PowerShell Windows Patterns
Critical patterns and pitfalls for Windows PowerShell.
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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.
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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.
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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 } |
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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
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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.
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7. Array Operations
Correct Patterns
| Operation | Syntax | |
|---|---|---|
| Empty array | $array = @() | |
| Add item | $array += $item | |
| ArrayList add | `$list.Add($item) | Out-Null` |
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8. JSON Operations
CRITICAL: Depth Parameter
| ❌ Wrong | ✅ Correct |
|---|---|
ConvertTo-Json | ConvertTo-Json -Depth 10 |
Rule: Always specify -Depth for nested objects.
File Operations
| Operation | Pattern | ||
|---|---|---|---|
| Read | `Get-Content "file.json" -Raw | ConvertFrom-Json` | |
| Write | `$data | ConvertTo-Json -Depth 10 | Out-File "file.json" -Encoding UTF8` |
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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() |
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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.
When to Use
This skill is applicable to execute the workflow or actions described in the overview.
Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.
