powershell-windows

A guide to writing and debugging PowerShell scripts on Windows, with rules for operators, text output, null values, JSON depth, and errors.

In plain words
What is it for?
Use it when authoring or troubleshooting Windows PowerShell scripts that must handle conditions, missing values, JSON, and failures reliably.
Why use it?
It explains common PowerShell mistakes that can cause parser errors or silently incorrect results, especially under strict checking.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/phuonghx/aim-cli/powershell-windows
Any agent
npx skills add phuonghx/aim-cli --skill powershell-windows
Clone the repo
git clone --depth 1 https://github.com/phuonghx/aim-cli

Made for: Claude Code, Codex.

Per session 83 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,145 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00083 $0.01145
Opus 5 $0.00042 $0.00573
Sonnet 5 $0.00017 $0.00229
Haiku 4.5 $0.00008 $0.00114

Measured yesterday against content hash d7e7ad9200e2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

powershell-windows scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

aim/templates/aim-agents/skills/powershell-windows/SKILL.md · 139 lines

How it starts

The opening of the file, as written. The whole thing — 139 lines — stays where its author put it; the contents beside it link to each section on GitHub.

PowerShell on Windows

PowerShell has a handful of sharp edges that bite predictably. The rules below are not stylistic preferences -- ignoring them produces parser errors or silent wrong behavior.

Group cmdlet calls inside conditions

When a cmdlet result feeds a logical operator, wrap the call in parentheses. The parser otherwise treats -or/-and as a parameter to the cmdlet.

# Breaks: -or is read as an argument to Test-Path
if (Test-Path $a -or Test-Path $b) { ... }

# Works: each call is its own grouped expression
if ((Test-Path $a) -or (Test-Path $b)) { ... }

# Same rule with a comparison on one side
if ((Get-Item $p) -and ($count -eq 5)) { ... }

Stick to ASCII in script output

Non-ASCII glyphs (emoji, check marks, box drawing) cause "Unexpected token" errors on many Windows consoles and code pages. Use bracketed ASCII tags instead.

Meaning Avoid Use
Success check / tick marks [OK] [+]
Failure cross / red circle [X] [!]
Warning warning sign [WARN] [*]
Info info symbol [INFO] [i]
In progress hourglass [...]

Guard against null before dereferencing

Touching a property or method on $null throws -- and under Set-StrictMode even reading an unset variable does. Check first.

# Risky
if ($items.Count -gt 0) { ... }
$len = $name.Length

# Safe
if ($items -and $items.Count -gt 0) { ... }
if ($name) { $len = $name.Length }

Pull deep expressions out of strings

Interpolating a multi-hop property chain inside a string is fragile. Assign it to a variable, then interpolate the variable.

# Fragile
Write-Output "City: $($order.customer.address.city)"

# Clear
$city = $order.customer.address.city
Write-Output "City: $city"

Choose the right error preference

$ErrorActionPreference sets how non-terminating errors behave:

Value Fits
Stop development -- fail loudly and early
Continue production scripts that should push through
SilentlyContinue spots where an error is expected and fine

Read the full file on GitHub · 139 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 139 lines · 83 tokens per session scan A d7e7ad9200e2

Subscribe to this mod's changes

powershell-windows is a skill published in the GitHub repository phuonghx/aim-cli (1 stars, last pushed 2mo ago), licensed MIT. It adds 83 tokens to every session and 1,145 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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