Powershell速度:如何加快ForEach-Object MD5/哈希检查 [英] Powershell Speed: How to speed up ForEach-Object MD5/hash check

问题描述

我正在对5亿个文件运行以下MD5检查，以检查重复项.这些脚本要花很长时间才能运行，我想知道如何加快运行速度.我怎样才能加快速度?当哈希已经存在时，我可以使用try catch循环而不是contains来引发错误吗?你们都会推荐什么?

I'm running the following MD5 check on 500 million files to check for duplicates. The scripts taking forever to run and I was wondering how to speed it up. How could I speed it up? Could I use a try catch loop instead of contains to throw an error when the hash already exists instead? What would you all recommend?

$folder = Read-Host -Prompt 'Enter a folder path'

$hash = @{}
$lineCheck = 0

Get-ChildItem $folder -Recurse | where {! $_.PSIsContainer} | ForEach-Object {
    $lineCheck++
    Write-Host $lineCheck
    $tempMD5 = (Get-FileHash -LiteralPath $_.FullName -Algorithm MD5).Hash;

    if(! $hash.Contains($tempMD5)){
        $hash.Add($tempMD5,$_.FullName)
    }
    else{
        Remove-Item -literalPath $_.fullname;
    }
} 

推荐答案

如注释中所建议，如果与首先找到的文件长度匹配，则可以考虑仅散列文件 .这意味着您将不会为任何唯一的文件长度调用昂贵的哈希方法.

As suggested in the comments, you might consider to start hashing files only if there is a match with the file length found first. Meaning that you will not invoke the expensive hash method for any file length that is unique.

_{*注意: Write-Host 命令本身非常昂贵，因此，我将不显示每次迭代( Write-Host $lineCheck )，但例如仅当找到匹配项时.}

_{*Note: that the Write-Host command is quite expensive by itself, therefore I would not display every iteration (Write-Host $lineCheck) but e.g. only when a match is found.}

$Folder = Read-Host -Prompt 'Enter a folder path'

$FilesBySize = @{}
$FilesByHash = @{}

Function MatchHash([String]$FullName) {
    $Hash = (Get-FileHash -LiteralPath $FullName -Algorithm MD5).Hash
    $Found = $FilesByHash.Contains($Hash)
    If ($Found) {$Null = $FilesByHash[$Hash].Add($FullName)}
    Else {$FilesByHash[$Hash] = [System.Collections.ArrayList]@($FullName)}
    $Found
}

Get-ChildItem $Folder -Recurse | Where-Object -Not PSIsContainer | ForEach-Object {
    $Files = $FilesBySize[$_.Length]
    If ($Files) {
        If ($Files.Count -eq 1) {$Null = MatchHash $Files[0]}
        If ($Files.Count -ge 1) {If (MatchHash $_) {Write-Host 'Found match:' $_.FullName}}
        $Null = $FilesBySize[$_.Length].Add($_.FullName)
    } Else {
        $FilesBySize[$_.Length] = [System.Collections.ArrayList]@($_.FullName)
    }
}

显示找到的重复项:

ForEach($Hash in $FilesByHash.GetEnumerator()) {
    If ($Hash.Value.Count -gt 1) {
        Write-Host 'Hash:' $Hash.Name
        ForEach ($File in $Hash.Value) {
            Write-Host 'File:' $File
        }
    }
}

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