PowerShell脚本报错：空值表达式调用及重复键问题求助

原始代码（第66行） #

$remotefilehash =  ($remoteFiles | Where-Object { -not ($_ | Select-String -Quiet -NotMatch -Pattern '^[a-f0-9]{32}(  )') } -replace '^[a-f0-9]{32}(  )', '$0=  ' -join "`n") | ConvertFrom-StringData

初始报错信息 #

Where-Object : A parameter cannot be found that matches parameter name 'replace'.
At P:\scripts\code\pcloud_sync.ps1:66 char:125
+ ... ing -Quiet -NotMatch -Pattern '^[a-f0-9]{32}(  )') } -replace '^[a-f0 ...
+                                                          ~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [Where-Object], ParameterBindingException
    + FullyQualifiedErrorId : NamedParameterNotFound,Microsoft.PowerShell.Commands.WhereObjectCommand

You cannot call a method on a null-valued expression.
At P:\scripts\code\pcloud_sync.ps1:74 char:1
+ $diffmd5 = $remotefilehash.GetEnumerator().Where({ -not $localHashSet ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

更新代码后的新报错 #

添加括号修正语法后，出现重复键报错：

ConvertFrom-StringData : Data item 'a3512c98c9e159c021ebbb76b238707e' in line 'a3512c98c9e159c021ebbb76b238707e  =  My
Pictures/Tony/Automatic Upload/Tony’s iPhone/2022-10-08 21-46-21 (2).mov' is already defined.
At P:\scripts\code\pcloud_sync.ps1:66 char:179
+ ... ace '^[a-f0-9]{32}(  )', '$0=  ' -join "`n") | ConvertFrom-StringData
+                                                    ~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [ConvertFrom-StringData], PSInvalidOperationException
    + FullyQualifiedErrorId : InvalidOperation,Microsoft.PowerShell.Commands.ConvertFromStringDataCommand

You cannot call a method on a null-valued expression.
At P:\scripts\code\pcloud_sync.ps1:74 char:1
+ $diffmd5 = $remotefilehash.GetEnumerator().Where({ -not $localHashSet ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

解决方案 #

1. 修复管道语法错误 #

初始报错是因为-replace被错误当作Where-Object的参数，需将Where-Object的过滤结果用括号包裹，确保-replace作用在过滤后的字符串集合上：

$remotefilehash =  (($remoteFiles | Where-Object { -not ($_ | Select-String -Quiet -NotMatch -Pattern '^[a-f0-9]{32}(  )') }) -replace '^[a-f0-9]{32}(  )', '$0=  ' -join "`n") | ConvertFrom-StringData

2. 处理$remoteFiles为空的情况 #

为避免空值导致后续操作报错，先确保$remoteFiles始终是数组类型，即使为空也不会返回$null：

$remoteFiles = @($remoteFiles) # 强制转为数组

或者在处理前添加空值判断：

if (-not $remoteFiles) {
    $remotefilehash = @{}
    # 可根据需求添加空值场景下的后续逻辑
} else {
    # 执行转换逻辑
}

3. 解决重复MD5键问题 #

ConvertFrom-StringData不允许重复键值对，需先按MD5值对过滤后的行去重。以下是保留每组最后一个重复项的处理方式：

# 过滤符合MD5格式的行
$filteredLines = $remoteFiles | Where-Object { -not ($_ | Select-String -Quiet -NotMatch -Pattern '^[a-f0-9]{32}(  )') }
# 按MD5值分组，保留每组最后一行
$uniqueLines = $filteredLines | Group-Object { $_ -replace '^([a-f0-9]{32})\s{2}.*', '$1' } | ForEach-Object { $_.Group[-1] }
# 转换为键值对哈希表
$remotefilehash = ($uniqueLines -replace '^[a-f0-9]{32}(  )', '$0=  ' -join "`n") | ConvertFrom-StringData

内容的提问来源于stack exchange，提问作者Tony