CommandFixer

A lightweight Go binary that catches your common typing mistakes in PowerShell before commands execute.

Type git sattus, press Enter and CommandFixer offers git status; the corrected line runs once you accept it.

Works in both PowerShell 7 (pwsh) and Windows PowerShell 5 (powershell.exe).

Commercial licences available. CommandFixer is free and open source under GPL-3.0. If those terms do not suit what you are building, such as a closed-source product, a commercial licence can be bought from me separately. It covers my own code; the Go standard library it is built with keeps its own licence. See commercial licensing.

Who it is for and who it is not for

It is for someone who lives in PowerShell on Windows and mistypes the same handful of commands often enough to want them corrected in place. Suggestions arrive through a PSReadLine hook and nothing is rewritten behind your back: you confirm before the corrected command runs.

It is not a shell, not a replacement for tab completion and not a command generator. It matches against a database of common CLI tools using a similarity threshold, so it corrects spelling rather than intent: it will turn a misspelt command into the one you meant to type, never a wrong command into the right one. It only looks at lines of two words or more, so a lone mistyped word such as ipconfg is left as typed. It works by hooking PowerShell profiles on Windows and has no meaning outside that environment.

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What it does

• Corrects a mistyped subcommand of a known tool (git sattus to git status, npm isntall to npm install), keeping every argument after it.
• Corrects a mistyped tool or Windows command name (dokcer ps to docker ps, ipconfg /all to ipconfig /all) and the habitual gti to git.
• Never renames a first word that already runs as a command on your PATH, so a program the database has never heard of is left alone.
• Asks before anything changes: Y or Enter accepts, any other key keeps the line.
• Holds input that would open PowerShell's >> continuation prompt (a trailing backtick is stripped; an unclosed quote or a dangling pipe beeps and stays on the line).
• Logs each accepted correction to a local file and counts them on request.

Stack

Part	What
Language	Go 1.21 or later, standard library only, no cgo
Prompt hook	PSReadLine, in PowerShell 7 and Windows PowerShell 5
Install and build	PowerShell scripts: build.ps1, install.ps1, uninstall.ps1
Storage	A JSON settings file and a JSONL log in your home directory

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Quick Start

1. Build

git clone https://github.com/oernster/commandfixer
cd commandfixer
.\build.ps1 -Test        # run tests then build

Or with go directly:

go build -o commandfixer.exe .

2. Install

.\install.ps1

The installer:

• Copies commandfixer.exe to %LOCALAPPDATA%\CommandFixer\
• Adds that directory to your user PATH
• Copies config.example.json to %USERPROFILE%\.typo-fixer\config.json when you have no config there yet
• Hooks into your PowerShell profile for both PS7 and PS5

Everything is per user, so no administrator rights are needed. Then restart PowerShell (both pwsh and powershell.exe will have the hook).

3. Uninstall

.\uninstall.ps1

The uninstaller:

• Removes the hook from both PS7 (Documents\PowerShell\profile.ps1) and PS5 (Documents\WindowsPowerShell\profile.ps1)
• Deletes the %LOCALAPPDATA%\CommandFixer\ folder, binary included
• Removes that directory from your user PATH
• Keeps your config and log at %USERPROFILE%\.typo-fixer\ (data is yours)

To also delete config and log:

.\uninstall.ps1 -RemoveConfig

Then restart PowerShell to complete removal.

You can also uninstall via the binary directly (if it is on your PATH):

commandfixer uninstall   # removes profile hooks only; does not touch binary or PATH

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Reinstall / Upgrade

To upgrade to a new build (or reinstall after code changes), rebuild and re-run the installer. install.ps1 is idempotent: it overwrites the existing binary with -Force and leaves your PATH entry and your config/log untouched. It adds the PowerShell profile hook to any profile that lacks it; a profile that already has the hook is left exactly as it is.

.\build.ps1 -Test        # rebuild commandfixer.exe (runs tests first)
.\install.ps1            # overwrite the installed binary

No restart is needed. The hook runs the installed binary by its full path on every Enter, so open shells use the new build straight away.

If a release changes the hook itself, re-running the installer does not update it. Remove the old hook first, then install and restart PowerShell, since a profile registers the hook once at startup:

& "$env:LOCALAPPDATA\CommandFixer\commandfixer.exe" uninstall
.\install.ps1

For a clean reinstall that also resets your config and log, uninstall with -RemoveConfig first, then install:

.\uninstall.ps1 -RemoveConfig
.\build.ps1
.\install.ps1

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4. Configure

There is nothing you have to configure. Corrections come from a database built into the binary, so it is useful the moment it is installed.

If you want to tune it, edit %USERPROFILE%\.typo-fixer\config.json:

{
  "settings": {
    "log_file": "",
    "max_log_lines": 10000,
    "similarity_threshold": 0.6
  }
}

similarity_threshold is how close a typo must be to a known command before it is offered, in the range (0.0, 1.0]; a value outside it falls back to 0.6. Lower catches more typos and starts offering corrections you did not want. log_file empty means the default location below. max_log_lines is read but nothing acts on it: the log is never trimmed.

5. Use It

Type a mistyped command and press Enter:

PS> git sattus
CommandFixer: did you mean: git status [Y/n]
On branch main ...

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How It Works

CommandFixer hooks into PSReadLine (built into both PowerShell 7 and Windows PowerShell 5) and intercepts the Enter key. When you press Enter:

1. PSReadLine captures the current buffer.
2. It calls commandfixer suggest <your-command>.
3. CommandFixer fuzzy-matches it against a built-in database of CLI tools, their subcommands and the standard Windows commands and prints a suggestion when one is close enough. Nothing is printed when it has nothing to offer.
4. If there is a suggestion, PowerShell shows it and waits for you to confirm.
5. The corrected command executes only if you accept it.

No system-wide keyboard hooks. No persistent service required. The binary runs once each time you press Enter on a command, then exits. Nothing it does reaches the network.

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CLI Commands

commandfixer suggest <cmd>       Fuzzy-match and print correction (used by hook)
commandfixer correct <cmd>       Like suggest but also logs the correction
commandfixer log <from> <to>     Record a correction you accepted (used by hook)
commandfixer install [profile]   Add PSReadLine hook to your profile(s)
commandfixer uninstall [profile] Remove the hook from your profile(s)
commandfixer stats               Show how many corrections have been logged
commandfixer version             Print version
commandfixer help                Show help

Without a [profile] argument, install and uninstall target both PS7 and PS5 profiles simultaneously.

Manual correction check

commandfixer correct "git sattus"
# Prints: git status (and records the correction in the log)

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Files

Path	Purpose
%USERPROFILE%\.typo-fixer\config.json	Settings: log location and match sensitivity
%USERPROFILE%\.typo-fixer\corrections.log	JSONL corrections log
%LOCALAPPDATA%\CommandFixer\commandfixer.exe	Installed binary
Documents\PowerShell\profile.ps1	PS7 profile (hook appended here)
Documents\WindowsPowerShell\profile.ps1	PS5 profile (hook appended here)

Documents is the folder Windows reports as your Documents folder, the same one PowerShell reads its profile from, so a Documents folder moved by OneDrive folder backup is followed rather than ignored.

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Testing

.\build.ps1 -Coverage    # the whole suite, failing below the coverage floor
.\build.ps1 -Lint        # gofmt, go vet and staticcheck

TESTING.md covers the floor, what each suite proves and how to run part of it.

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Further Reading

• DEVELOPMENT.md: build steps, local dev workflow, debugging
• ARCHITECTURE.md: system design, module breakdown, data flow
• TESTING.md: testing strategy, coverage requirements, how to run tests
• TECH_DEBT.md: what is still open, what is deliberately left and what only looks like debt
• DECISIONS-TRADEOFFS.md: the decisions CommandFixer rests on, with what each one gains and what it costs

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Supporting the project

CommandFixer is free and stays free. There is no paid tier, no licence key and no feature held back behind a donation. If it has saved you time or simply been useful, a donation supports its maintenance and continued development.

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Licence

CommandFixer is released under the GNU General Public License v3.0; see LICENSE.

A commercial licence is available for uses the GPL does not suit: see commercial licensing.