Code Review Asked on November 28, 2021
I’m moving some files from a Linux machine to a Windows machine over a low-speed, possibly buggy experimental communications channel that I want to test. One of the tests is to transfer large numbers of large and small files and verify their cryptographic hashes at the receiving end. On the Linux side, we’re using md5sum
to generate file hashes like so:
md5sum * > files.md5
Then the files are transmitted from the Linux machine to the Windows 10 machine. What I’d like to do next is to verify the hashes on the plain-vanilla Windows machine (no Cygwin installed). So to mimic the default operation of md5sum -c files.md5
which would go through, line by line and verify each md5 checksum, I’ve written this Powershell script. I’m a lot more at home in bash than in Powershell, so thought I might benefit from a review.
param (
[Parameter(Mandatory=$true)][string]$infile
)
$basedir = Split-Path -Parent $infile
$badcount = 0
foreach ($line in [System.IO.File]::ReadLines("$infile")) {
$sum, $file = $line.split(' ')
$fullfile = "$basedir$file"
$filehash = Get-FileHash -Algorithm MD5 $fullfile
if ($sum -eq $filehash.Hash) {
Write-Host $file ": OK"
} else {
Write-Host $file ": FAILED"
$badcount++
}
}
if ($badcount -gt "0") {
Write-Host "WARNING:" $badcount "computed checksums did NOT match"
}
here are a few changes i would make. [grin] the ideas ...
Get-Content
instead of ReadLines()
[PSCustomObject]
to hold the resulting items that you wantwhat it does ...
#region/#endregion
block when you are ready to use your own data.'__N/A__'
$Result
collection@()
and add .Count
to the end.the code ...
$SourceDir = $env:TEMP
$HashFileName = 'FileHashList.txt'
$FullHashFileName = Join-Path -Path $SourceDir -ChildPath $HashFileName
#region >>> make a hash list to compare with
# remove this entire "#region/#endregion" block when ready to work with your real data
$HashList = Get-ChildItem -LiteralPath $SourceDir -Filter '*.log' -File |
ForEach-Object {
'{0} {1}' -f $_.Name, (Get-FileHash -LiteralPath $_.FullName-Algorithm 'MD5').Hash
}
# munge the 1st two hash values
$HashList[0] = $HashList[0] -replace '.{5}$', '--BAD'
$HashList[1] = $HashList[1] -replace '.{5}$', '--BAD'
$HashList |
Set-Content -LiteralPath $FullHashFileName
#endregion >>> make a hash list to compare with
$Result = foreach ($Line in (Get-Content -LiteralPath $FullHashFileName))
{
$TestFileName, $Hash = $Line.Split(' ')
$FullTestFileName = Join-Path -Path $SourceDir -ChildPath $TestFileName
if (Test-Path -LiteralPath $FullTestFileName)
{
$THash = (Get-FileHash -LiteralPath $FullTestFileName -Algorithm 'MD5').Hash
}
else
{
$THash = '__N/A__'
}
[PSCustomObject]@{
FileName = $TestFileName
CopyOK = $THash -eq $Hash
OriHash = $Hash
CopyHash = $THash
}
}
$Result.Where({$_.CopyOK -eq $False})
output [with the 1st two hash values deliberately munged] ...
FileName CopyOK OriHash CopyHash
-------- ------ ------- --------
Genre-List_2020-07-07.log False 7C0C605EA7561B7020CBDAE24D1--BAD 7C0C605EA7561B7020CBDAE24D140E40
Genre-List_2020-07-14.log False 20F234ACE66B860821CF8F8BD5E--BAD 20F234ACE66B860821CF8F8BD5EC144D
Answered by Lee_Dailey on November 28, 2021
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