PowerShell脚本删除指定日期前旧备份的语法错误排查求助

问题描述 #

需要编写PowerShell脚本删除指定日期（当前日期往前推60天）之前的旧备份文件，文件夹每周生成备份。原脚本尝试在foreach循环中同时提取文件的LastWriteTime和Name属性以筛选旧文件，但出现语法错误，无法正常执行。

原脚本代码 #

## Path
$path = "C:\SFTP_Root\SMGR"

## Get the current date
$Cur_dte = Get-Date
echo "Today is $Cur_dte"

## Old date (Subtract current date by 2 months i.e. 60 days)
$Old_dte = (Get-Date).AddDays(-60)
echo "Old date is $Old_dte"

## Loop to extract the date and name of the backup)
foreach (($i in Get-ChildItem -Path $path | select -ExpandProperty LastWriteTime) -and ($file in Get-ChildItem -Path $path | select -ExpandProperty Name))
    {
        if ($i -lt $Old_dte)
        {
        echo "$file is old; will be deleted"
        }
    elseif ($i -gt $Old_dte)
        {
        echo "$file is recent; won't be deleted"
        }
    }

报错信息 #

At C:\Temp\backups_clean.ps1:14 char:10
+ foreach (($i in Get-ChildItem -Path $path | select -ExpandProperty La ...
+          ~
Missing variable name after foreach.
At C:\Temp\backups_clean.ps1:14 char:14
+ foreach (($i in Get-ChildItem -Path $path | select -ExpandProperty La ...
+              ~~
Unexpected token 'in' in expression or statement.
At C:\Temp\backups_clean.ps1:14 char:13
+ foreach (($i in Get-ChildItem -Path $path | select -ExpandProperty La ...
+             ~
Missing closing ')' in expression.
At C:\Temp\backups_clean.ps1:14 char:81
+ ... ChildItem -Path $path | select -ExpandProperty LastWriteTime) -and ($ ...
+                                                                 ~
Unexpected token ')' in expression or statement.
At C:\Temp\backups_clean.ps1:14 char:95
+ ...  $path | select -ExpandProperty LastWriteTime) -and ($file in Get-Chi ...
+                                                                ~~
Unexpected token 'in' in expression or statement.
At C:\Temp\backups_clean.ps1:14 char:94
+ ... ath $path | select -ExpandProperty LastWriteTime) -and ($file in Get- ...
+                                                                  ~
Missing closing ')' in expression.
At C:\Temp\backups_clean.ps1:14 char:153
+ ... d ($file in Get-ChildItem -Path $path | select -ExpandProperty Name))
+                                                                        ~
Unexpected token ')' in expression or statement.
At C:\Temp\backups_clean.ps1:14 char:154
+ ... d ($file in Get-ChildItem -Path $path | select -ExpandProperty Name))
+                                                                         ~
Unexpected token ')' in expression or statement.
    + CategoryInfo          : ParserError: (:) [], ParseException
    + FullyQualifiedErrorId : MissingVariableNameAfterForeach

修复方案 #

错误原因 #

PowerShell的foreach语法不支持同时遍历两个独立集合，原脚本写法不符合语法规范。更关键的是，分开提取LastWriteTime和Name会导致两个列表无法保证对应关系（比如文件顺序变化时日期和文件名错位）。

修正后的脚本 #

直接遍历Get-ChildItem返回的文件对象，每个对象本身包含LastWriteTime、Name、FullName等所有属性，无需拆分提取：

## Path
$path = "C:\SFTP_Root\SMGR"

## Get the current date
$Cur_dte = Get-Date
Write-Host "Today is $Cur_dte"

## Old date (Subtract current date by 60 days)
$Old_dte = (Get-Date).AddDays(-60)
Write-Host "Old date is $Old_dte"

## Loop through each file in the target path
foreach ($file in Get-ChildItem -Path $path) {
    if ($file.LastWriteTime -lt $Old_dte) {
        Write-Host "$($file.Name) is old; will be deleted"
        # 实际执行删除时，移除下面的注释，-WhatIf用于预演删除操作，确认无误后再去掉
        # Remove-Item -Path $file.FullName -Force -WhatIf
    }
    else {
        Write-Host "$($file.Name) is recent; won't be deleted"
    }
}

关键改进点 #

1. 直接遍历文件对象，确保日期与文件名一一对应
2. 使用Write-Host替代echo（PowerShell中echo是Write-Output的别名，Write-Host更适合控制台输出信息）
3. 加入了带-WhatIf参数的删除命令，可先测试删除范围，避免误删
4. 简化了条件判断，无需单独处理-gt分支，用else覆盖即可

内容的提问来源于stack exchange，提问作者Melwyn John