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powershell-windows

Skill130 starsChanged 10 months agoMITView on GitHub

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

We split this skill into the rules it gives an agent

5 rules. 4 are common, 0 are distinctive, and 1 is very specific to this project.

  • 4

    Common

    Most of the 9 edited versions we read keep these.

  • 0

    Distinctive

    This author's own choices. Worth a look.

  • 1

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Common:

    Rule: Use ASCII characters only in PowerShell scripts.

    line 38
  2. Common:

    Don't return inside try block

    line 81
  3. Common:

    Use finally for cleanup

    line 82
  4. Common:

    Rule: Use Join-Path for cross-platform safety.

    line 97
  5. Very specific:

    Rule: Always specify -Depth for nested objects.

    line 121

“Common” is measured: kept by at least 6 in 10 of the 9 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

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
$text.Lengthif ($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 pathC:\Users\User\file.txt
Variable pathJoin-Path $env:USERPROFILE "file.txt"
RelativeJoin-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)Out-Null`

8. JSON Operations

CRITICAL: Depth Parameter

❌ Wrong✅ Correct
ConvertTo-JsonConvertTo-Json -Depth 10

Rule: Always specify -Depth for nested objects.

File Operations

OperationPattern
Read`Get-Content "file.json" -RawConvertFrom-Json`
Write`$dataConvertTo-Json -Depth 10Out-File "file.json" -Encoding UTF8`

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

# 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.

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