powershell@foreach@foreach-object@continue的行为

文章目录

• powershell@foreach@foreach-object@continue的行为
• • ref
  • foreach@foreach-object
  • • What is a cmdlet?
  • break@continue
  • 案例
  • • foreach@continue
    • • loop-foreach
      • cmdlet-foreach
      • 运行结果
    • 其他方案

powershell@foreach@foreach-object@continue的行为

ref

• about Continue - PowerShell | Microsoft Learn
• powershell - Why does ‘continue’ behave like ‘break’ in a Foreach-Object? - Stack Overflow

foreach@foreach-object

• about Foreach - PowerShell | Microsoft Learn

  • powershell/module/microsoft.powershell.core/about/about_foreach
  • 这是一个powershell 遍历可迭代对象的基本语法,属于循环(loop)中的一种
  • 不妨称它为loop-foreach

• ForEach-Object (Microsoft.PowerShell.Core) - PowerShell | Microsoft Learn

  • powershell/module/microsoft.powershell.core/foreach-object
  • 这是一个powershell cmdlet(powershell命令),不是一种循环,可能是基于基本语法编制而成的功能性命令
  • 不妨称它为cmdlet-foreach

• 这一点区别将会在使用continue的时候显现出来

  • continue放在在某个Loop中时(比如foreach),那么它的行为就像c语言那样
  • 如果是放在foreach-object(有时候简写为foreach,区分loop-foreach),充当scriptblock
  • 这时候,会尝试跳过最近的loop语法层(如果存在的话)

• What is a PowerShell command? - PowerShell | Microsoft Learn

What is a cmdlet?

• Cmdlets are native PowerShell commands, not stand-alone executables.
• Cmdlets are collected into PowerShell modules that can be loaded on demand.
• Cmdlets can be written in any compiled .NET language or in the PowerShell scripting language itself.

break@continue

• about Break - PowerShell | Microsoft Learn
• about Continue - PowerShell | Microsoft Learn

案例

foreach@continue

loop-foreach

• Write-Output 'foreach-loop'
  $l = 1..5
  foreach ($elem in $l)
  {
      if ($elem -eq 3)
      {
          continue;
          # not return here
      }
      Write-Output $elem
  }
  

cmdlet-foreach

• Write-Output 'foreach-object(cmdlet)'
  1..5 | ForEach-Object {
      if ($_ -eq 3 )
      {
          return 
          #not continue here
      }
      Write-Output $_
  
  }
  

运行结果

• foreach-loop
  1
  2
  4
  5
  foreach-object(cmdlet)
  1
  2
  4
  5
  

其他方案

• 加一层if-else可以在cmdlet中模拟continue的字面行为
  • 但是这增加了不必要的代码
  • 而且不够优雅
• 做过滤的时候where-object有时候比foreach-object更加合适