# kaish (会sh)
**A predictable shell for AI agents** — Bourne-like syntax without the gotchas.
The 会 (kai) means "gathering" in Japanese. Part of [Kaijutsu](https://github.com/tobert/kaijutsu) (会術) — the art of gathering.
## Install
```bash
cargo install kaish
```
This is preferred for now while kaish is still experimental. Containers and binaries
are in future plans when things stabilize a bit more and I have time (or PRs!).
## Why kaish?
Traditional shells have evolved syntax with many sharp edges. kaish implements the
commonly-used parts of sh while eliminating entire classes of bugs at the language level:
- **No implicit word splitting** — `$VAR` is always one value, never split on spaces
- **No glob expansion** — tools handle their own patterns, or use `glob` builtin
- **Structured iteration** — `for i in $(seq 1 5)` works via structured data, not word splitting
- **Explicit splitting** — use `split "$VAR"` when you actually need word splitting
- **No backticks** — only `$(cmd)` substitution
- **Strict booleans** — `TRUE` and `yes` are errors, not truthy
- **Pre-validation** — catch errors before execution, not at runtime
Skills transfer from bash. Footguns don't.
## Quick Tour
```bash
#!/usr/bin/env kaish
# Familiar bash-style syntax
GREETING="Hello"
echo "$GREETING, world!"
# Control flow
if [[ -f config.json ]]; then
echo "Config found"
fi
# For loops - no implicit word splitting!
for item in one two three; do # literal items
echo "Processing: $item"
done
for i in $(seq 1 3); do # structured data iteration
echo "Count: $i"
done
for file in $(glob "*.txt"); do # structured data iteration
echo "Found: $file"
done
# Pipes and redirects
# Expand glob patterns
glob "**/*.rs" --exclude="*_test.rs"
# Parallel execution with scatter/gather
## Language Features
| **Bourne-compatible** | Variables, pipes, control flow, functions — familiar syntax |
| **66 builtins** | grep, jq, git, find, sed, awk, diff, patch, and more |
| **Structured data** | Commands return typed arrays — `for i in $(seq 1 5)` iterates 5 values, not word-split text |
| **Strict validation** | Errors caught before execution with clear messages |
| **Virtual filesystem** | Unified access: `/mnt/local` (home), `/scratch` (memory), `/v/jobs` (observability) |
| **Scatter/gather** | Built-in parallelism with 散/集 |
See [Language Reference](docs/LANGUAGE.md) for complete syntax. Use `help builtins` or `help <tool>` for per-tool docs.
---
## Builtins
kaish ships 66 builtins that run in-process — no subprocesses, no PATH lookups, no platform
variance. They exist because agents need tools they can verify: a `grep` that behaves identically
everywhere, a `jq` that always uses the same filter syntax, an `awk` that never surprises.
**Design principles:**
- **Verifiable** — each builtin has a schema (params, types, examples) exposed via `help <tool>`.
Agents can introspect before calling.
- **Convention-following** — flags and behavior match the patterns deeply embedded in training data
and decades of existing scripts. `grep -rn`, `sed 's/old/new/g'`, `awk '{print $1}'` all work
as expected.
- **80/20** — implement the features used 80% of the time, deliberately omit the 20% that add
complexity without proportional value. Missing features compose via pipes.
- **ERE everywhere** — all regex uses Extended Regular Expressions. No BRE/ERE confusion.
| **Text** | awk, cut, grep, head, sed, sort, split, tail, tr, uniq, wc |
| **Files** | basename, cat, cd, chmod, cp, dirname, find, glob, ln, ls, mkdir, mktemp, mv, pwd, read, readlink, realpath, rm, stat, tee, touch, tree, write |
| **JSON** | jq |
| **Git** | git (init, clone, status, add, commit, log, diff, branch, checkout, worktree) |
| **System** | date, echo, env, exec, export, help, hostname, jobs, kill, printf, ps, seq, set, sleep, spawn, test/\[\[, tokens, uname, unset, validate, vars, wait, which |
| **Parallel** | scatter, gather |
| **Meta** | assert, diff, false, mounts, patch, tools, true |
---
## Components
kaish is built as a set of crates that can be used independently:
### kaish-kernel
The core execution engine. Lexer, parser, interpreter, builtins, VFS.
```rust
use kaish_kernel::{Kernel, KernelConfig};
let kernel = Kernel::new(KernelConfig::default())?;
```
The kernel is embeddable — no external dependencies, no subprocess spawning for builtins.
### kaish-repl
Interactive shell with readline support, history, and tab completion.
```bash
$ kaish
kaish> for f in $(glob "*.rs"); do wc -l "$f"; done
142 main.rs
87 lib.rs
kaish>
```
### kaish-mcp
MCP server exposing kaish as tools for AI agents.
#### Installation
Add to your MCP client configuration:
```json
{
"mcpServers": {
"kaish": {
"command": "kaish-mcp"
}
}
}
```
#### Tools
**`execute`** — Run kaish scripts in a fresh, isolated environment.
```
Supports: pipes, redirects, here-docs, if/for/while, functions, builtins,
${VAR:-default}, $((arithmetic)), scatter/gather parallelism.
NOT supported: process substitution <(), backticks, eval, aliases.
Paths: /mnt/local = $HOME, /scratch/ = ephemeral memory.
```
**`help`** — Discover syntax, builtins, VFS, and capabilities.
```
Topics: overview, syntax, builtins, vfs, scatter, limits
Tool help: help grep, help jq, help git
```
#### Why an MCP shell?
AI agents need to compose operations — filter outputs, transform data, iterate over results.
Raw MCP tools are individual operations; kaish lets agents combine them:
```bash
# Filter and transform in one script
# Iterate over results
for f in $(glob "*.json"); do
jq ".name" "$f"
done
# Parallel processing
The kernel runs builtins in-process (no fork/exec), making it fast and predictable.
#### MCP Client Mode
kaish can also consume external MCP tools, appearing as namespaced commands:
```bash
# External MCP tools look like CLI commands
exa:web_search --query "rust parser combinators"
# Pipe MCP results through kaish builtins
github:list_issues --repo="foo/bar" | jq '.[] | .title'
```
---
## Building from Source
```bash
git clone https://github.com/tobert/kaish
cd kaish
cargo build --release
```
## Contributing
Agent-generated PRs are welcome! 🤖 This project is built with AI agents and we
love seeing what other agents come up with. That said, please have your agent (or
another model) review the PR before submitting — a quick sanity check goes a long
way. Same goes for issues: agent-filed is fine, just make sure it makes sense.
If you're working with AI coding agents, you might also be interested in:
- [**gpal**](https://github.com/tobert/gpal) — Gemini as an MCP server (pairs well with Claude Code)
- [**cpal**](https://github.com/tobert/cpal) — Claude as an MCP server (pairs well with Gemini CLI)
## License
MIT