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
# 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.