Agent skill

powershell-windows

PowerShell Windows patterns. Critical pitfalls, operator syntax, error handling.

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npx add-skill https://github.com/davila7/claude-code-templates/tree/main/cli-tool/components/skills/development/powershell-windows

SKILL.md

PowerShell Windows Patterns

Critical patterns and pitfalls for Windows PowerShell.


1. Operator Syntax Rules

CRITICAL: Parentheses Required

❌ Wrong ✅ Correct
if (Test-Path "a" -or Test-Path "b") if ((Test-Path "a") -or (Test-Path "b"))
if (Get-Item $x -and $y -eq 5) if ((Get-Item $x) -and ($y -eq 5))

Rule: Each cmdlet call MUST be in parentheses when using logical operators.


2. Unicode/Emoji Restriction

CRITICAL: No Unicode in Scripts

Purpose ❌ Don't Use ✅ Use
Success ✅ ✓ [OK] [+]
Error ❌ ✗ 🔴 [!] [X]
Warning ⚠️ 🟡 [*] [WARN]
Info ℹ️ 🔵 [i] [INFO]
Progress [...]

Rule: Use ASCII characters only in PowerShell scripts.


3. Null Check Patterns

Always Check Before Access

❌ Wrong ✅ Correct
$array.Count -gt 0 $array -and $array.Count -gt 0
$text.Length if ($text) { $text.Length }

4. String Interpolation

Complex Expressions

❌ Wrong ✅ Correct
"Value: $($obj.prop.sub)" Store in variable first

Pattern:

$value = $obj.prop.sub
Write-Output "Value: $value"

5. Error Handling

ErrorActionPreference

Value Use
Stop Development (fail fast)
Continue Production scripts
SilentlyContinue When errors expected

Try/Catch Pattern

  • Don't return inside try block
  • Use finally for cleanup
  • Return after try/catch

6. File Paths

Windows Path Rules

Pattern Use
Literal path C:\Users\User\file.txt
Variable path Join-Path $env:USERPROFILE "file.txt"
Relative Join-Path $ScriptDir "data"

Rule: Use Join-Path for cross-platform safety.


7. Array Operations

Correct Patterns

Operation Syntax
Empty array $array = @()
Add item $array += $item
ArrayList add `$list.Add($item)

8. JSON Operations

CRITICAL: Depth Parameter

❌ Wrong ✅ Correct
ConvertTo-Json ConvertTo-Json -Depth 10

Rule: Always specify -Depth for nested objects.

File Operations

Operation Pattern
Read `Get-Content "file.json" -Raw
Write `$data

9. Common Errors

Error Message Cause Fix
"parameter 'or'" Missing parentheses Wrap cmdlets in ()
"Unexpected token" Unicode character Use ASCII only
"Cannot find property" Null object Check null first
"Cannot convert" Type mismatch Use .ToString()

10. Script Template

powershell
# Strict mode
Set-StrictMode -Version Latest
$ErrorActionPreference = "Continue"

# Paths
$ScriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path

# Main
try {
    # Logic here
    Write-Output "[OK] Done"
    exit 0
}
catch {
    Write-Warning "Error: $_"
    exit 1
}

Remember: PowerShell has unique syntax rules. Parentheses, ASCII-only, and null checks are non-negotiable.

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