Comparing two files

PowerShell Help
1

Hello All,

I am in the process of writing some code to compare two files.

  1. Place the data into variables
  2. Use get-content to obtain the content of the files
  3. Compare and echo the differences
$a = get-content "C:\temp\one.txt" $b = get-content "c:\temp\two.txt" Compare-Object $a $b -IncludeEqual

One.txt has a bunch of letters in it two.txt has nothing in it. This is my prototype as the end goal is to compare hotfixes in each file and then use compare-object to echo what is different.

 

However when I run the code I get the following error cant figure out what the issue is

Compare-Object : Cannot bind argument to parameter ‘DifferenceObject’ because it is null.
At line:1 char:19
+ Compare-Object $a $b
+ ~~
+ CategoryInfo : InvalidData: (:slight_smile: [Compare-Object], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationErrorNullNotAllowed,Microsoft.PowerShell.Commands.C
ompareObjectCommand

Regards

 

Fish and Chips

 

2

To compare file content you use hashing as in:

if ((Get-FileHash .\file1.txt).Hash -eq (Get-FileHash .\file2.txt).Hash) {
    'The 2 files are identical'
} else {
    'the 2 files are different'
}

This may be slow for large files across slow wan links.
A less accurate but faster method is to compare file sizes in bytes, and their LastWriteTime

3

The error is clear, $b is null or nothing as you specified you are providing nothing in the file. Basically, the error is you need to provide a value to compare against. How are you populating the hotfixes into the files? Have you looked at Get-Hotfix?

PS C:\Users\rasim> $list1 = Get-Hotfix

PS C:\Users\rasim> $list1

Source        Description      HotFixID      InstalledBy          InstalledOn              
------        -----------      --------      -----------          -----------              
DESKTOP-MG... Update           KB4537572     NT AUTHORITY\SYSTEM  3/4/2020 12:00:00 AM     
DESKTOP-MG... Security Update  KB4516115     NT AUTHORITY\SYSTEM  11/12/2019 12:00:00 AM   
DESKTOP-MG... Update           KB4517245     NT AUTHORITY\SYSTEM  12/26/2019 12:00:00 AM   
DESKTOP-MG... Security Update  KB4521863     NT AUTHORITY\SYSTEM  11/12/2019 12:00:00 AM   
DESKTOP-MG... Security Update  KB4524244     NT AUTHORITY\SYSTEM  2/13/2020 12:00:00 AM    
DESKTOP-MG... Security Update  KB4524569     NT AUTHORITY\SYSTEM  11/14/2019 12:00:00 AM   
DESKTOP-MG... Security Update  KB4525419     NT AUTHORITY\SYSTEM  11/12/2019 12:00:00 AM   
DESKTOP-MG... Security Update  KB4528759     NT AUTHORITY\SYSTEM  1/14/2020 12:00:00 AM    
DESKTOP-MG... Security Update  KB4537759     NT AUTHORITY\SYSTEM  2/13/2020 12:00:00 AM    
DESKTOP-MG... Security Update  KB4538674     NT AUTHORITY\SYSTEM  2/13/2020 12:00:00 AM    
DESKTOP-MG... Security Update  KB4541338     NT AUTHORITY\SYSTEM  3/10/2020 12:00:00 AM    
DESKTOP-MG... Update           KB4551762     NT AUTHORITY\SYSTEM  3/13/2020 12:00:00 AM
-

Then you can do:

$list1 = Get-Hotfix -ComputerName Computer123
$list2 = Get-Hotfix -ComputerName Computer321

Compare-Object -ReferenceObject $list1 -DifferenceObject $list2 -Property HotFixId

Get-Content is returning an array of strings. If you want to use the list you can do this:

#Emulate Get-Content
$list1 = @"
hotfix1
hotfix2
hotfix3
hotfix4
"@ -split [environment]::NewLine

#Emulate Get-Content
$list2 = @"
hotfix1
hotfix4
"@ -split [environment]::NewLine

Compare-Object -ReferenceObject $list1 -DifferenceObject $list2

A little more structured would be:

$list1 = @"
hotfix1
hotfix2
hotfix3
hotfix4
"@ | ConvertFrom-CSV -Header HotfixId

$list2 = @"
hotfix1
hotfix4
"@ | ConvertFrom-CSV -Header HotfixId

Compare-Object -ReferenceObject $list1 -DifferenceObject $list2 -Property HotfixId
4

Hi Sam\Rob

Thanks for your input. I know of this get-hotfix command and have experimented with it. However I am writing small prototype programs to see if they work first before moving onto building get-hotfix into my script.

The end goal i envisage is for me to run the get-hotfix on two servers then generate a file with a list of hotfixes in there. Then compared the two files to see where the difference is in the hotfixes.

 

Hope this makes sense

 

Thanks

 

Fish and Chips

 

 

 

5

Have you considered capturing the results of the Get-HotFix execution as files via export-csv or export-clixml? Then when you want to compare, recreate the objects by importing the files (import-csv or import-clixml) and then compare the objects.

Get-HotFix | Export-CSV -Path C:\Temp\MyHotFixes.csv
Get-HotFix -ComputerName | Export-CSV -Path c:\temp\YourHotFixes.csv

# ...Fifteen Minutes Later...

$X = IMport-Csv -Path C:\Temp\MyHostFixes.csv
$Y = Import-CSV -Path C:\Temp\YourHotFixes.csv

Compare-Object $X $Y -Property HotFixID