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.