PowerShell函数输出异常：如何仅获取工作日天数而非额外日期？

我编写了PowerShell函数Get-WorkingDay，接收起始日期（startDate）和需添加的天数（Duration）参数，用于计算其中的工作日数量。计算逻辑整体正常，但输出存在问题：我需要仅返回工作日数量，却同时得到了最后检查的日期和工作日数。

当起始日期为2014.01.21时，输出结果为2014.01.31 00:00:00 7，但我只需要数字7。

函数代码如下：

Function Get-WorkingDay{
    param(
        [Parameter(Mandatory=$True,Position=1)]
        [datetime]$startDate,
        [Parameter(Mandatory=$True,Position=2)]
        [int]$Duration    
        )

        Write-Host $startDate
        Write-Host $Duration


    $holidays = @(
        (Get-Date -Date '2014-01-01'),            # New_Years_Day2014
        (Get-Date -Date '2014-01-20'),            # Martin_Luther_King2014
        (Get-Date -Date '2014-02-17'),            # Washingtons_Birthday2014
        (Get-Date -Date '2014-04-18'),            # Good_Friday2014 
        (Get-Date -Date '2014-05-26'),            # Memorial_Day2014 
        (Get-Date -Date '2014-07-04'),            # Independence_Day2014
        (Get-Date -Date '2014-09-01'),            # Labor_Day2014
        (Get-Date -Date '2014-11-27'),            # Thanksgiving_Day2014
        (Get-Date -Date '2014-12-25'),            # Christmas2014
        (Get-Date -Date '2015-01-01'),            # New_Years_Day2015
        (Get-Date -Date '2015-01-19'),            # Martin_Luther_King2015
        (Get-Date -Date '2015-02-16'),            # Washingtons_Birthday2015 
        (Get-Date -Date '2015-04-03'),            # Good_Friday2015 
        (Get-Date -Date '2015-05-25'),            # Memorial_Day2015 
        (Get-Date -Date '2015-07-03'),            # Independence_Day2015
        (Get-Date -Date '2015-09-07'),            # Labor_Day2015 
        (Get-Date -Date '2015-11-26'),            # Thanksgiving_Day2015
        (Get-Date -Date '2015-12-25')             # Christmas2015
        )

        $dateIndex = $startDate.AddDays(1)
        [Int]$WorkingDays = 0
        Write-Host "working days before counting" $WorkingDays
        

        For($DayIndex = 1; $DayIndex -le $Duration; $DayIndex++){
            
            Write-Host "getting into for loop"
            Write-Host "day nr" $DayIndex
            Write-Host "date" $dateIndex
            Write-Host "duration" $Duration
        
           Do{
                If (("Sunday","Saturday" -contains $dateIndex.DayOfWeek) -or ($holidays -contains $dateIndex)){
                    # This is not a working day. Check the next day.
                    Write-Host "$($dateIndex.Date) is a $($dateIndex.DayOfWeek) and is weekend or holiday and it's a day no $DayIndex, working day no $WorkingDays"
                    
                    If (("Saturday" -contains $dateIndex.DayOfWeek) -or ($holidays -contains $dateIndex.AddDays(1))){
                        $DayIndex += 1
                        }
                    
                    $dateIndex = $dateIndex.AddDays(1)
                    $isWorkingDay = $False
                } Else {
                    # Current $dateIndex is a working day.
                    
                    If (!$isWorkingDay) {
                        $DayIndex += 1
                        }

                    $WorkingDays += 1
                    $isWorkingDay = $True
                    Write-Host "$($dateIndex.Date) is a $($dateIndex.DayOfWeek) and is a working day and it's a day no $DayIndex, working day no $WorkingDays"
                    Write-Host "Working days" $WorkingDays
                }
            } 
            
            While(!$isWorkingDay)
            # Set the $dateIndex to the next day.
            $dateIndex = $dateIndex.AddDays(1)    
        }

        # The last date was the end one. Minus the day. 
        $dateIndex.AddDays(-1)

        Write-Host "Final working days $WorkingDays"
        Write-Output $WorkingDays
}

问题原因 #

• PowerShell默认行为：未被赋值给变量、未被抑制输出的表达式，其结果会自动流入输出管道。
• 函数中$dateIndex.AddDays(-1)这一行没有做任何处理，它的计算结果（一个datetime对象）会被输出到管道。
• 后续的Write-Output $WorkingDays又输出了工作日数字，所以最终管道里有两个输出内容：日期对象和数字7，导致结果同时显示两者。

解决方法 #

你可以任选以下一种方式修正：

方式1：移除无用的日期计算行 #

如果这行代码只是调试遗留的，没有实际用途，直接删除$dateIndex.AddDays(-1)即可。

方式2：抑制该表达式的输出 #

如果需要保留这行代码（比如后续扩展功能时可能用到），可以通过以下方式阻止它输出到管道：

• 使用[void]前缀：

  [void]$dateIndex.AddDays(-1)
  

• 将结果管道到Out-Null：

  $dateIndex.AddDays(-1) | Out-Null
  

• 将结果赋值给一个临时变量（即使不用这个变量）：

  $tempDate = $dateIndex.AddDays(-1)
  

额外建议 #

函数中大量的Write-Host是调试输出，正式使用时建议移除，避免干扰最终的纯净输出。

内容的提问来源于stack exchange，提问作者Fiilli