Edit the downstream side of a shell pipeline and see its output update live, without re-running the upstream side.

zsh-halfpipe lets you iterate on filters, regexes, and other pipeline stages in place by pressing Ctrl-G.

git log --oneline | grep -E "fix"

Hit Ctrl-G. Now refine the regex — change it to "fix|feat", then "^[a-f0-9]+ (fix|feat):" — and see what matches instantly. The left side runs once; you iterate on the right without re-running git log.

Great for getting a regular expression right without executing the full pipeline on every attempt.

• The upstream command is cached on activation and shown in cyan.
• Press Ctrl-X Ctrl-G to re-run the upstream and refresh the cache.
• Press Ctrl-G again to exit. Press Enter to run the final command normally.
• Preview mode only live-executes explicitly allowlisted, stream-oriented commands. By default that list is awk, sed, grep, head, tail, tr, cut, sort, uniq, wc, cat, nl, column, and jq.

• Preview commands run in a zsh -fc subprocess hydrated with your current aliases and functions.
• Ctrl-G is borrowed while a pipeline is on the command line and restored when you exit.
• Ctrl-X Ctrl-G is bound while preview mode is active and released on exit.
• Output is cached when you first activate preview. Use Ctrl-X Ctrl-G to refresh it.
• Commands outside that allowlist are not executed in preview mode, even without globs. This avoids live-running perl, ad-hoc scripts, or destructive commands like rm.
• If you want to allow additional preview commands, set HALFPIPE_PREVIEW_COMMAND_ALLOWLIST before sourcing the plugin.

typeset -ga HALFPIPE_PREVIEW_COMMAND_ALLOWLIST=(awk sed grep head tail tr cut sort uniq wc cat nl column jq)
source ~/.local/share/zsh-halfpipe/halfpipe.zsh

This works whether you're using plain Zsh, Oh My Zsh, or any other setup.

mkdir -p ~/.local/share
git clone https://github.com/raimo/zsh-halfpipe.git ~/.local/share/zsh-halfpipe

Then add this line to your ~/.zshrc:

source ~/.local/share/zsh-halfpipe/halfpipe.zsh

git clone https://github.com/raimo/zsh-halfpipe.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-halfpipe

Then add zsh-halfpipe to your plugins array in ~/.zshrc:

plugins=(git zsh-halfpipe …)

zinit light raimo/zsh-halfpipe

antigen bundle raimo/zsh-halfpipe

The repo keeps the implementation in halfpipe.zsh and exposes a root-level zsh-halfpipe.plugin.zsh entrypoint for Oh My Zsh and other plugin managers that auto-detect *.plugin.zsh files.

Just remove the source line (or the plugin name from the plugins= array) and delete the cloned directory.

Syntax-check the script with:

zsh -n halfpipe.zsh

Run the plugin test suite with:

zsh tests/run.zsh

Mutation-check the test harness with:

zsh tests/test-the-test.zsh

The repo intentionally keeps the implementation in a single file so it can be sourced directly by shell plugin managers.

This software is provided as-is, without warranty of any kind, and you use it at your own risk. By using it, you accept full responsibility for reviewing what it does in your environment; the author disclaims liability for any loss, damage, or disruption resulting from its use. See LICENSE for the full license terms.

Core logic for this tool was created by a human and has been used daily in real workflows. AI was used to improve test coverage, help with documentation, and fix corner cases revealed by the test harness; it was not the origin of the core interaction design or primary implementation logic.