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.

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.