PowerShellPowerShell避坑指南

Output Behavior

• - Everything not captured goes to output — even without return or INLINECODE1
• INLINECODE2 doesn't stop output — previous uncaptured expressions still output
• INLINECODE3 bypasses pipeline — use for display only, not data
• Assign to $null to suppress — INLINECODE5
• INLINECODE6 cast also suppresses — INLINECODE7

Array Gotchas

• - Single item result is scalar, not array — @(Get-Item .) forces array
• Empty result is $null, not empty array — check with if ($result) carefully
• Array unrolling in pipeline — @(1,2,3) | ForEach sends items one by one
• INLINECODE12 on array creates new array — slow in loops, use INLINECODE13
• INLINECODE14 is array operator — ,$item wraps single item in array

Comparison Operators

• - -eq, -ne, -gt, -lt — not ==, !=, >, INLINECODE23
• INLINECODE24 with wildcards, -match with regex — both return bool
• INLINECODE26 for array membership — $arr -contains $item, not $item -in $arr (though -in works too)
• Case-insensitive by default — -ceq, -cmatch for case-sensitive
• INLINECODE32 on left side — $null -eq $var prevents array comparison issues

String Handling

• - Double quotes interpolate — "Hello $name" expands variable
• Single quotes literal — '$name' stays as literal text
• Subexpression for complex — "Count: $($arr.Count)" for properties/methods
• Here-strings for multiline — @" ... "@ or INLINECODE38
• Backtick escapes — ` n ` for newline, t ` for tab ## Pipeline - $ or $PSItem is current object — same thing, $ more common - ForEach-Object for pipeline — foreach statement doesn't take pipeline - -PipelineVariable saves intermediate — Get-Service -PV svc | Where ... - Pipeline processes one at a time — unless function doesn't support streaming ## Error Handling - $ErrorActionPreference sets default — Stop, Continue, SilentlyContinue - -ErrorAction Stop per command — makes non-terminating errors terminating - try/catch only catches terminating — set ErrorAction Stop first - $? is last command success — $LASTEXITCODE for native commands ## Common Mistakes - No space before { in if — if($x){ works but if ($x) { preferred - = is assignment in conditions — use -eq for comparison - Function return array unrolls — return ,@($arr) to keep array - Get-Content returns lines array — -Raw for single string - Select-Object creates new object — properties are copies, not references ## Cross-Platform - pwsh is PowerShell 7+ — powershell is Windows PowerShell 5.1 - Paths use / or \ — Join-Path for portable - Environment vars: $env:VAR — works on all platforms - Aliases differ across platforms — ls, cat` may not exist, use full cmdlet names