PowerShell

Avoid common PowerShell mistakes — output behavior, array traps, and comparison operator gotchas.

Security Scan

This is a documentation-only PowerShell tips skill that only requires the pwsh binary and its contents are coherent with the stated purpose.

Purpose & Capability

Name and description (PowerShell gotchas & tips) align with the declared requirement of the pwsh binary. No unrelated binaries, credentials, or config paths are requested.

Instruction Scope

SKILL.md is purely advisory: it lists tips, examples, and best practices. It does not instruct the agent to read arbitrary files, access credentials, call external endpoints, or perform data exfiltration.

Install Mechanism

No install spec and no code files — instruction-only skill. Nothing will be downloaded or written to disk by the skill itself.

Credentials

The skill requests no environment variables or credentials. It mentions using $env:VAR in a descriptive context only, which is appropriate for documentation.

Persistence & Privilege

always:false (default) and the skill does not request persistent system presence or attempt to modify other skills or system settings. Model invocation is allowed by default (normal for skills) but the skill itself is read-only documentation.

Assessment

This skill is just documentation (no code) and only requires the pwsh binary to be present, so the surface area is small. However, the registry entry has no homepage and an unknown source — if you rely on vendor provenance, verify the origin or prefer a documented source. Also note: while the skill itself won't run code, if you allow an autonomous agent to execute PowerShell on your machine, PowerShell can perform powerful system actions; only enable execution in environments you trust.

Output Behavior

• Everything not captured goes to output — even without return or Write-Output
• return doesn't stop output — previous uncaptured expressions still output
• Write-Host bypasses pipeline — use for display only, not data
• Assign to $null to suppress — $null = SomeFunction
• [void] cast also suppresses — [void](SomeFunction)

Array Gotchas

• Single item result is scalar, not array — @(Get-Item .) forces array
• Empty result is $null, not empty array — check with if ($result) carefully
• Array unrolling in pipeline — @(1,2,3) | ForEach sends items one by one
• += on array creates new array — slow in loops, use [System.Collections.ArrayList]
• , is array operator — ,$item wraps single item in array

Comparison Operators

• -eq, -ne, -gt, -lt — not ==, !=, >, <
• -like with wildcards, -match with regex — both return bool
• -contains for array membership — $arr -contains $item, not $item -in $arr (though -in works too)
• Case-insensitive by default — -ceq, -cmatch for case-sensitive
• $null on left side — $null -eq $var prevents array comparison issues

String Handling

• Double quotes interpolate — "Hello $name" expands variable
• Single quotes literal — '$name' stays as literal text
• Subexpression for complex — "Count: $($arr.Count)" for properties/methods
• Here-strings for multiline — @" ... "@ or @' ... '@
• Backtick escapes — `n for newline, `t for tab

Pipeline

• $_ or $PSItem is current object — same thing, $_ more common
• ForEach-Object for pipeline — foreach statement doesn't take pipeline
• -PipelineVariable saves intermediate — Get-Service -PV svc | Where ...
• Pipeline processes one at a time — unless function doesn't support streaming

Error Handling

• $ErrorActionPreference sets default — Stop, Continue, SilentlyContinue
• -ErrorAction Stop per command — makes non-terminating errors terminating
• try/catch only catches terminating — set ErrorAction Stop first
• $? is last command success — $LASTEXITCODE for native commands

Common Mistakes

• No space before { in if — if($x){ works but if ($x) { preferred
• = is assignment in conditions — use -eq for comparison
• Function return array unrolls — return ,@($arr) to keep array
• Get-Content returns lines array — -Raw for single string
• Select-Object creates new object — properties are copies, not references

Cross-Platform

• pwsh is PowerShell 7+ — powershell is Windows PowerShell 5.1
• Paths use / or \ — Join-Path for portable
• Environment vars: $env:VAR — works on all platforms
• Aliases differ across platforms — ls, cat may not exist, use full cmdlet names