Show HN: Pu.sh – a full coding-agent harness in 400 lines of shell
I originally was just messing with pi-autoresearch. Gave it a sample task to build the most portable coding agent. First cut was 6 KB of shell. Great for one-shots, unusable interactively. I was shocked it actually worked. Started building up -- adding features — but with a self-imposed rule: no new dependencies, and sub 500 LOC. This thing had to be truly portable. Just sh, curl, awk. System primitives only. Which means I did some genuinely disgusting things in awk, including JSON parsing and the OpenAI Responses tool loop with reasoning items carried across turns. It's now ~400 lines. In the box: Anthropic + OpenAI, 7 tools (bash, read, write, edit, grep, find, ls), REPL, auto-compaction, checkpoint/resume, pipe mode, 90 no-API tests. Not in the box: TUI, streaming, images, OAuth, Windows, dignity. Two honest things: 1. I stole/modified the system prompt and the architecture. Pi/Claude/Codex wrote the awk. I cannot read most of this code. This wasn't possible for me a year ago. 2. Heavily inspired by Pi (pi.dev) — same 7-tool surface, same exact-text edit model. Credit where it's due. Pi is awesome -- you should probably use them. The agent loop itself is tiny. Almost everything else in a "real" agent CLI is DX and hardening. You can probably build your own harness exactly how you like it. Mario Zechner's AI Engineer talk on taking back control of your tools nudged me here. The name is because it's a .sh file. The other thing it sounds like is, regrettably, also accurate.
Discussion Highlights (12 comments)
petcat
your 500 LOC requirement has made this thing completely and unnecessarily inscrutable and unreadable. Pass.
hkt
I love it. I think I'm going to have fun with this and possibly learn a bit, too. I'm pondering a container based dev environment at the moment and might throw it in with busybox and see how far I get :)
ricardobeat
Really like the looks of it, but minifying the code to achieve the “400 lines” marketing gimmick is a huge turn-off. It’s also a security nightmare, and ensures it remains 100% vibe coded. Would rather have a readable source with an honest line count.
flog
I'd love to learn how to build something like this, but unfortunately the code is unreadable. If author could write a heavily commented version that would be amazing.
Imustaskforhelp
Interested in something like this if the code can be more readable, it would be interesting to see it in languages like lua etc. too in future.
kkovacs
I love this. This is the grown-up brother of my one-liner bash+python at https://github.com/kkovacs/kkrc/blob/ecff1f65d5ccfa24d5f6695... :)
tecoholic
Kudos. I set on this exact journey a couple of days back and Pi is what I started reading for inspiration as well. I really can't stand the text boxes and the animations of the mainstream harnesses.
cachius
Does it work in just-bash? https://github.com/vercel-labs/just-bash/blob/main/packages/...
mjuarez
Could you post the initial 6KB version? I'd love to have a version that I can actually read and understand. I don't care if it's 2K LOC.
0gs
why the LOC limit? just because?
zackham
if you are looking for a customizable agent harness that provides everything except a tui (cli, acp, embeddable python package) i built and use this for a handful of projects where i needed a vendor-agnostic replacement for claude agent sdk: https://github.com/zackham/aloop
Amber-chen
I like the small-surface-area approach. The question I’d use to evaluate this is how well the harness records/replays tool calls and failure modes, since that is where debugging agent behavior usually gets messy.