powershell-windows

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"

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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
}

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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.