Powershell Windows

Intermediatev1.0.0

> Critical patterns and pitfalls for Windows PowerShell. | ❌ Wrong | ✅ Correct | |----------|-----------|.

Content

> 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:

code

$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

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.

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

FAQ

Discussion

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❌ 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))`

Purpose

❌ Don't Use

✅ Use

Success

✅ ✓

[OK] [+]

Error

❌ ✗ 🔴

[!] [X]

Warning

⚠️ 🟡

[*] [WARN]

Info

ℹ️ 🔵

[i] [INFO]

Progress

⏳

[...]

❌ Wrong

✅ Correct

`$array.Count -gt 0`

`$array -and $array.Count -gt 0`

`$text.Length`

`if ($text) { $text.Length }`

❌ Wrong

✅ Correct

`"Value: $($obj.prop.sub)"`

Store in variable first

Value

Use

Stop

Development (fail fast)

Continue

Production scripts

SilentlyContinue

When errors expected

Pattern

Use

Literal path

`C:\Users\User\file.txt`

Variable path

`Join-Path $env:USERPROFILE "file.txt"`

Relative

`Join-Path $ScriptDir "data"`

Operation	Syntax
Empty array	`$array = @()`
Add item	`$array += $item`
ArrayList add	`$list.Add($item)	Out-Null`

Operation

Syntax

Empty array

`$array = @()`

Add item

`$array += $item`

ArrayList add

`$list.Add($item)

Out-Null`

❌ Wrong

✅ Correct

`ConvertTo-Json`

`ConvertTo-Json -Depth 10`

Operation	Pattern
Read	`Get-Content "file.json" -Raw	ConvertFrom-Json`
Write	`$data	ConvertTo-Json -Depth 10	Out-File "file.json" -Encoding UTF8`

Operation

Pattern

Read

`Get-Content "file.json" -Raw

ConvertFrom-Json`

Write

`$data

ConvertTo-Json -Depth 10

Out-File "file.json" -Encoding UTF8`

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

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.