await bash.exec('echo "notes" > notes.txt'); // writes to workspace

Security Model

• The shell only has access to the provided filesystem.
• All execution happens without VM isolation. This does introduce additional risk. The code base was designed to be robust against prototype-pollution attacks and other break outs to the host JS engine and filesystem.
• There is no network access by default. When enabled, requests are checked against URL prefix allow-lists and HTTP-method allow-lists.
• Python and JavaScript execution are off by default as they represent additional security surface.

License

Apache-2.0