powershell-windows

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PowerShell Windows patterns. Critical pitfalls, operator syntax, error handling.

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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]
Infoℹ️ 🔵[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

ValueUse
StopDevelopment (fail fast)
ContinueProduction scripts
SilentlyContinueWhen 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

PatternUse
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

OperationSyntax
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

OperationPattern
Read`Get-Content "file.json" -Raw
Write`$data

9. Common Errors

Error MessageCauseFix
"parameter 'or'"Missing parenthesesWrap cmdlets in ()
"Unexpected token"Unicode characterUse ASCII only
"Cannot find property"Null objectCheck null first
"Cannot convert"Type mismatchUse .ToString()

10. Script Template

powershell
# 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.