改写PowerShell脚本避免无匹配文件时等待用户输入

问题场景 #

运行以下代码片段时：

Get-Childitem -Filter '*.bak' -Recurse -exclude *baseline*  |  Where-Object {$_.LastWriteTime -lt (Get-Date).AddDays(-30)} |  foreach-object 
{

当没有符合条件的文件时，脚本会弹出提示并挂起等待输入：

cmdlet ForEach-Object at command pipeline position 3
Supply values for the following parameters:
Process[0]:

用户尝试的代码 #

write-host ""
write-host $DBA_BackupFileShare_NME
cd $DBA_BackupFileShare_NME\SQLServerBackup
# @( Get-Childitem -Filter '*.bak' -Recurse -exclude *baseline* ) |  
#   Where-Object {$_.LastWriteTime -lt (Get-Date).AddDays(-30)} |  
#   ForEach-Object 
#   {
#     write-host ("{0}" -f $_.FullName)
##     [System.IO.File]::Delete($_.FullName)
#   }

[System.IO.Directory]::EnumerateFiles('.', '*.bak',[System.IO.SearchOption]::AllDirectories <# Means Recursive#>) |         Where-Object {[System.IO.Path]::GetFileName($_) -notcontains 'baseline'} 
ForEach-Object { Get-Item -Path $_ } |
Where-Object {$_.LastWriteTime -lt (Get-Date).AddDays(-30)} |  
ForEach-Object 
{
 write-host ("{0}" -f $_.FullName)
 #      [System.IO.File]::Delete($_.FullName)
}

问题原因与解决方案 #

核心原因 #

当管道无输出对象时，ForEach-Object如果和脚本块{分两行写，PowerShell会误认为你未提供必填的Process参数，从而触发交互式输入请求，导致脚本挂起。

可行解决方案 #

方案1：修正脚本块语法

把ForEach-Object和脚本块的{放在同一行，消除语法歧义：

Get-ChildItem -Filter '*.bak' -Recurse -Exclude *baseline* | 
    Where-Object {$_.LastWriteTime -lt (Get-Date).AddDays(-30)} | 
    ForEach-Object {
        Write-Host ("{0}" -f $_.FullName)
        # [System.IO.File]::Delete($_.FullName)
    }

方案2：强制包装为数组

用@()将Get-ChildItem的结果包装成数组，即使无匹配文件也会生成空数组，而非空管道：

@(Get-ChildItem -Filter '*.bak' -Recurse -Exclude *baseline*) | 
    Where-Object {$_.LastWriteTime -lt (Get-Date).AddDays(-30)} | 
    ForEach-Object {
        Write-Host ("{0}" -f $_.FullName)
        # [System.IO.File]::Delete($_.FullName)
    }

方案3：修正你尝试的代码

你的EnumerateFiles思路可行，但有两处错误需要调整：

1. -notcontains是数组操作符，判断单个文件名是否包含字符串要用-notlike
2. Where-Object和后续ForEach-Object之间缺少管道符|

修正后的代码：

Write-Host ""
Write-Host $DBA_BackupFileShare_NME
Set-Location $DBA_BackupFileShare_NME\SQLServerBackup

[System.IO.Directory]::EnumerateFiles('.', '*.bak', [System.IO.SearchOption]::AllDirectories) | 
    Where-Object {[System.IO.Path]::GetFileName($_) -notlike '*baseline*'} |
    ForEach-Object { Get-Item -Path $_ } |
    Where-Object {$_.LastWriteTime -lt (Get-Date).AddDays(-30)} |  
    ForEach-Object {
        Write-Host ("{0}" -f $_.FullName)
        # [System.IO.File]::Delete($_.FullName)
    }

内容的提问来源于stack exchange，提问作者pithhelmet