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