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.
