问题
I am hashing all the files in one location, an origin folder, and writing the hashes to a variable and then doing the same to all the files in another location, a destination folder:
$origin = Get-ChildItem .\Test1 | Get-FileHash | Format-Table -Property Hash -HideTableHeaders
$destination = Get-ChildItem .\Test2 | Get-FileHash | Format-Table -Property Hash -HideTableHeaders
Then I am comparing them with Compare-Object like so:
Compare-Object $origin $destination
Now in my test I purposefully have deviations, so when the above code returned no differences I knew I had a problem.
Then I found out that if I do the following, that the hash values arn't there:
PS> Write-Host "$origin" Microsoft.PowerShell.Commands.Internal.Format.FormatStartData Microsoft.PowerShell.Commands.Internal.Format.GroupStartData Microsoft.PowerShell.Commands.Internal.Format.FormatEntryData Microsoft.PowerShell.Commands.Internal.Format.FormatEntryData Microsoft.PowerShell.Commands.Internal.Format.FormatEntryData Microsoft.PowerShell.Commands.Internal.Format.GroupEndData Microsoft.PowerShell.Commands.Internal.Format.FormatEndData
However, if I just type the following and press enter, then the hash values are present (like I want):
PS> $origin 6B86B273FF34FCE19D6B804EFF5A3F5747ADA4EAA22F1D49C01E52DDB7875B4B D4735E3A265E16EEE03F59718B9B5D03019C07D8B6C51F90DA3A666EEC13AB35 4E07408562BEDB8B60CE05C1DECFE3AD16B72230967DE01F640B7E4729B49FCE
I am assuming when I use Compare-Object
, that my variables are not presenting the hash values like I expected.
Does anyone know what is going on or have any recommendations? This is being used to ensure files are moved from an origin location to a destination location (this is one check in a script I'm working on). I am keeping this purely PowerShell, which means no xcopy
or robocopy
.
回答1:
Re use of Format-Table
to create the input collections for Compare-Object
:
Only ever use Format-*
cmdlets for display formatting; never use them if data must be programmatically processed.
Format-*
cmdlets output formatting instructions, not data - see this answer.
Therefore:
- Omit the
Format-Table
calls from your input-collection definition commands:
$origin=Get-ChildItem .\Test1 | Get-FileHash
$destination=Get-ChildItem .\Test2 | Get-FileHash
- Then pass the names of the properties to compare the objects by to
Compare-Object
:
Compare-Object $origin $destination -Property Path, Hash
Note the need to compare by both path and hash, to make sure that only files of the same name are compared.
As an aside: If you didn't specify -Property
, the objects would by default be compared by their .ToString()
value - and since the Microsoft.PowerShell.Commands.FileHashInfo
instances output by Get-FileHash
only ever stringify to that very type name (irrespective of their specific property values), no differences would be found.
As for $origin
vs. Write-Host $orgin
:
Just executing
$origin
is implicitly like executingWrite-Output $origin
- it writes to the success output stream (see about_Redirection), which by default goes to the console.- Success output that goes to the console is automatically formatted by PowerShell's rich output-formatting system.
Write-Host
, by contrast, serves a different purpose thanWrite-Output
:It writes directly to the console[1], bypassing PowerShell's success output stream and thereby also its usual formatting. Its primary purpose is to write status messages, interactive prompt messages, ... to the display - as opposed to outputting data.
Write-Host
itself applies output formatting, but only by simple.ToString()
stringification, which often yields unhelpful (type name-only) representations, as in your case.
See this answer for more information about the differences between Write-Output
and Write-Host
.
[1] Technically, since PowerShell version 5, Write-Host
output reaches the console via the information output stream (number 6
), but its primary purpose is still to write to the display as opposed to outputting data.
来源:https://stackoverflow.com/questions/58825933/xyz-and-write-host-xyz-giving-different-output